Patent Publication Number: US-9413803-B2

Title: User input back channel for wireless displays

Description:
This application claims the benefit of 
     U.S. Provisional Application No. 61/435,194, filed 21 Jan. 2011; 
     U.S. Provisional Application No. 61/447,592, filed 28 Feb. 2011; 
     U.S. Provisional Application No. 61/448,312, filed 2 Mar. 2011; 
     U.S. Provisional Application No. 61/450,101, filed 7 Mar. 2011; 
     U.S. Provisional Application No. 61/467,535, filed 25 Mar. 2011; 
     U.S. Provisional Application No. 61/467,543, filed 25 Mar. 2011; 
     U.S. Provisional Application No. 61/514,863, filed 3 Aug. 2011; and 
     U.S. Provisional Application No. 61/544,475, filed 7 Oct. 2011; 
     the entire contents each of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to techniques for transmitting data between a wireless source device and a wireless sink device. 
     BACKGROUND 
     Wireless display (WD) or Wi-Fi Display (WFD) systems include a wireless source device and one or more wireless sink devices. The source device and each of the sink devices may be either mobile devices or wired devices with wireless communication capabilities. One or more of the source device and the sink devices may, for example, include mobile telephones, portable computers with wireless communication cards, personal digital assistants (PDAs), portable media players, or other such devices with wireless communication capabilities, including so-called “smart” phones and “smart” pads or tablets, e-readers, or any type of wireless display, video gaming devices, or other types of wireless communication devices. One or more of the source device and the sink devices may also include wired devices such as televisions, desktop computers, monitors, projectors, and the like, that include communication capabilities. 
     The source device sends media data, such as audio video (AV) data, to one or more of the sink devices participating in a particular media share session. The media data may be played back at both a local display of the source device and at each of the displays of the sink devices. More specifically, each of the participating sink devices renders the received media data on its screen and audio equipment. 
     SUMMARY 
     This disclosure generally describes a system where a wireless sink device can communicate with a wireless sink device. As part of a communication session, a wireless source device can transmit audio and video data to the wireless sink device, and the wireless sink device can transmit user inputs received at the wireless sink device back to the wireless source device. In this manner, a user of the wireless sink device can control the wireless source device and control the content that is being transmitted from the wireless source device to the wireless sink device. 
     In one example, a method of transmitting user input data from a wireless sink device to a wireless source includes obtaining user input data at the wireless sink device; generating payload data describing the user input data; generating a data packet comprising a data packet header and the payload data; and, transmitting the data packet to the wireless source device. 
     In another example, a wireless sink device is configured to transmit user input data to a wireless source device. The wireless sink device includes a memory storing instructions; one or more processors configured to execute the instructions, wherein upon execution of the instructions the one or more processors cause obtaining user input data at the wireless sink device, generating payload data describing the user input data, and generating a data packet comprising a data packet header and the payload data. The wireless sink device also includes a transport unit to transmit the data packet to the wireless source device. 
     In another example, a computer-readable storage medium stores instructions that upon execution by one or more processors cause the one or more processors to perform a method of transmitting user input data from a wireless sink device to a wireless source device. The method includes obtaining user input data at the wireless sink device; generating payload data describing the user input data; generating a data packet comprising a data packet header and the payload data; and, transmitting the data packet to the wireless source device. 
     In another example, a wireless sink device is configured to transmit user input data to a wireless source device. The wireless sink device includes means for obtaining user input data at the wireless sink device; means for generating payload data describing the user input data; means for generating a data packet comprising a data packet header and the payload data; and, means for transmitting the data packet to the wireless source device. 
     In another example, a method of receiving input data from a wireless sink device at a wireless source device includes receiving from the wireless sink device a data packet, wherein the data packet comprises a data packet header and payload data, wherein the payload data comprises data describing details of a user input; parsing the data packet to determine an input type value in an input type field in the payload data; and, processing the data describing details of the user input based on the input type value. 
     In another example, a wireless source device is configured to receive user input data from a wireless sink device. The wireless source device includes a transport unit to receive from the wireless sink device a data packet, wherein the data packet comprises a data packet header and payload data, wherein the payload data comprises data describing details of a user input; a memory storing instructions; one or more processors configured to execute the instructions, wherein upon execution of the instructions the one or more processors cause parsing the data packet to determine an input type value in an input type field in the payload data and processing the data describing details of the user input based on the input type value. 
     In another example, a computer-readable storage medium stores instructions that upon execution by one or more processors cause the one or more processors to perform a method of receiving user input data from a wireless sink device at a wireless source device. The method includes receiving from the wireless sink device a data packet, wherein the data packet comprises a data packet header and payload data, wherein the payload data comprises data describing details of a user input; parsing the data packet to determine an input type value in an input type field in the payload data; and, processing the data describing details of the user input based on the input type value. 
     In another example, a wireless source device is configured to receive user input data from a wireless sink device. The wireless source device includes means for receiving from the wireless sink device a data packet, wherein the data packet comprises a data packet header and payload data, wherein the payload data comprises data describing details of a user input; means for parsing the data packet to determine an input type value in an input type field in the payload data; and means for processing the data describing details of the user input based on the input type value. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a block diagram illustrating an example of a source/sink system that may implement techniques of this disclosure. 
         FIG. 1B  is a block diagram illustrating an example of a source/sink system with two sink devices. 
         FIG. 2  shows an example of a source device that may implement techniques of this disclosure. 
         FIG. 3  shows an example of a sink device that may implement techniques of this disclosure. 
         FIG. 4  shows a block diagram of a transmitter system and a receiver system that may implement techniques of this disclosure. 
         FIGS. 5A and 5B  show example message transfer sequences for performing capability negotiations according to techniques of this disclosure. 
         FIG. 6  shows an example data packet that may be used for delivering user input data obtained at a sink device to a source device. 
         FIGS. 7A and 7B  are flow charts illustrating techniques of this disclosure that may be used for capability negotiation between a source device and a sink device. 
         FIGS. 8A and 8B  are flow charts illustrating techniques of this disclosure that may be used for transmitting and receiving data packets with user input data. 
         FIGS. 9A and 9B  are flow charts illustrating techniques of this disclosure that may be used for transmitting and receiving data packets with user input data. 
         FIGS. 10A and 10B  are flow charts illustrating techniques of this disclosure that may be used for transmitting and receiving data packets with timestamp information and user input data. 
         FIGS. 11A and 11B  are flow charts illustrating techniques of this disclosure that may be used for transmitting and receiving data packets with timestamp information and user input data. 
         FIGS. 12A and 12B  are flow charts illustrating techniques of this disclosure that may be used for transmitting and receiving data packets that include voice commands. 
         FIGS. 13A and 13B  are flow charts illustrating techniques of this disclosure that may be used for transmitting and receiving data packets with multi-touch user input commands. 
         FIGS. 14A and 14B  are flow charts illustrating techniques of this disclosure that may be used for transmitting and receiving data packets with user input data forwarded form a third party device. 
         FIGS. 15A and 15B  are flow charts illustrating techniques of this disclosure that may be used for transmitting and receiving data packets. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure generally describes a system where a wireless sink device can communicate with a wireless sink device. As part of a communication session, a wireless source device can transmit audio and video data to the wireless sink device, and the wireless sink device can transmit user inputs received at the wireless sink device back to the wireless source device. In this manner, a user of the wireless sink device can control the wireless source device and control the content that is being transmitted from the wireless source device to the wireless sink device. 
       FIG. 1A  is a block diagram illustrating an exemplary source/sink system  100  that may implement one or more of the techniques of this disclosure. As shown in  FIG. 1A , system  100  includes source device  120  that communicates with sink device  160  via communication channel  150 . Source device  120  may include a memory that stores audio/video (A/V) data  121 , display  122 , speaker  123 , audio/video encoder  124  (also referred to as encoder  124 ), audio/video control module  125 , and transmitter/receiver (TX/RX) unit  126 . Sink device  160  may include display  162 , speaker  163 , audio/video decoder  164  (also referred to as decoder  164 ), transmitter/receiver unit  166 , user input (UI) device  167 , and user input processing module (UIPM)  168 . The illustrated components constitute merely one example configuration for source/sink system  100 . Other configurations may include fewer components than those illustrated or may include additional components than those illustrated. 
     In the example of  FIG. 1A , source device  120  can display the video portion of audio/video data  121  on display  122  and can output the audio portion of audio/video data  121  on speaker  123 . Audio/video data  121  may be stored locally on source device  120 , accessed from an external storage medium such as a file server, hard drive, external memory, Blu-ray disc, DVD, or other physical storage medium, or may be streamed to source device  120  via a network connection such as the internet. In some instances audio/video data  121  may be captured in real-time via a camera and microphone of source device  120 . Audio/video data  121  may include multimedia content such as movies, television shows, or music, but may also include real-time content generated by source device  120 . Such real-time content may for example be produced by applications running on source device  120 , or video data captured, e.g., as part of a video telephony session. As will be described in more detail, such real-time content may in some instances include a video frame of user input options available for a user to select. In some instances, audio/video data  121  may include video frames that are a combination of different types of content, such as a video frame of a movie or TV program that has user input options overlaid on the frame of video. 
     In addition to rendering audio/video data  121  locally via display  122  and speaker  123 , audio/video encoder  124  of source device  120  can encode audio/video data  121 , and transmitter/receiver unit  126  can transmit the encoded data over communication channel  150  to sink device  160 . Transmitter/receiver unit  166  of sink device  160  receives the encoded data, and audio/video decoder  164  decodes the encoded data and outputs the decoded data via display  162  and speaker  163 . In this manner, the audio and video data being rendered by display  122  and speaker  123  can be simultaneously rendered by display  162  and speaker  163 . The audio data and video data may be arranged in frames, and the audio frames may be time-synchronized with the video frames when rendered. 
     Audio/video encoder  124  and audio/video decoder  164  may implement any number of audio and video compression standards, such as the ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10, Advanced Video Coding (AVC), or the newly emerging high efficiency video coding (HEVC) standard, sometimes called the H.265 standard. Many other types of proprietary or standardized compression techniques may also be used. Generally speaking, audio/video decoder  164  is configured to perform the reciprocal coding operations of audio/video encoder  124 . Although not shown in  FIG. 1A , in some aspects, A/V encoder  124  and A/V decoder  164  may each be integrated with an audio encoder and decoder, and may include appropriate MUX-DEMUX units, or other hardware and software, to handle encoding of both audio and video in a common data stream or separate data streams. 
     As will be described in more detail below, A/V encoder  124  may also perform other encoding functions in addition to implementing a video compression standard as described above. For example, A/V encoder  124  may add various types of metadata to A/V data  121  prior to A/V data  121  being transmitted to sink device  160 . In some instances, A/V data  121  may be stored on or received at source device  120  in an encoded form and thus not require further compression by A/V encoder  124 . 
     Although,  FIG. 1A  shows communication channel  150  carrying audio payload data and video payload data separately, it is to be understood that in some instances video payload data and audio payload data may be part of a common data stream. If applicable, MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, or other protocols such as the user datagram protocol (UDP). Audio/video encoder  124  and audio/video decoder  164  each may be implemented as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof. Each of audio/video encoder  124  and audio/video decoder  164  may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC). Thus, each of source device  120  and sink device  160  may comprise specialized machines configured to execute one or more of the techniques of this disclosure. 
     Display  122  and display  162  may comprise any of a variety of video output devices such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, a light emitting diode (LED) display, an organic light emitting diode (OLED) display, or another type of display device. In these or other examples, the displays  122  and  162  may each be emissive displays or transmissive displays. Display  122  and display  162  may also be touch displays such that they are simultaneously both input devices and display devices. Such touch displays may be capacitive, resistive, or other type of touch panel that allows a user to provide user input to the respective device. 
     Speaker  123  may comprise any of a variety of audio output devices such as headphones, a single-speaker system, a multi-speaker system, or a surround sound system. Additionally, although display  122  and speaker  123  are shown as part of source device  120  and display  162  and speaker  163  are shown as part of sink device  160 , source device  120  and sink device  160  may in fact be a system of devices. As one example, display  162  may be a television, speaker  163  may be a surround sound system, and decoder  164  may be part of an external box connected, either wired or wirelessly, to display  162  and speaker  163 . In other instances, sink device  160  may be a single device, such as a tablet computer or smartphone. In still other cases, source device  120  and sink device  160  are similar devices, e.g., both being smartphones, tablet computers, or the like. In this case, one device may operate as the source and the other may operate as the sink. These rolls may even be reversed in subsequent communication sessions. In still other cases, the source device may comprise a mobile device, such as a smartphone, laptop or tablet computer, and the sink device may comprise a more stationary device (e.g., with an AC power cord), in which case the source device may deliver audio and video data for presentation to a large crowd via the sink device. 
     Transmitter/receiver unit  126  and transmitter/receiver unit  166  may each include various mixers, filters, amplifiers and other components designed for signal modulation, as well as one or more antennas and other components designed for transmitting and receiving data. Communication channel  150  generally represents any suitable communication medium, or collection of different communication media, for transmitting video data from source device  120  to sink device  160 . Communication channel  150  is usually a relatively short-range communication channel, similar to Wi-Fi, Bluetooth, or the like. However, communication channel  150  is not necessarily limited in this respect, and may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines, or any combination of wireless and wired media. In other examples, communication channel  150  may even form part of a packet-based network, such as a wired or wireless local area network, a wide-area network, or a global network such as the Internet. Additionally, communication channel  150  may be used by source device  120  and sink device  160  to create a peer-to-peer link. Source device  120  and sink device  160  may communicate over communication channel  150  using a communications protocol such as a standard from the IEEE 802.11 family of standards. Source device  120  and sink device  160  may, for example, communicate according to the Wi-Fi Direct standard, such that source device  120  and sink device  160  communicate directly with one another without the use of an intermediary such as a wireless access points or so called hotspot. Source device  120  and sink device  160  may also establish a tunneled direct link setup (TLDS) to avoid or reduce network congestion. The techniques of this disclosure may at times be described with respect to Wi-Fi, but it is contemplated that aspects of these techniques may also be compatible with other communication protocols. By way of example and not limitation, the wireless communication between source device  120  and sink device may utilize orthogonal frequency division multiplexing (OFDM) techniques. A wide variety of other wireless communication techniques may also be used, including but not limited to time division multi access (TDMA), frequency division multi access (FDMA), code division multi access (CDMA), or any combination of OFDM, FDMA, TDMA and/or CDMA. WiFi Direct and TDLS are intended to setup relatively short-distance communication sessions. Relatively short distance in this context may refer to, for example, less than 70 meters, although in a noisy or obstructed environment the distance between devices may be even shorter, such as less than 35 meters. 
     In addition to decoding and rendering data received from source device  120 , sink device  160  can also receive user inputs from user input device  167 . User input device  167  may, for example, be a keyboard, mouse, trackball or track pad, touch screen, voice command recognition module, or any other such user input device. UIPM  168  formats user input commands received by user input device  167  into a data packet structure that source device  120  is capable of interpreting. Such data packets are transmitted by transmitter/receiver  166  to source device  120  over communication channel  150 . Transmitter/receiver unit  126  receives the data packets, and A/V control module  125  parses the data packets to interpret the user input command that was received by user input device  167 . Based on the command received in the data packet, A/V control module  125  can change the content being encoded and transmitted. In this manner, a user of sink device  160  can control the audio payload data and video payload data being transmitted by source device  120  remotely and without directly interacting with source device  120 . Examples of the types of commands a user of sink device  160  may transmit to source device  120  include commands for rewinding, fast forwarding, pausing, and playing audio and video data, as well as commands for zooming, rotating, scrolling, and so on. Users may also make selections, from a menu of options for example, and transmit the selection back to source device  120 . 
     Additionally, users of sink device  160  may be able to launch and control applications on source device  120 . For example, a user of sink device  160  may able to launch a photo editing application stored on source device  120  and use the application to edit a photo that is stored locally on source device  120 . Sink device  160  may present a user with a user experience that looks and feels like the photo is being edited locally on sink device  160  while in fact the photo is being edited on source device  120 . Using such a configuration, a device user may be able to leverage the capabilities of one device for use with several devices. For example, source device  120  may be a smartphone with a large amount of memory and high-end processing capabilities. A user of source device  120  may use the smartphone in all the settings and situations smartphones are typically used. When watching a movie, however, the user may wish to watch the movie on a device with a bigger display screen, in which case sink device  160  may be a tablet computer or even larger display device or television. When wanting to send or respond to email, the user may wish to use a device with a keyboard, in which case sink device  160  may be a laptop. In both instances, the bulk of the processing may still be performed by source device  120  (a smartphone in this example) even though the user is interacting with a sink device. In this particular operating context, due to the bulk of the processing being performed by source device  120 , sink device  160  may be a lower cost device with fewer resources than if sink device  160  were being asked to do the processing being done by source device  120 . Both the source device and the sink device may be capable of receiving user input (such as touch screen commands) in some examples, and the techniques of this disclosure may facilitate two way interaction by negotiating and or identifying the capabilities of the devices in any given session. 
     In some configuration, A/V control module  125  may be an operating system process being executed by the operating system of source device  125 . In other configurations, however, A/V control module  125  may be a software process of an application running on source device  120 . In such a configuration, the user input command may be interpreted by the software process, such that a user of sink device  160  is interacting directly with the application running on source device  120 , as opposed to the operating system running on source device  120 . By interacting directly with an application as opposed to an operating system, a user of sink device  160  may have access to a library of commands that are not native to the operating system of source device  120 . Additionally, interacting directly with an application may enable commands to be more easily transmitted and processed by devices running on different platforms. 
     Source device  120  can respond to user inputs applied at wireless sink device  160 . In such an interactive application setting, the user inputs applied at wireless sink device  160  may be sent back to the wireless display source over communication channel  150 . In one example, a reverse channel architecture, also referred to as a user interface back channel (UIBC) may be implemented to enable sink device  160  to transmit the user inputs applied at sink device  160  to source device  120 . The reverse channel architecture may include upper layer messages for transporting user inputs and lower layer frames for negotiating user interface capabilities at sink device  160  and source device  120 . The UIBC may reside over the Internet Protocol (IP) transport layer between sink device  160  and source device  120 . In this manner, the UIBC may be above the transport layer in the Open System Interconnection (OSI) communication model. In one example, the OSI communication includes seven layers (1—physical, 2—data link, 3—network, 4—transport, 5—session, 6—presentation, and 7—application). In this example, being above transport layer refers to layers 5, 6, and 7. To promote reliable transmission and in sequence delivery of data packets containing user input data, UIBC may be configured run on top of other packet-based communication protocols such as the transmission control protocol/internet protocol (TCP/IP) or the user datagram protocol (UDP). UDP and TCP can operate in parallel in the OSI layer architecture. TCP/IP can enable sink device  160  and source device  120  to implement retransmission techniques in the event of packet loss. 
     In some cases, there may be a mismatch between the user input interfaces located at source device  120  and sink device  160 . To resolve the potential problems created by such a mismatch and to promote a good user experience under such circumstances, user input interface capability negotiation may occur between source device  120  and sink device  160  prior to establishing a communication session or at various times throughout a communication session. As part of this negotiation process, source device  120  and sink device  160  can agree on a negotiated screen resolution. When sink device  160  transmits coordinate data associated with a user input, sink device  160  can scale coordinate data obtained from display  162  to match the negotiated screen resolution. In one example, if sink device  160  has a 1280×720 resolution and source device  120  has a 1600×900 resolution, the devices may, for example, use 1280×720 as their negotiated resolution. The negotiated resolution may be chosen based on a resolution of sink device  160 , although a resolution of source device  120  or some other resolution may also be used. In the example where the sink device of 1280×720 is used, sink device  160  can scale obtained x-coordinates by a factor of 1600/1280 prior to transmitting the coordinates to source device  120 , and likewise, sink device  160  can scale obtained y-coordinates by 900/720 prior to transmitting the coordinates to source device  120 . In other configurations, source device  120  can scale the obtained coordinates to the negotiated resolution. The scaling may either increase or decrease a coordinate range based on whether sink device  160  uses a higher resolution display than source device  120 , or vice versa. 
     Additionally, in some instances, the resolution at sink device  160  may vary during a communication session, potentially creating a mismatch between display  122  and display  162 . In order to improve the user experience and to ensure proper functionality, source/sink system  100  may implement techniques for reducing or preventing user interaction mismatch by implementing techniques for screen normalization. Display  122  of source device  120  and display  162  of sink device  160  may have different resolutions and/or different aspects ratios. Additionally, in some settings, a user of sink device  160  may have the ability to resize a display window for the video data received from source device  120  such that the video data received from source device  120  is rendered in a window that covers less than all of display  162  of sink device  160 . In another example setting, a user of sink device  160  may have the option of viewing content in either a landscape mode or a portrait mode, each of which has unique coordinates and different aspect ratios. In such situations, coordinates associated with a user input received at sink device  160 , such as the coordinate for where a mouse click or touch event occurs, may not able to be processed by source device  120  without modification to the coordinates. Accordingly, techniques of this disclosure may include mapping the coordinates of the user input received at sink device  160  to coordinates associated with source device  120 . This mapping is also referred to as normalization herein, and as will be explained in greater detail below, this mapping can be either sink-based or source-based. 
     User inputs received by sink device  160  can be received by UI module  167 , at the driver level for example, and passed to the operating system of sink device  160 . The operating system on sink device  160  can receive coordinates (x SINK , y SINK ) associated with where on a display surface a user input occurred. In this example, (x SINK , y SINK ) can be coordinates of display  162  where a mouse click or a touch event occurred. The display window being rendered on display  162  can have an x-coordinate length (L DW ) and a y-coordinate width (W DW ) that describe the size of the display window. The display window can also have an upper left corner coordinate (a DW , b DW ) that describes the location of the display window. Based on L DW , W DW , and the upper left coordinate (a DW , b DW ), the portion of display  162  covered by the display window can be determined. For example, an upper right corner of the display window can be located at coordinate (a DW +L DW , b DW ), a lower left corner of the display window can be located at coordinate (a DW , b DW +W DW ), and a lower right corner of the display window can be located at coordinate (a DW +L DW , b DW +W DW ). Sink device  160  can process an input as a UIBC input if the input is received at a coordinate within the display window. In other words, an input with associated coordinates (x SINK , y SINK ) can be processed as a UIBC input if the following conditions are met:
 
 a   DW   ≦x   SINK   ≦a   DW   +L   DW   (1)
 
 b   DW   ≦y   SINK   ≦b   DW   +W   DW   (2)
 
