Patent Publication Number: US-2023139203-A1

Title: Anti-Piracy Video Transmission and Display

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 15/714,575, filed Sep. 25, 2017, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Video content rights holders commonly use digital rights management software, secure devices, and other strategies to prevent unauthorized copying and distribution of video content. However, unauthorized copies of video content can still be made by using video recording devices to capture content being output by video displays. There remains an ever-present need for protecting the rights of content holders, and for countering the efforts of those would seek to make unauthorized copies of video content. 
     SUMMARY 
     The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosure. The summary is not an extensive overview of the disclosure. It is neither intended to identify key or critical elements of the disclosure nor to delineate the scope of the disclosure. The following summary merely presents some concepts of the disclosure in a simplified form as a prelude to the description below. 
     Some aspects of this disclosure relate to methods, systems and computing devices that prevent or interfere with video capture of content displayed on a video display, such as a television, monitor, projection screen, or other video display. Video capturing devices, such as camcorders, commonly have fairly low capture rates (e.g., 20 frames per second), whereas many video displays are capable of outputting content at much higher refresh rates (e.g., 120-240 frames per second). This refresh rate disparity can be used to display content that appears normal to a human viewer, but that is difficult or impossible to accurately capture with common video recording devices. 
     In one aspect, techniques described herein generate content for display that quickly cycles between different-colored frames at a rapid rate that may be imperceptible to human viewers. For example, a video display may output a first frame colored in shades of a first primary color (e.g., a frame with only red image data), followed by a second frame colored in shades of a second primary color (e.g., a frame with only green image data), followed by a third frame colored in shades of a third primary color (e.g., a frame with only blue image data). The human eye tends to blend sequential frames together if they are presented in quick succession, so that a human viewer will see a full color spectrum even though only a single color is displayed at any given time. The video display may repeatedly cycle between individual color frames, thus providing video content that appears normal to a human viewer. However, a camcorder or video recording device may capture only some of the color frames. Therefore, the video recorded by video recording devices may include undesirable color flicker or other color artifacts, which may deter unauthorized copying. 
     In some aspects, by displaying (and potentially transmitting) a reduced amount of color information for each frame, transmitted video content may omit certain color information for any given frame and thereby use a lower bandwidth on a transmission medium. The lower bandwidth on the transmission medium may beneficially enable more robust transmission properties that may be useful when signal loss becomes an issue. Therefore, techniques described herein may be useful to combat piracy and/or to lower the bandwidth of a transmitted video signal, among other benefits. 
     The methods, systems and computing devices described herein may be included as part of a network, such as a cable television distribution network. 
     The details of these and other embodiments of the present disclosure are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements and in which: 
         FIG.  1    illustrates an example network according to one or more aspects described herein. 
         FIG.  2    illustrates an example computing device on which the various elements described herein may be implemented according to one or more aspects described herein. 
         FIG.  3    illustrates an example process for causing content to be displayed according to a secure display mode. 
         FIG.  4    illustrates an example of selected video content and corresponding color-cycled content. 
         FIGS.  5 A,  5 B,  5 C,  5 D  are example transmission diagrams illustrating selected video content converted into transmitted video content and corresponding color-cycled content. 
         FIG.  6    illustrates an example of selected video content and corresponding color-cycled content. 
         FIGS.  7 A and  7 B  are example transmission diagrams illustrating selected video content converted into transmitted video content and corresponding color-cycled content. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of various illustrative embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown, by way of illustration, various embodiments in which aspects of the disclosure may be practiced. It is to be understood that other embodiments may be utilized, and structural and functional modifications may be made, without departing from the scope of the present disclosure. 
     A computing device with access to video content may implement techniques described herein to combat piracy by displaying video in repeating color cycles. The computing device may be part of a video distribution network, such as a cable television network, and/or may be connected to other sources of video content, such as the Internet, video players such as DVD and BLU-RAY players, and the like. Such computing systems may be part of a home entertainment system, a projection system (e.g., for a movie theater), or any other system for displaying video content. 