     After determining that a user input is a UIBC input, coordinates associated with the input can be normalized by UIPM  168  prior to being transmitted to source device  120 . Inputs that are determined to be outside the display window can be processed locally by sink device  160  as non-UIBC inputs. 
     As mentioned above, the normalization of input coordinates can be either sourced-based or sink-based. When implementing sink-based normalization, source device  120  can send a supported display resolution (L SRC , W SRC ) for display  122 , either with video data or independently of video data, to sink device  160 . The supported display resolution may, for example, be transmitted as part of a capability negotiation session or may be transmitted at another time during a communication session. Sink device  160  can determine a display resolution (L SINK , W SINK ) for display  162 , the display window resolution (L DW , W DW ) for the window displaying the content received from source device  120 , and the upper left corner coordinate (a DW , b DW ) for the display window. As described above, when a coordinate (x SINK , y SINK ) corresponding to a user input is determined to be within the display window, the operating system of sink device  160  can map the coordinate (x SINK , y SINK ) to source coordinates (x SRC , y SRC ) using conversion functions. Example conversion functions for converting (x SINK , y SINK ) to (x SRC , y SRC ) can be as follows:
 
 x   SRC =( x   SINK   −a   DW )*( L   SRC   /L   DW )  (3)
 
 y   SRC =( y   SINK   −b   DW )*( W   SRC   /W   DW )  (4)
 
     Thus, when transmitting a coordinate corresponding to a received user input, sink device  160  can transmit the coordinate (x SRC , y SRC ) for a user input received at (x SINK , y SINK ). As will be described in more detail below, coordinate (x SRC , y SRC ) may, for example, be transmitted as part of a data packet used for transmitting user input received at sink device  160  to source device  120  over the UIBC. Throughout other portions of this disclosure, where input coordinates are described as being included in a data packet, those coordinates can be converted to source coordinates as described above in instances where source/sink system  100  implements sink-based normalization. 
     When source/sink system  100  implements sourced-based normalization, for user inputs determined to by UIBC inputs as opposed to local inputs (i.e. within a display window as opposed to outside a display window), the calculations above can be performed at source device  120  instead of sink device  160 . To facilitate such calculations, sink device  160  can transmit to source device  120  values for L DW , W DW , and location information for the display window (e.g. a DW , b DW ), as well as coordinates for (x SINK , y SINK ). Using these transmitted values, source device  120  can determine values for (x SRC , y SRC ) according to equations 3 and 4 above. 
     In other implementations of sink-based normalization, sink device  160  can transmit coordinates (x DW , y DW ) for a user input that describe where within the display window a user input event occurs as opposed to where on display  162  the user input even occurs. In such an implementation, coordinates (x DW , y DW ) can be transmitted to source device  120  along with values for (L DW , W DW ). Based on these received values, source device  120  can determine (x SRC , y SRC ) according to the following conversion functions:
 
 x   SRC   =x   DW *( L   SRC   /L   DW )  (5)
 
 y   SRC   =y   DW *( W   SRC   /W   DW )  (6)
 
Sink device  160  can determine x DW  and y DW  based on the following functions:
 
 x   DW   =x   SINK   −a   DW   (7)
 
 y   DW   =y   SINK   −b   DW   (8)
 