     The computing device may cause a display device to quickly display sequential frames of a video content, but to have each individual frame presented in just one color, such as a primary color, instead of as a full-color frame. In one embodiment, a cycle of frames may include a first frame of a first primary color (e.g., showing one frame of video content in red), a second frame of a second primary color (e.g., showing a next frame of video content in green), and a third frame of a third primary color (e.g., showing a next frame of video content in blue). The next cycle may similarly include three frames of three different primary colors. Various colors may be used as primary colors for a color cycle. For example, a color cycle may include a cyan frame, followed by a magenta frame, followed by a yellow frame. By quickly including individual colors in sequential frames, a human viewer&#39;s eyes may tend to blend the colors of the sequential frames, so the true full-color video content frame is still perceived over time, even though only components of a particular color are displayed in any one time. 
     In some embodiments, a color cycle may include a black-and-white or grayscale frame, which may beneficially increase the perceived brightness of the displayed video content. For example, a four-color cycle including a red frame, a green frame, a blue frame, and a white frame may appear brighter to a viewer than a three-color cycle including a red frame, a blue frame, and a green frame. In some embodiments, two primary colors may be used in some frames. For example, a two-color cycle may include a red-green frame, followed by a blue frame. As another example, a frame may be half one color (e.g., a top half of the frame may be red) and half another color (e.g., a bottom half of the frame may be green). In general, each frame of a color cycle may include reduced color information, and the plurality of frames forming a color cycle may collectively include a full color gamut. 
     In some embodiments, content may be modified before transmission over a local display link, such as a DISPLAYPORT link, HDMI link, DVI-D link, or some other link for transmitting video data. Such links may include multiple physical channels for transmitting different video color information simultaneously. For example, HDMI includes three physical transmission minimized differential signaling (TMDS) channels for transmitting three different primary colors according to a selected color space (e.g., one channel for red data, one channel for green data, and one channel for blue data when transmitting video in the RGB color space). Additionally or alternatively, content may be transmitted across other types of links. 
       FIG.  1    illustrates an example network  100  on which many of the various features described herein may be implemented. Network  100  may be any type of information distribution network, such as satellite, telephone, cellular, wireless, optical fiber network, coaxial cable network, and/or a hybrid fiber/coax (HFC) distribution network. Additionally, network  100  may be a combination of networks. Network  100  may use a series of interconnected communication links  101  (e.g., coaxial cables, optical fibers, wireless, etc.) and/or some other network (e.g., the Internet, a PSTN, etc.) to connect an end-point to a local office or headend  103 . Example end-points are illustrated in  FIG.  1    as premises  102  (e.g., businesses, homes, consumer dwellings, etc.) The local office  103  (e.g., a data processing and/or distribution facility) may transmit information signals onto the links  101 , and each premises  102  may have a receiver used to receive and process those signals. 
     There may be one link  101  originating from the local office  103 , and it may be split a number of times to distribute the signal to various homes  102  in the vicinity (which may be many miles) of the local office  103 . The links  101  may include components not illustrated, such as splitters, filters, amplifiers, etc. to help convey the signal clearly, but in general each split introduces a bit of signal degradation. Portions of the links  101  may also be implemented with fiber-optic cable, while other portions may be implemented with coaxial cable, other links, or wireless communication paths. 
     The local office  103  may include a termination system (TS)  104 , such as a cable modem termination system (CMTS) in a HFC network, a DSLAM in a DSL network, a cellular base station in a cellular network, or some other computing device configured to manage communications between devices on the network of links  101  and backend devices such as servers  105 - 107  (which may be physical servers and/or virtual servers, for example, in a cloud environment). The TS may be as specified in a standard, such as the Data Over Cable Service Interface Specification (DOCSIS) standard, published by Cable Television Laboratories, Inc. (a.k.a. CableLabs), or it may be a similar or modified device instead. The TS may be configured to place data on one or more downstream frequencies to be received by modems or other user devices at the various premises  102 , and to receive upstream communications from those modems on one or more upstream frequencies. The local office  103  may also include one or more network interfaces  108 , which can permit the local office  103  to communicate with various other external networks  109 . These networks  109  may include, for example, networks of Internet devices, telephone networks, cellular telephone networks, fiber optic networks, local wireless networks (e.g., WiMAX), satellite networks, and any other desired network, and the interface  108  may include the corresponding circuitry needed to communicate on the network  109 , and to other devices on the network such as a cellular telephone network and its corresponding cell phones. 
     As noted above, the local office  103  may include a variety of servers  105 - 107  that may be configured to perform various functions. The servers may be physical servers and/or virtual servers. For example, the local office  103  may include a push notification server  105 . The push notification server  105  may generate push notifications to deliver data and/or commands to the various homes  102  in the network (or more specifically, to the devices in the homes  102  that are configured to detect such notifications). The local office  103  may also include a content server  106 . The content server  106  may be one or more computing devices that are configured to provide content to users in the homes. This content may be, for example, video on demand movies, television programs, songs, text listings, etc. The content server  106  may include software to validate user identities and entitlements, locate and retrieve requested content, encrypt the content, and initiate delivery (e.g., streaming) of the content to the requesting user and/or device. 
     The local office  103  may also include one or more application servers  107 . An application server  107  may be a computing device configured to offer any desired service, and may run various languages and operating systems (e.g., servlets and JSP pages running on Tomcat/MySQL, OSX, BSD, Ubuntu, Redhat, HTMLS, JavaScript, AJAX and COMET). For example, an application server may be responsible for collecting television program listings information and generating a data download for electronic program guide listings. Another application server may be responsible for monitoring user viewing habits and collecting that information for use in selecting advertisements. Another application server may be responsible for formatting and inserting advertisements in a video stream being transmitted to the premises  102 . Another application server may be responsible for formatting and providing data for an interactive service being transmitted to the premises  102  (e.g., chat messaging service, etc.). 
     An example premises  102   a  may include an interface  120 . The interface  120  may comprise a modem  110 , which may include transmitters and receivers used to communicate on the links  101  and with the local office  103 . The modem  110  may be, for example, a coaxial cable modem (for coaxial cable links  101 ), a fiber interface node (for fiber optic links  101 ), or any other desired device offering similar functionality. The interface  120  may also comprise a gateway interface device  111  or gateway. The modem  110  may be connected to, or be a part of, the gateway interface device  111 . The gateway interface device  111  may be a computing device that communicates with the modem  110  to allow one or more other devices in the premises to communicate with the local office  103  and other devices beyond the local office. The gateway  111  may comprise a set-top box (STB), digital video recorder (DVR), computer server, or any other desired computing device. The gateway  111  may also include (not shown) local network interfaces to provide communication signals to devices in the premises, such as display devices  112  (e.g., televisions), additional STBs  113 , personal computers  114 , laptop computers  115 , wireless devices  116  (wireless laptops and netbooks, mobile phones, mobile televisions, personal digital assistants (PDA), etc.), a landline phone  117 , and any other desired devices. Examples of the local network interfaces include Multimedia Over Coax Alliance (MoCA) interfaces, Ethernet interfaces, universal serial bus (USB) interfaces, wireless interfaces (e.g., IEEE 802.11), BLUETOOTH® interfaces (including, for example, BLUETOOTH® LE), ZIGBEE®, and others. Premises  102   a  may further include one or more listening devices  119 , the operation of which will be further described below. 