     When this disclosure describes transmitting coordinates associated with a user input, in a data packet for example, the transmission of these coordinates may include sink-based or source-based normalization as described above, and/or may include any additional information necessary for performing the sink-based or source-based normalization. 
     The UIBC may be designed to transport various types of user input data, including cross-platform user input data. For example, source device  120  may run the iOS® operating system, while sink device  160  runs another operating system such as Android® or Windows®. Regardless of platform, UIPM  168  can encapsulate received user input in a form understandable to A/V control module  125 . A number of different types of user input formats may be supported by the UIBC so as to allow many different types of source and sink devices to exploit the protocol regardless of whether the source and sink devices operate on different platforms. Generic input formats may be defined, and platform specific input formats may both be supported, thus providing flexibility in the manner in which user input can be communicated between source device  120  and sink device  160  by the UIBC. 
     In the example of  FIG. 1A , source device  120  may comprise a smartphone, tablet computer, laptop computer, desktop computer, Wi-Fi enabled television, or any other device capable of transmitting audio and video data. Sink device  160  may likewise comprise a smartphone, tablet computer, laptop computer, desktop computer, Wi-Fi enabled television, or any other device capable of receiving audio and video data and receiving user input data. In some instances, sink device  160  may include a system of devices, such that display  162 , speaker  163 , UI device  167 , and A/V encoder  164  all parts of separate but interoperative devices. Source device  120  may likewise be a system of devices rather than a single device. 
     In this disclosure, the term source device is generally used to refer to the device that is transmitting audio/video data, and the term sink device is generally used to refer to the device that is receiving the audio/video data from the source device. In many cases, source device  120  and sink device  160  may be similar or identical devices, with one device operating as the source and the other operating as the sink. Moreover, these rolls may be reversed in different communication sessions. Thus, a sink device in one communication session may become a source device in a subsequent communication session, or vice versa. 
       FIG. 1B  is a block diagram illustrating an exemplary source/sink system  101  that may implement techniques of this disclosure. Source/sink system  101  includes source device  120  and sink device  160 , each of which may function and operate in the manner described above for  FIG. 1A . Source/sink system  101  further includes sink device  180 . In a similar manner to sink device  160  described above, sink device  180  may receive audio and video data from source device  120  and transmit user commands to source device  120  over an established UIBC. In some configurations, sink device  160  and sink device  180  may operate independently of one another, and audio and video data output at source device  120  may be simultaneously output at sink device  160  and sink device  180 . In alternate configurations, sink device  160  may be a primary sink device and sink device  180  may be a secondary sink device. In such an example configuration, sink device  160  and sink device  180  may be coupled, and sink device  160  may display video data while sink device  180  outputs corresponding audio data. Additionally, in some configurations, sink device  160  may output transmitted video data only while sink device  180  outputs transmitted audio data only. 
       FIG. 2  is a block diagram showing one example of a source device  220 . Source device  220  may be a device similar to source device  120  in  FIG. 1A  and may operate in the same manner as source device  120 . Source device  220  includes local display  222 , local speaker  223 , processors  231 , memory  232 , transport unit  233 , and wireless modem  234 . As shown in  FIG. 2 , source device  220  may include one or more processors (i.e. processor  231 ) that encode and/or decode A/V data for transport, storage, and display. The A/V data may for example be stored at memory  232 . Memory  232  may store an entire A/V file, or may comprise a smaller buffer that simply stores a portion of an A/V file, e.g., streamed from another device or source. Transport unit  233  may process encoded A/V data for network transport. For example, encoded A/V data may be processed by processor  231  and encapsulated by transport unit  233  into Network Access Layer (NAL) units for communication across a network. The NAL units may be sent by wireless modem  234  to a wireless sink device via a network connection. Wireless modem  234  may, for example, be a Wi-Fi modem configured to implement one of the IEEE 802.11 family of standards. 
     Source device  220  may also locally process and display A/V data. In particular display processor  235  may process video data to be displayed on local display  222 , audio processor  236  may process audio data for output on speaker  223 . 
     As described above with reference to source device  120  of  FIG. 1A , source device  220  may also receive user input commands from a sink device. In this manner, wireless modem  234  of source device  220  receives encapsulated data packets, such as NAL units, and sends the encapsulated data units to transport unit  233  for decapsulation. For instance, transport unit  233  may extract data packets from the NAL units, and processor  231  can parse the data packets to extract the user input commands. Based on the user input commands, processor  231  can adjust the encoded A/V data being transmitted by source device  220  to a sink device. In this manner, the functionality described above in reference to A/V control module  125  of  FIG. 1A  may be implemented, either fully or partially, by processor  231 . 
     Processor  231  of  FIG. 2  generally represents any of a wide variety of processors, including but not limited to one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), other equivalent integrated or discrete logic circuitry, or some combination thereof. Memory  232  of  FIG. 2  may comprise any of a wide variety of volatile or non-volatile memory, including but not limited to random access memory (RAM) such as synchronous dynamic random access memory (SDRAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, and the like, Memory  232  may comprise a computer-readable storage medium for storing audio/video data, as well as other kinds of data. Memory  232  may additionally store instructions and program code that are executed by processor  231  as part of performing the various techniques described in this disclosure. 
       FIG. 3  shows an example of a sink device  360 . Sink device  360  may be a device similar to sink device  160  in  FIG. 1A  and may operate in the same manner as sink device  160 . Sink device  360  includes one or more processors (i.e. processor  331 ), memory  332 , transport unit  333 , wireless modem  334 , display processor  335 , local display  362 , audio processor  336 , speaker  363 , and user input interface  376 . Sink device  360  receives at wireless modem  334  encapsulated data units sent from a source device. Wireless modem  334  may, for example, be a Wi-Fi modem configured to implement one more standards from the IEEE 802.11 family of standards. Transport unit  333  can decapsulate the encapsulated data units. For instance, transport unit  333  may extract encoded video data from the encapsulated data units and send the encoded A/V data to processor  331  to be decoded and rendered for output. Display processor  335  may process decoded video data to be displayed on local display  362 , and audio processor  336  may process decoded audio data for output on speaker  363 . 
     In addition to rendering audio and video data, wireless sink device  360  can also receive user input data through user input interface  376 . User input interface  376  can represent any of a number of user input devices included but not limited to a touch display interface, a keyboard, a mouse, a voice command module, gesture capture device (e.g., with camera-based input capturing capabilities) or any other of a number of user input devices. User input received through user input interface  376  can be processed by processor  331 . This processing may include generating data packets that include the received user input command in accordance with the techniques described in this disclosure. Once generated, transport unit  333  may process the data packets for network transport to a wireless source device over a UIBC. 
     Processor  331  of  FIG. 3  may comprise one or more of a wide range of processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), other equivalent integrated or discrete logic circuitry, or some combination thereof. Memory  332  of  FIG. 3  may comprise any of a wide variety of volatile or non-volatile memory, including but not limited to random access memory (RAM) such as synchronous dynamic random access memory (SDRAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, and the like, Memory  232  may comprise a computer-readable storage medium for storing audio/video data, as well as other kinds of data. Memory  332  may additionally store instructions and program code that are executed by processor  331  as part of performing the various techniques described in this disclosure. 
       FIG. 4  shows a block diagram of an example transmitter system  410  and receiver system  450 , which may be used by transmitter/receiver  126  and transmitter/receiver  166  of  FIG. 1A  for communicating over communication channel  150 . At transmitter system  410 , traffic data for a number of data streams is provided from a data source  412  to a transmit (TX) data processor  414 . Each data stream may be transmitted over a respective transmit antenna. TX data processor  414  formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream. 
     The coded data for each data stream may be multiplexed with pilot data using orthogonal frequency division multiplexing (OFDM) techniques. A wide variety of other wireless communication techniques may also be used, including but not limited to time division multi access (TDMA), frequency division multi access (FDMA), code division multi access (CDMA), or any combination of OFDM, FDMA, TDMA and/or CDMA. 
     Consistent with  FIG. 4 , the pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (e.g., symbol mapped) based on a particular modulation scheme (e.g., Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), M-PSK, or M-QAM (Quadrature Amplitude Modulation), where M may be a power of two) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions performed by processor  430  which may be coupled with memory  432 . 
     The modulation symbols for the data streams are then provided to a TX MIMO processor  420 , which may further process the modulation symbols (e.g., for OFDM). TX MIMO processor  420  can then provide N T  modulation symbol streams to N T  transmitters (TMTR)  422   a  through  422   t . In certain aspects, TX MIMO processor  420  applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted. 
     Each transmitter  422  may receive and process a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. N T  modulated signals from transmitters  422   a  through  422   t  are then transmitted from N T  antennas  424   a  through  424   t , respectively. 
     At receiver system  450 , the transmitted modulated signals are received by N R  antennas  452   a  through  452   r  and the received signal from each antenna  452  is provided to a respective receiver (RCVR)  454   a  through  454   r . Receiver  454  conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream. 
     A receive (RX) data processor  460  then receives and processes the N R  received symbol streams from N R  receivers  454  based on a particular receiver processing technique to provide N T  “detected” symbol streams. The RX data processor  460  then demodulates, deinterleaves and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by RX data processor  460  is complementary to that performed by TX MIMO processor  420  and TX data processor  414  at transmitter system  410 . 
     A processor  470  that may be coupled with a memory  472  periodically determines which pre-coding matrix to use. The reverse link message may comprise various types of information regarding the communication link and/or the received data stream. The reverse link message is then processed by a TX data processor  438 , which also receives traffic data for a number of data streams from a data source  436 , modulated by a modulator  480 , conditioned by transmitters  454   a  through  454   r , and transmitted back to transmitter system  410 . 
     At transmitter system  410 , the modulated signals from receiver system  450  are received by antennas  424 , conditioned by receivers  422 , demodulated by a demodulator  440 , and processed by a RX data processor  442  to extract the reserve link message transmitted by the receiver system  450 . Processor  430  then determines which pre-coding matrix to use for determining the beamforming weights then processes the extracted message. 
       FIG. 5A  is a block diagram illustrating an example message transfer sequence between a source device  520  and a sink device  560  as part of a capabilities negotiations session. Capability negotiation may occur as part of a larger communication session establishment process between source device  520  and sink device  560 . This session may, for example, be established with Wi-Fi Direct or TDLS as the underlying connectivity standard. After establishing the Wi-Fi Direct or TDLS session, sink device  560  can initiate a TCP connection with source device  520 . As part of establishing the TCP connection, a control port running a real time streaming protocol (RTSP) can be established to manage a communication session between source device  520  and sink device  560 . 
     Source device  520  may generally operate in the same manner described above for source device  120  of  FIG. 1A , and sink device  560  may generally operate in the same manner described above for sink device  160  of  FIG. 1A . After source device  520  and sink device  560  establish connectivity, source device  520  and sink device  560  may determine the set of parameters to be used for their subsequent communication session as part of a capability negotiation exchange. 
     Source device  520  and sink device  560  may negotiate capabilities through a sequence of messages. The messages may, for example, be real time streaming protocol (RTSP) messages. At any stage of the negotiations, the recipient of an RTSP request message may respond with an RTSP response that includes an RTSP status code other than RTSP OK, in which case, the message exchange might be retried with a different set of parameters or the capability negotiation session may be ended. 
     Source device  520  can send a first message (RTSP OPTIONS request message) to sink device  560  in order to determine the set of RTSP methods that sink device  560  supports. On receipt of the first message from source device  520 , sink device  560  can respond with a second message (RTSP OPTIONS response message) that lists the RTSP methods supported by sink  560 . The second message may also include a RTSP OK status code. 
     After sending the second message to source device  520 , sink device  560  can send a third message (RTSP OPTIONS request message) in order to determine the set of RTSP methods that source device  520  supports. On receipt of the third message from sink device  560 , source device  520  can respond with a fourth message (RTSP OPTIONS response message) that lists the RTSP methods supported by source device  520 . The fourth message can also include RTSP OK status code. 
     After sending the fourth message, source device  520  can send a fifth message (RTSP GET_PARAMETER request message) to specify a list of capabilities that are of interest to source device  520 . Sink device  560  can respond with a sixth message (an RTSP GET_PARAMETER response message). The sixth message may contain an RTSP status code. If the RTSP status code is OK, then the sixth message can also include response parameters to the parameter specified in the fifth message that are supported by sink device  560 . Sink device  560  can ignore parameters in the fifth message that sink device  560  does not support. 