       FIG.  2    illustrates an example computing device on which various elements described herein can be implemented. The computing device  200  may include one or more processors  201 , which may execute instructions of a computer program to perform any of the features described herein. The instructions may be stored in any type of computer-readable medium or memory, to configure the operation of the processor  201 . For example, instructions may be stored in a read-only memory (ROM)  202 , random access memory (RAM)  203 , removable media  204 , such as a Universal Serial Bus (USB) drive, compact disk (CD) or digital versatile disk (DVD), floppy disk drive, or any other desired electronic storage medium. Instructions may also be stored in an attached (or internal) hard drive  205 . The computing device  200  may include one or more output devices, such as a display  206  (or an external television), and may include one or more output device controllers  207 , such as a video controller. In some embodiments, the device controller  207  may implement an HDMI standard and/or a modified HDMI standard. There may also be one or more user input devices  208 , such as a remote control, keyboard, mouse, touch screen, microphone, etc. The computing device  200  may also include one or more network interfaces, such as input/output circuits  209  (such as a network card) to communicate with an external network  210 . The network interface may be a wired interface, wireless interface, or a combination of the two. In some embodiments, the interface  209  may include a modem (e.g., a cable modem), and network  210  may include the communication links and/or networks illustrated in  FIG.  1   , or any other desired network. 
     The  FIG.  2    example is an illustrative hardware configuration. Modifications may be made to add, remove, combine, divide, etc. components as desired. Additionally, the components illustrated may be implemented using basic computing devices and components, and the same components (e.g., processor  201 , storage  202 , user interface, etc.) may be used to implement any of the other computing devices and components described herein. 
       FIG.  3    illustrates a process that may be implemented by the computing device  200 , which may be a gateway  111 , set top box  113 , personal computer  114 , or some other device. The process may begin at step  301 , when the computing device  200  is turned on or otherwise begins operation of a mode for transmitting video content to a display device  206 . 
     At step  302 , a user and/or the computing device  200  may have selected video content. For example, the user may select a television program on a broadcast or on-demand channel, and/or a default or previously-selected video content may be displayed when the computing device  200  is turned on. Then, the computing device  200  may retrieve metadata that can be used to determine how the selected video content should be transmitted and displayed (e.g., using a color cycle technique) at the display device  206 . The video metadata may be electronic program guide (EPG) data and/or other metadata. The video metadata may be retrieved from storage, for example, one or more of ROM  203 , removable media  204 , or hard drive  205 . Additionally or alternatively, the video metadata may be received via a network, such as external network  210 . The video metadata received from an external network  210  may be EPG data received via a television distribution network and/or via the Internet. The video metadata may also be received from a local device, such as a video game console, tablet, or other device that may communicate with computing device  200  to provide video content to display  206 . Such received video metadata may be stored in the storage for later retrieval. Accordingly, at step  302 , the computing device  200  may receive video metadata from another device (e.g., in response to a request transmitted to the other device) and/or retrieve the video metadata from storage. 
     The video metadata may contain information about video content that may be transmitted to the display device  206 . The video content may include video channels (e.g., television channels), video sources (e.g., a connected device such as a video game console), or other video content assets (e.g., television episodes, movies, etc.). The video metadata may include descriptive information such as a title, genre, and summary of a particular video content asset, channel, or source. The video metadata may also include schedule information such as a time and channel of broadcast for a particular video content asset. 
     The video metadata may also include a security setting for each item of video content. For example, each television program on NBC may have its own security setting. The security setting may indicate that particular video content should or must be transmitted to and/or displayed by a display device  206  using a secure display mode. The security setting may be a binary setting specifying that a secure display mode is either required or not required for particular content, or it may be a setting that specifies one or more of a plurality of security settings. For example, the security setting may specify one or more parameters of a secure display mode, such as a set of allowed color cycles, a minimum display refresh rate, a maximum display refresh rate, and/or a range of allowed display refresh rates. Additionally or alternatively, the security setting may include an indication of whether the computing device  200  must transmit the video in a secure display mode, or whether the display device  206  may handle conversion to a secure display mode. In some cases, the security setting may reference a pre-defined set of parameters for a secure display mode. For example, a “high security” setting may map to a first set of parameters for a secure display mode, and a “medium security” setting may map to a second set of parameters (e.g., a more permissive set of parameters). 
     The video metadata may also include one or more time periods associated with a particular security setting, and may include multiple security settings for a given video content. Each of the multiple security settings may be associated with one or more time periods, or no time period. During a time period, the computing device  200  may enforce the associated security setting. Security settings with no associated time period may be enforced at any time. For example, a “high security” setting may be associated with a newly-released movie or television episode during the first 2 weeks of its initial air date, and a “medium security” setting may be associated with the same movie or episode during the following two weeks. Finally, a “low security” setting may be associated with the same movie for any other time. If no security settings are associated with video content, the computing device  200  may cause the video content to be displayed in a normal (e.g., non-secure) manner. 
     The video metadata may generated by and/or received from a device at the local office or headend  103 . For example, one of servers  105 ,  106 ,  107  may generate the video metadata, including the security setting(s) and/or associated time periods. The server may determine that a particular video content should be associated with a security setting(s) and/or associated time periods based on a type of video content and/or an indication from a rights owner associated with the video content. For example, the server may determine that a broadcast of a new episode of a hit show should be associated with a high security setting for the first two weeks after its first broadcast, and a medium security setting for the following two weeks. Accordingly, the server may generate video metadata including appropriate security settings and time periods and transmit the video metadata to computing device  200 . 
     At step  303 , the computing device  200  may determine one or more supported display modes, which may indicate supported display refresh rates (which may affect which color cycle modes, frame rates, or other security settings are compatible with the connected display). The computing device  200  may communicate with the display  206  (e.g., via an HDMI connection) to determine one or more display modes supported by display  206 . For example, the computing device  200  may receive extended display identification data (EDID) via a display data channel (DDC) of the HDMI channel. The EDID may contain information such as a maximum resolution supported by the display, a manufacturer and/or model of the display, what resolutions and corresponding refresh rates are supported by the display, and the like. In some embodiments, the EDID may further include information about specific secure display modes that are supported by the display (e.g., a “high security” mode, a “medium security” mode, and the like), and/or information about secure display mode parameters, such as supported color cycles, whether the display supports conversion into a secure display mode, and the like. Additionally or alternatively, information about supported secure display modes and/or supported parameters may be received via a Consumer Electronics Control (CEC) line, or via some other communication channel of the HDMI or other link. In cases where the display does not transmit certain information about the supported secure display modes and/or secure display mode parameters, such information may be retrieved from another device (e.g., from a remote server in communication with computing device  200 ) in response to a query identifying the display (e.g., by make and/or model, serial number, and/or some other identifier of the display). Additionally or alternatively, such secure display mode information may be retrieved from local storage of the computing device  200  (e.g., from a stored database comprising secure display mode information keyed to one or more display identifiers). Such secure display mode information, once received (e.g., from display device  206  and/or a remote server), may be stored by computing device  200  and reused in the future. 
     At step  304 , the computing device  200  may determine whether a selected video content (e.g., content asset, channel, and/or content source, etc.) is associated with a security setting. The selected video content asset may be broadcast video, on-demand video, recorded video, or any other video content. Computing device  200  may determine whether the video metadata contains one or more security settings associated with content for display at display  206 . Computing device  200  may further determine whether the one or more security settings are currently enforced (e.g., based on determining that the current time falls within a particular time period associated with a particular security setting). If multiple security settings are currently enforced for selected content, computing device  200  may determine which security setting takes precedence. For example, if a user selects a movie associated with a first security setting, and the movie is transmitting on a channel associated with a second security setting, the computing device  200  may select one of the first security setting or the second security setting. In some cases, the computing device  200  may determine that the more restrictive security setting (e.g., the security setting that permits fewer security modes) takes precedence. In some cases, the computing device  200  may select the most specific security setting (e.g., a security setting for a content asset over a security setting for a channel, or a security setting for a channel over a security setting for a content source). 
     Responsive to determining that the selected content is not secure content (e.g., based on determining that no security settings are associated with the selected content or that any security settings associated with the selected content are not currently enforced), at step  305  the computing device  200  may transmit the selected content to display  206  for display in a normal (e.g., non-secure) mode. If the computing device  200  receives a selection of new content at step  306  (e.g., because the user selects different content, the previously-selected content ends and new content begins, etc.), the computing device returns to step  304 . 