     Based on the sixth message, source  520  can determine the optimal set of parameters to be used for the communication session and can send a seventh message (an RTSP SET_PARAMETER request message) to sink device  560 . The seventh message can contain the parameter set to be used during the communication session between source device  520  and sink device  560 . The seventh message can include the wfd-presentation-url that describes the Universal Resource Identifier (URI) to be used in the RTSP Setup request in order to setup the communication session. The wfd-presentation-url specifies the URI that sink device  560  can use for later messages during a session establishment exchange. The wfd-url0 and wfd-url1 values specified in this parameter can correspond to the values of rtp-port0 and rtp-port1 values in the wfd-client-rtp-ports in the seventh message. RTP in this instance generally refers to the real-time protocol which can run on top of the UDP. 
     Upon receipt of the seventh message, sink device  560  can respond with an eighth message with an RTSP status code indicating if setting the parameters as specified in the seventh message was successful. As mentioned above, the roles or source device and sink device may reverse or change in different sessions. The order of the messages that set up the communication session may, in some cases, define the device that operates as the source and define the device that operates as the sink. 
       FIG. 5B  is a block diagram illustrating another example message transfer sequence between a source device  560  and a sink device  520  as part of capabilities negotiations session. The message transfer sequence of  FIG. 5B  is intended provide a more detailed view of the transfer sequence described above for  FIG. 5A . In  FIG. 5B , message “1b. GET_PARAMETER RESPONSE” shows an example of a message that identifies a list of supported input categories (e.g. generic and HIDC) and a plurality of lists of supported input types. Each of the supported input categories of the list of supported input categories has an associated list of supported types (e.g. generic_cap_list and hidc_cap_list). In  FIG. 5B , message “2a. SET_PARAMETER REQUEST” is an example of a second message that identifies a second list of supported input categories (e.g. generic and HIDC), and a plurality of second lists of supported types. Each of the supported input categories of the second list of supported input categories has an associated second list of supported types (e.g. generic_cap_list and hidc_cap_list). Message “1b. GET_PARAMETER RESPONSE” identifies the input categories and input types supported by sink device  560 . Message “2a. SET_PARAMETER REQUEST” identifies input categories and input types supported by source device  520 , but it may not be a comprehensive list of all input categories and input types supported by source device  520 . Instead, message “2a. SET_PARAMETER REQUEST” may identify only those input categories and input types identified in message “1b. GET_PARAMETER RESPONSE” as being supported by sink device  560 . In this manner, the input categories and input types identified in message “2a. SET_PARAMETER REQUEST” may constitute a subset of the input categories and input types identified in message “1b. GET_PARAMETER RESPONSE.” 
       FIG. 6  is a conceptual diagram illustrating one example of a data packet that may be generated by a sink device and transmitted to a source device. Aspects of data packet  600  will be explained with reference to  FIG. 1A , but the techniques discussed may be applicable to additional types of source/sink systems. Data packet  600  may include a data packet header  610  followed by payload data  650 . Payload data  650  may additionally include one or more payload headers (e.g. payload header  630 ). Data packet  600  may, for example, be transmitted from sink device  160  of  FIG. 1A  to source device  120 , such that a user of sink device  160  can control audio/video data being transmitted by source device  120 . In such an instance, payload data  650  may include user input data received at sink device  160 . Payload data  650  may, for example, identify one or more user commands. Sink device  160  can receive the one or more user commands, and based on the received commands, can generate data packet header  610  and payload data  650 . Based on the content of data packet header  610  of data packet  600 , source device  120  can parse payload data  650  to identify the user input data received at sink device  160 . Based on the user input data contained in payload data  650 , source device  120  may alter in some manner the audio and video data being transmitted from source device  120  to sink device  160 . 
     As used in this disclosure, the terms “parse” and “parsing” generally refer to the process of analyzing a bitstream to extract data from the bitstream. Once extracted, the data can be processed by source device  120 , for example. Extracting data may, for example, include identifying how information in the bitstream is formatted. As will be described in more detail below, data packet header  610  may define a standardized format that is known to both source device  120  and sink device  160 . Payload data  650 , however, may be formatted in one of many possible ways. By parsing data packet header  610 , source device  120  can determine how payload data  650  is formatted, and thus, source device  120  can parse payload data  650  to extract from payload data  650  one or more user input commands. This can provide flexibility in terms of the different types of payload data that can be supported in source-sink communication. As will be described in more detail below, payload data  650  may also include one or more payload headers such as payload header  630 . In such instances, source device  120  may parse data packet header  610  to determine a format for payload header  630 , and then parse payload header  630  to determine a format for the remainder of payload data  650 . 
     Diagram  620  is a conceptual depiction of how data packet header  610  may be formatted. The numbers 0-15 in row  615  are intended to identify bit locations within data packet header  610  and are not intended to actually represent information contained within data packet header  610 . Data packet header  610  includes version field  621 , timestamp flag  622 , reserved field  623 , input category field  624 , length field  625 , and optional timestamp field  626 . 
     In the example of  FIG. 6 , version field  621  is a 3-bit field that may indicate the version of a particular communications protocol being implemented by sink device  160 . The value in version field  621  may inform source device  120  how to parse the remainder of data packet header  610  as well as how to parse payload data  650 . In the example of  FIG. 6 , version field  621  is a three-bit field, which would enable a unique identifier for eight different versions. In other examples, more or fewer bits may be dedicated to version field  621 . 
     In the example of  FIG. 6 , timestamp flag (T)  622  is a 1-bit field that indicates whether or not timestamp field  626  is present in data packet header  610 . Timestamp field  626  is a 16-bit field containing a timestamp based on multimedia data that was generated by source device  120  and transmitted to sink device  160 . The timestamp may, for example, be a sequential value assigned to frames of video by source device  120  prior to the frames being transmitted to sink device  160 . Timestamp flag  622  may, for example, include a “1” to indicate timestamp field  626  is present and may include a “0” to indicate timestamp field  626  is not present. Upon parsing data packet header  610  and determining that timestamp field  626  is present, source device  120  can process the timestamp included in timestamp field  626 . Upon parsing data packet header  610  and determining that timestamp field  626  is not present, source device  120  may begin parsing payload data  650  after parsing length field  625 , as no timestamp field is present in data packet header  610 . 
     If present, timestamp field  626  can include a timestamp to identify a frame of video data that was being displayed at wireless sink device  160  when the user input data of payload data  650  was obtained. The timestamp may, for example, have been added to the frame of video by source device  120  prior to source device  120  transmitting the frame of video to sink device  160 . Accordingly, source device  120  may generate a frame of video and embed in the video data of the frame, as metadata for example, a timestamp. Source device  120  can transmit the video frame, with the timestamp, to sink device  160 , and sink device  160  can display the frame of video. While the frame of video is being displayed by sink device  160 , sink device  160  can receive a user command from a user. When sink device  160  generates a data packet to transfer the user command to source device  120 , sink device  160  can include in timestamp field  626  the timestamp of the frame that was being displayed by sink device  160  when the user command was received. 
     Upon receiving data packet  600  with timestamp field  626  present in the header, wireless source device  120  may identify the frame of video being displayed at sink device  160  at the time the user input data of payload data  650  was obtained and process the user input data based on the content of the frame identified by the timestamp. For example, if the user input data is a touch command applied to a touch display or a click of a mouse pointer, source device  120  can determine the content of the frame being displayed at the time the user applied the touch command to the display or clicked the mouse. In some instances, the content of the frame may be needed to properly process the payload data. For example, a user input based on a user touch or a mouse click can be dependent on what was being shown on the display at the time of the touch or the click. The touch or click may, for example, correspond to an icon or menu option. In instances where the content of the display is changing, a timestamp present in timestamp field  626  can be used by source device  120  to match the touch or click to the correct icon or menu option. 
     Source device  120  may additionally or alternatively, compare the timestamp in timestamp field  626  to a timestamp being applied to a currently rendered frame of video. By comparing the timestamp of timestamp field  626  to a current timestamp, source device  120  can determine a round trip time. The round trip time generally corresponds to the amount of time that lapses from the point when a frame is transmitted by source device  120  to the point when a user input based on that frame is received back at source device  120  from sink device  160 . The round trip time can provide source device  120  with an indication of system latency, and if the round trip time is greater than a threshold value, then source device  120  may ignore the user input data contained in payload data  650  under the assumption the input command was applied to an outdated display frame. When the round trip time is less than the threshold, source device  120  may process the user input data and adjust the audio/video content being transmitted in response to the user input data. Thresholds may be programmable, and different types of devices (or different source-sink combinations) may be configured to define different thresholds for round trip times that are acceptable. 
     In the example of  FIG. 6 , reserved field  623  is an 8-bit field that does not include information used by source  120  in parsing data packet header  610  and payload data  650 . Future versions of a particular protocol (as identified in version field  621 ), however, may make use of reserved field  623 , in which case source device  120  may use information in reserved field  623  for parsing data packet header  610  and/or for parsing payload data  650 . Reserved field  623  in conjunction with version field  621  potentially provide capabilities for expanding and adding features to the data packet format without fundamentally altering the format and features already in use. 
     In the example of  FIG. 6 , input category field  624  is a 4-bit field to identify an input category for the user input data contained in payload data  650 . Sink device  160  may categorize the user input data to determine an input category. Categorizing user input data may, for example, be based on the device from which a command is received or based on properties of the command itself. The value of input category field  624 , possibly in conjunction with other information of data packet header  610 , identifies to source device  120  how payload data  650  is formatted. Based on this formatting, source device  120  can parse payload data  650  to determine the user input that was received at sink device  160 . 
     As input category  624 , in the example of  FIG. 6 , is 4 bits, sixteen different input categories could possibly be identified. One such input category may be a generic input format to indicate that the user input data of payload data  650  is formatted using generic information elements defined in a protocol being executed by both source device  120  and sink device  160 . A generic input format, as will be described in more detail below, may utilize generic information elements that allow for a user of sink device  160  to interact with source device  120  at the application level. 
     Another such input category may be a human interface device command (HIDC) format to indicate that the user input data of payload data  650  is formatted based on the type of input device used to receive the input data. Examples of types of devices include a keyboard, mouse, touch input device, joystick, camera, gesture capturing device (such as a camera-based input device), and remote control. Other types of input categories that might be identified in input category field  624  include a forwarding input format to indicate user data in payload data  650  did not originate at sink device  160 , or an operating system specific format, and a voice command format to indicate payload data  650  includes a voice command. 
     Length field  625  may comprise a 16-bit field to indicate the length of data packet  600 . The length may, for example, be indicated in units of 8-bits. As data packet  600  is parsed by source device  120  in words of 16 bits, data packet  600  can be padded up to an integer number of 16 bits. Based on the length contained in length field  625 , source device  120  can identify the end of payload data  650  (i.e. the end of data packet  600 ) and the beginning of a new, subsequent data packet. 
     The various sizes of the fields provided in the example of  FIG. 6  are merely intended to be explanatory, and it is intended that the fields may be implemented using different numbers of bits than what is shown in  FIG. 6 . Additionally, it is also contemplated that data packet header  610  may include fewer than all the fields discussed above or may use additional fields not discussed above. Indeed, the techniques of this disclosure may be flexible, in terms of the actual format used for the various data fields of the packets. 
     After parsing data packet header  610  to determine a formatting of payload data  650 , source device  120  can parse payload data  650  to determine the user input command contained in payload data  650 . Payload data  650  may have its own payload header (payload header  630 ) indicating the contents of payload data  650 . In this manner, source device  120  may parse payload header  630  based on the parsing of data packet header  610 , and then parse the remainder payload data  650  based on the parsing of the payload header  630 . 
     If, for example, input category field  624  of data packet header  610  indicates a generic input is present in payload data  650 , then payload data  650  can have a generic input format. Source device  120  can thus parse payload data  650  according to the generic input format. As part of the generic input format, payload data  650  can include a series of one or more input events with each input event having its own input event header. Table 1, below identifies the fields that may be included in an input header. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Field 
                 Size (Octet) 
                 Value 
               