     At step  307 , responsive to determining that the selected content is secure content (e.g., based on determining at least one security setting is currently enforced), the computing device  200  may select a secure display mode to use for transmitting the content to display  206 . A secure display mode may specify multiple parameters for displayed content, including a color cycle (e.g., a three-color cycle of a red, green, and blue, a four-color cycle of red, green, blue, and white, etc.), a frame rate of the displayed content, and a transmission mode. Selection of the parameters of the secure display mode may depend on one or more factors including a frame rate of the selected video content, supported refresh rates of display  206 , security settings of the video metadata, and/or video conversion capabilities of the display  206 , as well as other factors.  FIGS.  4 ,  5 A- 5 D,  6 , and  7 A- 7 B  illustrate various combinations of secure display mode parameters, and the selection of such parameters based on various factors. 
     In some examples, the supported refresh rates of display  206  may be used to select a frame rate of transmitted or displayed content. The computing device  200  may receive a list of supported refresh rates, which may indicate a particular refresh rate (e.g., 240 Hz). The computing device may then determine a supported transmission or display frame rate for transmitted or displayed content by dividing a number of colors in a color cycle by the refresh rate (e.g., a 240 Hz refresh rate divided by 3 colors allows 80 frames per second of a first color, 80 frames per second of a second color, and 80 frames per second of a third color to be transmitted and/or displayed). This process may be repeated for each supported refresh rate of display  206 . The computing device  200  may thus determine which transmission rates and/or display rates are supported based on the list of supported refresh rates received from display  206 . 
     The computing device  200  may further determine at least some secure display mode parameters based on a maximum cycle duration, which may indicate the maximum time for completing a color cycle that will be invisible (or at least acceptable) to a human eye. Turning to  FIG.  4   , a maximum cycle duration  401  is illustrated with respect to selected video content  403  of a particular frame rate. The maximum cycle duration  401  may specify a maximum time during which the display  206  must cycle through all the colors of the color cycle while displaying in a secure display mode. For example, for a maximum cycle duration  401  of 60 ms, the display must display each frame of a three-color cycle for no more than 20 ms (e.g., a red frame for 20 ms, a green frame for 20 ms, and a blue frame for 20 ms), or each frame of a four-color cycle for no more than 15 ms (e.g., a red frame for 15 ms, a green frame for 15 ms, a blue frame for 15 ms, and a white frame for 15 ms). Exceeding the maximum cycle duration  401  may cause undesirable effects for viewers, such as excessive visible flickering of content. 
     The frame rate of the selected video content  403  may be compared to the maximum cycle duration  401  to determine which color cycles can be completed within the maximum cycle duration  401 . In the illustrated example of  FIG.  4   , selected video content  403  may have a relatively high frame rate in comparison to the maximum cycle duration  401 . As illustrated by  FIG.  4   , because at least four frames of selected video content fit within the maximum cycle duration  401 , selected video content  403  may be converted into, for example, color-cycled content using a three-color cycle ( 450 A) or a four-color cycle ( 405 B). 
     The selected video content  403  includes a sequence of frames for sequential display (with the first six frames illustrated).  FIG.  4    shows how each frame of selected video content  403 , which has full color information (e.g., red, green, and blue primary colors according to an RGB color gamut, although other color gamuts may be used), may be converted into a frame having only single color information according to a three-color cycle mode (as illustrated by color-cycled content  405 A) or a four-color cycle mode (as illustrated by color-cycled content  405 B). For example, according to a three-color cycle secure display mode ( 405 A), a first frame of the selected video content  403  may be converted to a first frame of color-cycled content  405 A having only the red component of the first frame of selected video content  403 . Such conversion of the selected video content  403  into color-cycled content  405  may be performed by the computing device  200  and/or by the display device  206 . 
       FIG.  5 A  illustrates transmission and display of content according to a first example secure display mode. In the illustrated secure display mode, selected video content  503  is converted to color-cycled content  505  using a four-color cycle. The selected video content  503  may be transmitted to the display device  206  using a standard transmission mode, and the display device  206  may convert the received video content to color-cycled content  505  for display. As illustrated, according to a normal transmission mode, three TMDS channels may be used to carry three color components (e.g., red, green and blue) of the original frame. For example, when frame  1  is transmitted during a first time period T1, TMDS Channel 0 may carry the red component information, TMDS Channel 1 may carry the green component information, and TMDS Channel 2 may carry the blue component information. The transmission proceeds similarly for a second frame, third frame, and so on. The display device  206 , which converts the received transmitted video content  504  to color-cycled content  505 , may simply discard unnecessary color information from transmitted video content  504 . For example, to convert the first frame data of transmitted video content  504  to a first frame of color-cycled content  505  (e.g., to generate red frame  1  of color-cycled content  505 ), the display device  206  may simply discard the other color data of transmitted video content  504  (e.g., the green and blue frame  1  data of transmitted video content  504 ). In some cases, the display device  206  may process the received transmitted video content  504  in order to generate one or more frames of the color-cycled content  505 . For example, the display device  206  may generate the illustrated white frame  4  of color-cycled content  505  by combining the red frame data, green frame data, and blue frame data of transmitted video content  504 , then converting the combined data to black-and-white data (e.g., grayscale data). So, while Frames  1 - 4  might not each be displayed in their original full color spectrum, if those 4 color-cycled sequential frames are displayed quickly enough, the human eye might not notice the difference, but a camcorder or smartphone camera might capture the individual colors in some or all of the frames. 
     In the above example, some of the frame data transmitted on the TMDS Channels are not actually used. For example, for Frame  1 , which is displayed in red in the color-cycled content  505 , the transmission of the blue and green components of Frame  1  might be unnecessary.  FIG.  5 B  illustrates transmission and display of video content according to a second example secure display mode, in which those unnecessary color frames are simply omitted from the TMDS Channels. In the illustrated second example secure display mode, the computing device  200  may avoid transmitting unnecessary data (e.g., data that would be discarded by the display device  206 ). For example, instead of transmitting green color data and blue color data for frame  1  of selected video content  503 , the computing device  200  may instead transmit blank data indicating that a frame has no green color data or blue color data. As another example, the computing device may transmit nothing at all on the transmission channels that would normally carry the green color data and blue color data. In some cases, the computing device  200  may transmit blank data in transmitted video content  506  in order to maintain compatibility with display devices  206  that do not support conversion of transmitted video content  506  into color-cycled content  505  at the display device  206 . However, in some cases (e.g., if the display device  206  supports such a setting), the computing device  200  may simply transmit nothing instead of blank data and/or may transmit other data during time periods that would otherwise contain blank data of transmitted video content  506 . In some cases, computing device  200  may process the selected video content  503  before transmission. For example, the illustrated frame  4  of selected video content  503  may be converted to grayscale by computing device  200  before separation into red, green, and blue components for transmitted video content  506 , in order to yield white (grayscale) frame  4  of color-cycled content  505 . 
     In the above example, which shows a four-color cycle, each TMDS Channel only transmits information about half of the time. A three-color cycle, which omits the white frame, might transmit information in the TMDS Channels only a third of the time. In alternative embodiments, this fact may allow the TMDS Channels to transmit at a slower data rate than normal.  FIG.  5 C  illustrates transmission and display of content according to a third example secure display mode in which a slower transmission frame rate is used. In the third example secure display mode, the frame rate of the transmitted video content  508  may be reduced in comparison to the frame rate of selected video content  503 . In the illustrated example, because only one third of the color data for each frame of selected video content  503  is being transmitted as transmitted video content  508  (e.g., because in the three-color cycle, data for the other two colors is being discarded for each frame), the frame rate may be reduced by a factor of three, and three frames may be transmitted on three transmission channels in a given time period (e.g., frames  1 - 3  may be transmitted during a first time period, and frames  4 - 6  may be transmitted during a second time period, as illustrated). Thus, for example, 90 frames-per-second content may be transmitted at 30 frames-per-second by transmitting three sequential frames for display as color-cycled content  507  during the same time period. 