               
                   
               
             
            
               
                 Generic IE ID 
                 1 
                 See Table 2 
               
               
                 Length 
                 2 
                 Length of the following fields in octets 
               
               
                 Describe 
                 Variable 
                 The details of the user inputs. See Tables 
               
               
                   
               
            
           
         
       
     
     The generic input event (IE) identification (ID) field identifies the generic input event identification for identifying an input type. The generic IE ID field may, for example, be one octet in length and may include an identification selected from Table 2 below. If, as in this example, the generic IE ID field is 8 bits, then 256 different types of inputs (identified 0-255) may be identifiable, although not all 256 identifications necessarily need an associated input type. Some of the 256 may be reserved for future use with future versions of whatever protocol is being implemented by sink device  160  and source device  120 . In Table 2, for instance, generic IE IDs 9-255 do not have associated input types but could be assigned input types in the future. 
     The length field in the input event header identifies the length of the describe field while the describe field includes the information elements that describe the user input. The formatting of the describe field may be dependent on the type of input identifies in the generic IE ID field. Thus, source device  120  may parse the contents of the describe field based on the input type identified in the generic IE ID field. Based on the length field of the input event header, source device  120  can determine the end of one input event in payload data  650  and the beginning of a new input event. As will be explained in more detail below, one user command may be described in payload data  650  as one or more input events. 
     Table 2 provides an example of input types, each with a corresponding generic IE ID that can be used for identifying the input type. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Generic IE ID 
                 INPUT TYPE 
               
               
                   
               
             
            
               
                 0 
                 Left Mouse Down/Touch Down 
               
               
                 1 
                 Left Mouse Up/Touch Up 
               
               
                 2 
                 Mouse Move/Touch Move 
               
               
                 3 
                 Key Down 
               
               
                 4 
                 Key Up 
               
               
                 5 
                 Zoom 
               
               
                 6 
                 Vertical Scroll 
               
               
                 7 
                 Horizontal Scroll 
               
               
                 8 
                 Rotate 
               
               
                 9-255 
                 Reserved 
               
               
                   
               
            
           
         
       
     
     The describe fields associated with each input type may have a different format. The describe fields of a LeftMouse Down/TouchDown event, a Left Mouse Up/Touch Up event, and Mouse Move/Touch Move event may, for example, include the information elements identified in Table 3 below, although other formats could also be used in other examples. 
     
       
         
           
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Field 
                 (Octet) 
                 Notes 
               
               
                   
               
             
            
               
                 Number of 
                 1 
                 Number of pointers of a multi-touch motion 
               
               
                 pointers (N) 
                   
                 event. When set to 1, it indicates a single-touch 
               
               
                   
                   
                 motion event. 
               
               
                 For i = 1: N { 
               
               
                 Pointer ID 
                 1 
                 The identification number of this pointer. The 
               
               
                   
                   
                 value lies in [0, 1, . . . ] 
               
               
                 X-coordinate 
                 2 
                 X-coordinate for the event normalized with 
               
               
                   
                   
                 respect to a negotiated resolution of a video 
               
               
                   
                   
                 stream between sink device and source device. 
               
               
                 Y-coordinate} 
                 2 
                 Y-coordinate for the event normalized with 
               
               
                   
                   
                 respect to a negotiated resolution of a video 
               
               
                   
                   
                 stream between sink device and source device. 
               
               
                   
               
            
           
         
       
     
     The number of pointers may identify the number of touches or mouse clicks associated with an input event. Each pointer may have a unique pointer ID. If, for example, a multi-touch event includes a three finger touch, then the input event might have three pointers, each with a unique pointer ID. Each pointer (i.e. each finger touch) may have a corresponding x-coordinate and y-coordinate corresponding to where the touch occurred. 
     A single user command may be described as a series of input events. For example, if a three-finger swipe is a command to close an application, the three finger swipe may be described in payload data  650  as a touch down event with three pointers, a touch move event with three pointers, and a touch up event with three pointers. The three pointers of the touch down event may have the same pointer IDs as the three pointers of the touch move event and touch up event. Source device  120  can interpret the combination of those three input events as a three finger swipe. 
     The describe fields of a Key Down event or a Key Up event may, for example, include the information elements identified in Table 4 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Field 
                 (Octet) 
                 Notes 
               
               
                   
               
             
            
               
                 Reserved 
                 1 
                 Reserved 
               
               
                 Key code 
                 2 
                 The key code of the first key down or up event. The 
               
               
                 1 (ASCII) 
                   
                 basic/extended ASCII code uses the lower one 
               
               
                   
                   
                 byte. The higher one byte is reserved for future 
               
               
                   
                   
                 ASCII compatible key code 
               
               
                 Key code 
                 2 
                 The key code for the second key down or up 
               
               
                 2 (ASCII) 
                   
                 event. The basic/extended ASCII code uses the 
               
               
                   
                   
                 lower one byte. The higher one byte is reserved for 
               
               
                   
                   
                 future ASCII compatible key code. 
               
               
                   
               
            
           
         
       
     
     The describe field of a zoom event may, for example, include the information elements identified in Table 5 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Field 
                 (Octet) 
                 Notes 
               
               
                   
               
             
            
               
                 X 
                 2 
                 The reference X-coordinate for the zoom operation 
               
               
                   
                   
                 normalized with respect to with respect to a 
               
               
                   
                   
                 negotiated resolution of a video stream between sink 
               
               
                   
                   
                 device and source device. 
               
               
                 Y 
                 2 
                 The reference Y-coordinate for the zoom operation 
               
               
                   
                   
                 normalized with respect to with respect to a 
               
               
                   
                   
                 negotiated resolution of a video stream between sink 
               
               
                   
                   
                 device and source device. 
               
               
                 Integer 
                 1 
                 The unsigned integer portion of the number of times 
               
               
                 times to 
                   
                 to zoom 
               
               
                 zoom 
               
               
                 Fraction 
                 1 
                 The fraction portion of the number of times to zoom 
               
               
                 times to 
               
               
                 zoom 
               
               
                   
               
            
           
         
       
     
     The describe field of a horizontal scroll event or a vertical scroll event may, for example, include the information elements identified in Table 6 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                   
                 Size 
                   
               
               
                 Field 
                 (Octet) 
                 Notes 
               
               
                   
               
             
            
               
                 Amount to 
                 2 
                 Number of pixels to scroll normalized with respect 
               
               
                 scroll 
                   
                 to a negotiated resolution of a video stream 
               
               
                   
                   
                 between sink device and source device. A negative 
               
               
                   
                   
                 number can indicate to scroll right, and a positive 
               
               
                   
                   
                 number can indicate to scroll left 
               
               
                   
               
            
           
         
       
     
     The above examples have shown some exemplary ways that the payload data might be formatted for a generic input category. If input category field  624  of data packet header  610  indicates a different input category, such as a forwarded user input, then payload data  650  can have a different input format. With a forwarded user input, sink device  160  may receive the user input data from a third party device and forward the input to source device  120  without interpreting the user input data. Source device  120  can thus parse payload data  650  according to the forwarded user input format. For example, payload header  630  of payload data  650  may include a field to identify the third party device from which the user input was obtained. The field may, for example, include an internet protocol (IP) address of the third party device, MAC address, a domain name, or some other such identifier. Source device  120  can parse the remainder of the payload data based on the identifier of the third party device. 
     Sink device  160  can negotiate capabilities with the third party device via a series of messages. Sink device  160  can then transmit a unique identifier of the third party device to source device  120  as part of establishing a communication session with source device  120  as part of a capability negotiation process. Alternatively, sink device  160  may transmit information describing the third-party device to source device  120 , and based on the information, source device  120  can determine a unique identifier for the third-party device. The information describing the third party device may, for example, include information to identify the third-party device and/or information to identify capabilities of the third-party device. Regardless of whether the unique identifiers is determined by source device  120  or sink device  160 , when sink device  160  transmits data packets with user input obtained from the third part device, sink device  160  can include the unique identifier in the data packet, in a payload header for example, so that source device  120  can identify the origin of the user input. 
     If input category field  624  of data packet header  610  indicates yet a different input category, such as a voice command, then payload data  650  can have yet a different input format. For a voice command, payload data  650  may include coded audio. The codec for encoding and decoding the audio of the voice command can be negotiated between source device  120  and sink device  160  via a series of messages. For transmitting a voice command, timestamp field  626  may include a speech-sampling time value. In such an instance, timestamp flag  622  may be set to indicate a timestamp is present, but instead of a timestamp as described above, timestamp field  626  may include a speech-sampling time value for the encoded audio of payload data  650 . 
     In some examples, a voice command may be transmitted as a generic command as described above, in which case input category field  624  may be set to identify the generic command format, and one of the reserved generic IE IDs may be assigned to voice commands. If the voice command is transmitted as a generic command, then a speech sampling rate may be present in timestamp field  626  of data packet header  610  or may be present in payload data  650 . 
     For captured voice command data, the voice data can be encapsulated in multiple ways. For example, the voice command data can be encapsulated using RTP which can provide the payload type to identify the codec and timestamp, with the timestamp being used to identify the sampling rate. The RTP data can be encapsulated using the generic user input format described above, either with or without the optional timestamp. Sink device  160  can transmit the generic input data that carries the voice command data to source device  120  using TPC/IP. 
     As discussed previously, when coordinates are included as part of a data packet such as data packet  600 , in payload data  650  for example, the coordinates may correspond to coordinates scaled based on a negotiated resolution, display window coordinates, normalized coordinates, or coordinates associated with a sink display. In some instances, additional information, may be included, either in the data packet or transmitted separately, for use by a source device to normalize coordinates received in the data packet. 
     Regardless of the input category for a particular data packet the data packet header may be an application layer packet header, and the data packet may be transmitted over TCP/IP. TCP/IP can enable sink device  160  and source device  120  to perform retransmission techniques in the event of packet loss. The data packet may be sent from sink device  160  to source device  120  to control audio data or video data of source device  120  or for other purposes such as to control an application running on source device  120 . 
       FIG. 7A  is a flowchart of an example method of negotiating capabilities between a sink device and a source device. The illustrated example method may be performed by sink device  160  ( FIG. 1A ) or  360  ( FIG. 3 ). In some examples, a computer-readable storage medium (e.g., memory  332 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  331 ) to perform one or more of the illustrated steps in one or more of the flow charts described herein. 
     The method of  FIG. 7A  includes sink device  160  receiving from the source device  120  a first message ( 701 ). The message may, for example, comprise a get parameter request. In response to the first message, sink device  160  may send a second message to source device  120  ( 703 ). The second message may, for example, comprise a get parameter response that identifies a first list of supported input categories and a plurality of first lists of supported types, wherein each of the supported input categories of the first list of supported input categories has an associated first list of supported types. The supported input categories may, for example, correspond to the same categories used for input category field  624  of  FIG. 6 . Table 2 above represents one example of supported types for a particular input category (generic inputs in this example). Sink device  160  may receive from source device  120 , a third message ( 705 ). The third message may, for example, comprise a set parameter request, wherein the set parameter request identifies a port for communication, a second list of supported input categories, and a plurality of second lists of supported types, with each of the supported input categories of the second list of supported input categories having an associated second list of supported types, and each of the supported types of the second lists including a subset of the types of the first lists. Sink device  160  can transmit to source device  120  a fourth message ( 707 ). The fourth message may, for example, comprise a set parameter response to confirm that the types of the second lists have been enabled. Sink device  160  can receive from source device  120  a fifth message ( 709 ). The fifth message may, for example, comprise a second set parameter request that indicates that a communication channel between the source device  120  and sink device  160  has been enabled. The communication channel may, for example, comprise a user input back channel (UIBC). Sink device  160  can transmit to source device  120  a sixth message ( 711 ). The sixth message may, for example, comprise a second set parameter response that confirms receipt of the second set parameter request by sink device  160 . 
       FIG. 7B  is a flowchart of an example method of negotiating capabilities between a sink device and a source device. The illustrated example method may be performed by source device  120  ( FIG. 1A ) or  220  ( FIG. 2 ). In some examples, a computer-readable storage medium (e.g., memory  232 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  231 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 7B  includes source device  120  transmitting to sink device  160  a first message ( 702 ). The first message may, for example, comprise a get parameter request. Source device  120  can receive a second message from sink device  160  ( 704 ). The second message may, for example, comprise a get parameter response that identifies a first list of supported input categories and a plurality of first lists of supported types, wherein each of the supported input categories of the first list of supported input categories has an associated first list of supported types. Source device  120  may transmit to sink device  160 , a third message ( 706 ). The third message may, for example, comprise a set parameter request that identifies a port for communication, a second list of supported input categories, and a plurality of second lists of supported types, with each of the supported input categories of the second list of supported input categories having an associated second list of supported types, and each of the supported types of the second lists including a subset of the types of the first lists. Source device  120  can receive from sink device  160  a fourth message ( 708 ). The fourth message may, for example, comprise a set parameter response to confirm that the types of the second lists have been enabled. Source device  120  can transmit to sink device  160  a fifth message ( 710 ). The fifth message may, for example, comprise a second set parameter request that indicates that a communication channel between the source device  120  and sink device  160  has been enabled. The communication channel may, for example, comprise a user input back channel (UIBC). Source device  120  can receive from sink device  160  a sixth message ( 712 ). The sixth message may, for example, comprise a second set parameter response that confirms receipt of the second set parameter request by sink device  160 . 
       FIG. 8A  is a flow chart of an example method of transmitting user input data from a wireless sink device to a wireless source device in accordance with this disclosure. The illustrated example method may be performed by sink device  160  ( FIG. 1A ) or  360  ( FIG. 3 ). In some examples, a computer-readable storage medium (e.g., memory  332 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  331 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 8A  includes obtaining user input data at a wireless sink device, such as wireless sink device  160  ( 801 ). The user input data may be obtained through a user input component of wireless sink device  160  such as, for example, user input interface  376  shown in relation to wireless sink device  360 . Additionally, sink device  160  may categorize the user input data as, for example, generic, forwarded, or operating system specific. Sink device  160  may then generate a data packet header based on the user input data ( 803 ). The data packet header can be an application layer packet header. The data packet header may comprise, among other fields, a field to identify an input category corresponding to the user input data. The input category may comprise, for example, a generic input format or a human interface device command. Sink device  160  may further generate a data packet ( 805 ), where the data packet comprises the generated data packet header and payload data. In one example, payload data may include received user input data and may identify one or more user commands. Sink device  160  may then transmit the generated data packet ( 807 ) to the wireless source device (e.g., source device  120  of  FIG. 1A or 220  of  FIG. 2 ). Sink device  160  may comprise components that allow transfer of data packets, including transport unit  333  and wireless modem  334  as shown in  FIG. 3 , for example. Sink device  160  may transfer the data packet over TCP/IP. 
       FIG. 8B  is a flow chart of an example method of receiving user input data from a wireless sink device at a wireless source device in accordance with this disclosure. The illustrated example method may be performed by source device  120  ( FIG. 1A ) or  220  ( FIG. 2 ). In some examples, a computer-readable storage medium (e.g., memory  232 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  231 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 8B  includes receiving a data packet ( 802 ), where the data packet may comprise, among other things, a data packet header and payload data. Payload data may include, for example, user input data. Source device  120  may comprise communications components that allow transfer of data packets, including transport unit  233  and wireless modem  234 , for example as shown in reference to  FIG. 2 . Source device  120  may then parse the data packet header ( 804 ) included in the data packet, to determine an input category associated with the user input data contained in the payload data. Source device  120  may process the payload data based on the determined input category ( 806 ). The data packets described with reference to  FIGS. 8A and 8B  may generally take the form of the data packets described with reference to  FIG. 6  and may be used to control audio/video data and applications at a source device. 
       FIG. 9A  is a flow chart of an example method of transmitting user input data from a wireless sink device to a wireless source device in accordance with this disclosure. The illustrated example method may be performed by sink device  160  ( FIG. 1A ) or  360  ( FIG. 3 ). In some examples, a computer-readable storage medium (e.g., memory  332 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  331 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 9A  includes obtaining user input data at a wireless sink device such as wireless sink device  160  ( 901 ). The user input data may be obtained through a user input component of wireless sink device  160  such as, for example, user input interface  376  shown with reference to  FIG. 3 . Sink device  160  may then generate payload data ( 903 ), where the payload data may describe the user input data. In one example, payload data may include received user input data and may identify one or more user commands. Sink device  160  may further generate a data packet ( 905 ), where the data packet comprises a data packet header and the generated payload data. Sink device  160  may then transmit the generated data packet ( 907 ) to the wireless source device (e.g., source device  120  of  FIG. 1A or 220  of  FIG. 2 ). Sink device  160  may comprise components that allow transfer of data packets, such as transport unit  333  and wireless modem  334 , for example. The data packet can be transmitted to a wireless source device over TCP/IP. 
       FIG. 9B  is a flow chart of an example method of receiving user input data from a wireless sink device at a wireless source device in accordance with this disclosure. The illustrated example method may be performed by source device  120  ( FIG. 1A ) or  220  ( FIG. 2 ). In some examples, a computer-readable storage medium (e.g., memory  232 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  231 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 9B  includes receiving a data packet from sink device  360  ( 902 ), where the data packet may comprise, among other things, a data packet header and payload data. In one example, payload data may comprise, for example, data describing details of a user input such as input type value. Source device  120  may comprise communications components that allow transfer of data packets, including transport unit  233  and wireless modem  234 , for example as shown with reference to  FIG. 2 . Source device  120  may then parse the data packet ( 904 ) to determine an input type value in an input type field in the payload data. Source device  120  may process the data describing details of the user input based on the determined input type value ( 906 ). The data packets described with reference to  FIGS. 9A and 9B  may generally take the form of the data packets described with reference to  FIG. 6 . 
       FIG. 10A  is a flow chart of an example method of transmitting user input data from a wireless sink device to a wireless source device in accordance with this disclosure. The illustrated example method may be performed by sink device  160  ( FIG. 1A ) or  360  ( FIG. 3 ). In some examples, a computer-readable storage medium (e.g., memory  332 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  331 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 10A  includes obtaining user input data at a wireless sink device, such as wireless sink device  160  ( 1001 ). The user input data may be obtained through a user input component of wireless sink device  160  such as, for example, user input interface  376  as shown with reference to  FIG. 3 . Sink device  160  may then generate a data packet header based on the user input ( 1003 ). The data packet header may comprise, among other fields, a timestamp flag (e.g., a 1-bit field) to indicate if a timestamp field is present in the data packet header. The timestamp flag may, for example, include a “1” to indicate timestamp field is present and may include a “0” to indicate timestamp field is not present. The timestamp field may be, for example, a 16-bit field containing a timestamp generated by source device  120  and added to video data prior to transmission. Sink device  160  may further generate a data packet ( 1005 ), where the data packet comprises the generated data packet header and payload data. In one example, payload data may include received user input data and may identify one or more user commands. Sink device  160  may then transmit the generated data packet ( 1007 ) to the wireless source device (e.g., source device  120  of  FIG. 1A or 220  of  FIG. 2 ). Sink device  160  may comprise components that allow transfer of data packets, including transport unit  333  and wireless modem  334 , for example as shown in reference to  FIG. 3 . The data packet can be transmitted to a wireless source device over TCP/IP. 
       FIG. 10B  is a flow chart of an example method of receiving user input data from a wireless sink device at a wireless source device in accordance with this disclosure. The illustrated example method may be performed by source device  120  ( FIG. 1A ) or  220  ( FIG. 2 ). In some examples, a computer-readable storage medium (e.g., memory  232 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  231 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 10B  includes receiving a data packet from wireless sink device  160  ( 1002 ), where the data packet may comprise, among other things, a data packet header and payload data. Payload data may include, for example, user input data. Source device  120  may comprise communications components that allow transfer of data packets, including transport unit  233  and wireless modem  234 , for example as shown in reference to  FIG. 2 . Source device  120  may then parse the data packet header ( 1004 ) included in the data packet. Source device  120  may determine if a timestamp field is present in the data packet header ( 1006 ). In one example, Source device  120  may make the determination based on a timestamp flag value included in the data packet header. If the data packet header includes a timestamp field, Source device  120  may process the payload data based on a timestamp that is in the timestamp field ( 1008 ). The data packets described with reference to  FIGS. 10A and 10B  may generally take the form of the data packets described with reference to  FIG. 6  and may be used to control audio/video data at a source device. 
       FIG. 11A  is a flow chart of an example method of transmitting user input data from a wireless sink device to a wireless source device in accordance with this disclosure. The illustrated example method may be performed by sink device  160  ( FIG. 1A ) or  360  ( FIG. 3 ). In some examples, a computer-readable storage medium (e.g., memory  332 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  331 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 11A  includes obtaining user input data at a wireless sink device, such as wireless sink device  160  ( 1101 ). The user input data may be obtained through a user input component of wireless sink device  160  such as, for example, user input interface  376  shown in reference to  FIG. 3 . Sink device  160  may then generate a data packet header based on the user input ( 1103 ). The data packet header may comprise, among other fields, a timestamp field. The timestamp field may comprise, for example, a 16-bit field containing a timestamp based on multimedia data that was generated by wireless source device  120  and transmitted to wireless sink device  160 . The timestamp may have been added to the frame of video data by wireless source device  120  prior to being transmitted to the wireless sink device. The timestamp field may, for example, identify a timestamp associated with a frame of video data being displayed at wireless sink device  160  at the time the user input data was captured. Sink device  160  may further generate a data packet ( 1105 ), where the data packet comprises the generated data packet header and payload data. In one example, payload data may include received user input data and may identify one or more user commands. Sink device  160  may then transmit the generated data packet ( 1107 ) to the wireless source device (e.g., source device  120  of  FIG. 1A or 220  of  FIG. 2 ). Sink device  160  may comprise components that allow transfer of data packets, including transport unit  333  and wireless modem  334 , for example as shown in reference to  FIG. 3 . The data packet can be transmitted to a wireless source device over TCP/IP. 
       FIG. 11B  is a flow chart of an example method of receiving user input data from a wireless sink device at a wireless source device in accordance with this disclosure. The illustrated example method may be performed by source device  120  ( FIG. 1A ) or  220  ( FIG. 2 ). In some examples, a computer-readable storage medium (e.g., memory  232 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  231 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 11B  includes receiving a data packet from a wireless sink device, such as wireless sink device  160  ( 1102 ), where the data packet may comprise, among other things, a data packet header and payload data. Payload data may include, for example, user input data. Source device  120  may comprise communications components that allow transfer of data packets, including transport unit  233  and wireless modem  234 , for example as shown in reference to  FIG. 2 . Source device  120  may then identify a timestamp field in the data packet header ( 1104 ). Source device  120  may process the payload data based on a timestamp that is in the timestamp field ( 1106 ). As part of processing the payload data, based on the timestamp, source device  120  may identify a frame of video data being displayed at the wireless sink device at the time the user input data was obtained and interpret the payload data based on content of the frame. As part of processing the payload data based on the timestamp, source device  120  may compare the timestamp to a current timestamp for a current frame of video being transmitted by source device  120  and may perform a user input command described in the payload data in response to a time difference between the timestamp and the current timestamp being less than a threshold value, or not perform a user input command described in the payload data in response to a time difference between the timestamp and the current timestamp being greater than a threshold value. The data packets described with reference to  FIGS. 11A and 11B  may generally take the form of the data packets described with reference to  FIG. 6  and may be used to control audio/video data at a source device. 
       FIG. 12A  is a flow chart of an example method of transmitting user input data from a wireless sink device to a wireless source device in accordance with this disclosure. The illustrated example method may be performed by sink device  160  ( FIG. 1A ) or  360  ( FIG. 3 ). In some examples, a computer-readable storage medium (e.g., memory  332 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  331 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 12A  includes obtaining user input data at a wireless sink device, such as wireless sink device  160  ( 1201 ). In one example, the user input data may be voice command data, which may be obtained through a user input component of wireless sink device  160  such as, for example, a voice command recognition module included in user input interface  376  in  FIG. 3 . Sink device  160  may generate a data packet header based on the user input ( 1203 ). Sink device  160  may also generate payload data ( 1205 ), where the payload data may comprise the voice command data. In one example, payload data may also include received user input data and may identify one or more user commands. Sink device  160  may further generate a data packet ( 1207 ), where the data packet comprises the generated data packet header and payload data. Sink device  160  may then transmit the generated data packet ( 1209 ) to the wireless source device (e.g., source device  120  of  FIG. 1A or 220  of  FIG. 2 ). Sink device  160  may comprise components that allow transfer of data packets, including transport unit  333  and wireless modem  334 , for example as shown in reference to  FIG. 3 . The data packet can be transmitted to a wireless source device over TCP/IP. 
       FIG. 12B  is a flow chart of an example method of receiving user input data from a wireless sink device at a wireless source device in accordance with this disclosure. The illustrated example method may be performed by source device  120  ( FIG. 1A ) or  220  ( FIG. 2 ). In some examples, a computer-readable storage medium (e.g., memory  232 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  231 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 12B  includes receiving a data packet ( 1202 ), where the data packet may comprise, among other things, a data packet header and payload data. Payload data may include, for example, user input data such as voice command data. Source device  120  may comprise communications components that allow transfer of data packets, including transport unit  233  and wireless modem  234 , for example as shown in reference to  FIG. 2 . Source device  120  may then parse the payload data ( 1204 ) included in the data packet, to determine if the payload data comprises voice command data. The data packets described with reference to  FIGS. 12A and 12B  may generally take the form of the data packets described with reference to  FIG. 6  and may be used to control audio/video data at a source device. 
       FIG. 13A  is a flow chart of an example method of transmitting user input data from a wireless sink device to a wireless source device in accordance with this disclosure. The illustrated example method may be performed by sink device  160  ( FIG. 1A ) or  360  ( FIG. 3 ). In some examples, a computer-readable storage medium (e.g., memory  332 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  331 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 13A  includes obtaining user input data at a wireless sink device, such as wireless sink device  160  ( 1301 ). In one example, the user input data may be a multi-touch gesture, which may be obtained through a user input component of wireless sink device  160  such as, for example, UI  167  or user input interface  376  of  FIG. 3 . In one example, the multi-touch gesture may comprise a first touch input and a second touch input. Sink device  160  may generate a data packet header based on the user input ( 1303 ). Sink device  160  may also generate payload data ( 1305 ), where the payload data may associate user input data for the first touch input event with a first pointer identification and user input data for the second touch input event with a second pointer identification. Sink device  160  may further generate a data packet ( 1307 ), where the data packet comprises the generated data packet header and payload data. Sink device  160  may then transmit the generated data packet ( 1309 ) to the wireless source device (e.g., source device  120  of  FIG. 1A or 220  of  FIG. 2 ). Sink device  160  may comprise components that allow transfer of data packets, including transport unit  333  and wireless modem  334 , for example as shown in reference to  FIG. 3 . The data packet can be transmitted to a wireless source device over TCP/IP. 
       FIG. 13B  is a flow chart of an example method of receiving user input data from a wireless sink device at a wireless source device in accordance with this disclosure. The illustrated example method may be performed by source device  120  ( FIG. 1A ) or  220  ( FIG. 2 ). In some examples, a computer-readable storage medium (e.g., memory  232 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  231 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 13B  includes receiving a data packet ( 1302 ), where the data packet may comprise, among other things, a data packet header and payload data. Payload data may include, for example, user input data such as multi-touch gesture. Source device  120  may comprise communications components that allow transfer of data packets, including transport unit  233  and wireless modem  234 , for example as shown in  FIG. 2 . Source device  120  may then parse the payload data ( 1304 ) included in the data packet, to identify user input data included in the payload data. In one example, the identified data may include user input data for a first touch input event with a first pointer identification and user input data for a second touch input event with a second pointer identification. Source device  120  may then interpret the user input data for the first touch input event and the user input data for the second touch input event as a multi-touch gesture ( 1306 ). The data packets described with reference to  FIGS. 13A and 13B  may generally take the form of the data packets described with reference to  FIG. 6  and may be used to control audio/video data at a source device. 
       FIG. 14A  is a flow chart of an example method of transmitting user input data from a wireless sink device to a wireless source device in accordance with this disclosure. The illustrated example method may be performed by sink device  160  (FIG.  1 A) or  360  ( FIG. 3 ). In some examples, a computer-readable storage medium (e.g., memory  332 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  331 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 14A  includes obtaining user input data at wireless sink device  360  from an external device ( 1401 ). In one example, the external device may be a third party device connected to the sink device. Sink device  160  may generate a data packet header based on the user input ( 1403 ). In one example, the data packet header may identify the user input data as forwarded user input data. Sink device  160  may also generate payload data ( 1405 ), where the payload data may comprise the user input data. Sink device  160  may further generate a data packet ( 1407 ), where the data packet may comprise the generated data packet header and payload data. Sink device  160  may then transmit the generated data packet ( 1409 ) to the wireless source device (e.g., source device  120  of  FIG. 1A or 220  of  FIG. 2 ). Sink device  160  may comprise components that allow transfer of data packets, including transport unit  333  and wireless modem  334 , for example as shown with reference to  FIG. 3 . The data packet can be transmitted to a wireless source device over TCP/IP. 
       FIG. 14B  is a flow chart of an example method of receiving user input data from a wireless sink device at a wireless source device in accordance with this disclosure. The illustrated example method may be performed by source device  120  ( FIG. 1A ) or  220  ( FIG. 2 ). In some examples, a computer-readable storage medium (e.g., memory  232 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  231 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 14B  includes receiving a data packet ( 1402 ), where the data packet may comprise, among other things, a data packet header and payload data. Payload data may include, for example, user input data such as a forwarded user input command indicating user input data was forwarded from a third party device. Source device  120  may comprise communications components that allow transfer of data packets, including transport unit  233  and wireless modem  234 , for example as shown in reference to  FIG. 2 . Source device  120  may then parse the data packet header and may determine that the payload data comprises a forwarded user input command ( 1404 ). Source device  120  may then parse the payload data ( 1406 ) included in the data packet, to identify an identification associated with the third party device corresponding to the forwarded user input command. Source device  120  may then process the payload data based on the identified identification of the third party device ( 1408 ). The data packets described with reference to  FIGS. 14A and 14B  may generally take the form of the data packets described with reference to  FIG. 6  and may be used to control audio/video data at a source device. 
       FIG. 15A  is a flow chart of an example method of transmitting user data from a wireless sink device to a wireless source device in accordance with this disclosure. The illustrated example method may be performed by sink device  160  ( FIG. 1A ) or  360  ( FIG. 3 ). In some examples, a computer-readable storage medium (e.g., memory  332 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  331 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 15A  includes obtaining user input data at the wireless sink device ( 1501 ). The user input data can have associated coordinate data. The associated coordinate data may, for example, corresponds to a location of a mouse click event or a location of a touch event. Sink device  160  may then normalize the associated coordinate data to generate normalized coordinate data ( 1503 ). Sink device  160  may then generate a data packet that includes the normalized coordinate data ( 1505 ). Normalizing the coordinate data can include scaling the associated coordinate data based on a ratio of the resolution of a display window and a resolution of the display of the source, such as display  22  of source device  120 . The resolution of the display window can be determined by sink device  160 , and the resolution of the display of the source device can be received from source device  120 . Sink device  160  may then transmit the data packet with the normalized coordinates to wireless source device  120  ( 1507 ). As part of the method of  FIG. 15A , sink device  160  may also determine if the associated coordinate data is within a display window for content being received from the wireless source device, and for example, process a user input locally if the associated coordinate data is outside the display window, or otherwise normalize the coordinates as described if the input is within the display window. 
       FIG. 15B  is a flow chart of an example method of receiving user input data from a wireless sink device at a wireless source device in accordance with this disclosure. The illustrated example method may be performed by source device  120  ( FIG. 1A ) or  220  ( FIG. 2 ). In some examples, a computer-readable storage medium (e.g., memory  232 ) may store instructions, modules, or algorithms that, when executed, cause one or more processors (e.g., processor  231 ) to perform one or more of the illustrated steps in the flow chart. 
     The method of  FIG. 15B  includes receiving a data packet at the wireless source device, where the data packet comprises user input data with associated coordinate data ( 1502 ). The associated coordinate data may, for example, corresponds to a location of a mouse click event or a location of a touch event at a sink device. Source device  120  may then normalize the associated coordinate data to generate normalized coordinate data ( 1504 ). Source device  120  can normalize the coordinate data by scaling the associated coordinate data based on a ratio of the resolution of the display window and a resolution of the display of the source. Source device  120  can determine the resolution of the display of the source device and can receive the resolution of the display window from the wireless sink device. Source device may then process the data packet based o the normalized coordinate data ( 1506 ). The data packets described with reference to  FIGS. 15A and 15B  may generally take the form of the data packets described with reference to  FIG. 6  and may be used to control audio/video data at a source device. 
     For simplicity of explanation, aspects of this disclosure have been described separately with reference to  FIGS. 7-15 . It is contemplated, however, that these various aspects can be combined and used in conjunction with one another and not just separately. Generally, functionality and/or modules described herein may be implemented in either or both of the wireless source device and wireless sink device. In this way, user interface capabilities described in the current example may be used interchangeably between the wireless source device and wireless sink device. 
     The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, and integrated circuit (IC) or a set of ICs (i.e., a chip set). Any components, modules or units have been described provided to emphasize functional aspects and does not necessarily require realization by different hardware units. 
     Accordingly, the techniques described herein may be implemented in hardware, software, firmware, or any combination thereof. If implemented in hardware, any features described as modules, units or components may be implemented together in an integrated logic device or separately as discrete but interoperable logic devices. If implemented in software, the techniques may be realized at least in part by a computer-readable medium comprising instructions that, when executed in a processor, performs one or more of the methods described above. The computer-readable medium may comprise a tangible and non-transitory computer-readable storage medium and may form part of a computer program product, which may include packaging materials. The computer-readable storage medium may comprise random access memory (RAM) such as synchronous dynamic random access memory (SDRAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, magnetic or optical data storage media, and the like. The techniques additionally, or alternatively, may be realized at least in part by a computer-readable communication medium that carries or communicates code in the form of instructions or data structures and that can be accessed, read, and/or executed by a computer. 
     The code may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, an application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated software modules or hardware modules configured for encoding and decoding, or incorporated in a combined video codec. Also, the techniques could be fully implemented in one or more circuits or logic elements. 
     Various aspects of the disclosure have been described. These and other aspects are within the scope of the following claims.