     The  FIG.  5 C  example also shows three frames (e.g., red Frame  1 , green Frame  2 , and blue Frame  3 ) being transmitted on the TMDS Channel at the same time (e.g., time period T1). The display device  206  may receive these multiple frames of transmitted video content  508  at the same time, store some or all of them in a buffer, and cause them to be displayed sequentially as frames of color-cycled content  507  in order to present the video content in secure display mode. As illustrated by  FIG.  5 C  (with buffering and transmission delays not shown), a first frame of the selected video content  503  may correspond to a first frame of color-cycled content  507  displayed in a first color, a second frame of the selected video content  503  may correspond to a second frame of color-cycled content  507  displayed in a second color, and so on, with colors repeating in a three-color cycle in the illustrated example. 
     A secure display mode that uses a reduced transmission frame rate may beneficially provide more robust transmission characteristics, due to the lower data rate. Accordingly, such a reduced transmission frame rate mode may be beneficially useful with longer transmission cables, damaged transmission cables, or to address other causes of transmission signal degradation and/or signal loss, as further discussed for steps  311  and  312  of  FIG.  3   . 
     In the above example, the TMDS Channels were aligned, such that 3 frames were all received at the same time (T1), and the display device would buffer some of the frames until they were needed for display. In alternative embodiments, the frames may be staggered in the TMDS Channels to reduce the buffering requirement.  FIG.  5 D  illustrates transmission and display of content according to a fourth example secure display mode that staggers the frames. Similarly as for the third example secure display mode, in the fourth example secure display mode, the frame rate of transmitted video content  510  may be reduced in comparison to selected video content  503 . However, rather than transmitting multiple frames aligned in a single time period, the computing device  200  may transmit multiple frames in overlapping, staggered time periods. Such a transmission configuration may beneficially reduce buffering at the computing device  200  and/or at the display device  206 . 
     The display device  206  may receive the multiple frames transmitted at overlapping, staggered times and cause them to be displayed sequentially to present the video content in secure display mode. As illustrated by  FIG.  5 D  (with buffering and transmission delays not shown), a first frame of the selected video content  503  may correspond to a first frame of color-cycled content  507  of a first color, a second frame of the selected video content  503  may correspond to a second frame of color-cycled content  507  of a second color, and so on, with colors repeating in a three-color cycle in the illustrated example. 
       FIG.  6    illustrates another case of a maximum cycle duration  601  with respect to a selected video content  603  of a particular frame rate. In this case, the relatively low frame rate of the selected video content  603  in comparison to the maximum cycle duration  601  could cause excessive visible flickering for human viewers if the frame rate is not increased for color-cycled content. The maximum cycle duration  601  thus provides a frame rate criterion (e.g., a minimum frame rate). If the frame rate criterion is not satisfied (e.g., the video content  603  has a frame rate below a minimum frame rate), the computing device  200  may select an increased frame rate security mode. In other words, compared to the selected video content  403  of  FIG.  4   , the selected video content  603  of  FIG.  6    may comprise fewer frames per second, such that cycling colors by causing a first frame of selected video content  603  to be displayed in a first color, a second frame of selected video content  603  to be displayed in a second color, and so on, may cause the maximum cycle duration  601  to be exceeded, which may cause undesirable effects for viewers, such as visible flickering of content. 
     In order to convert such selected video content  603  to a secure display mode, a first frame of the selected video content  603  may be converted into multiple frames of color-cycled content  605 , thereby increasing the frame rate of the color-cycled content. For example, a frame  1  of selected video content  603 , which may have three color components, may be converted three sequential frames of color-cycled content  605 A, each having a different color. As another example, frame  1  of selected video content  603  may be converted into four frames of color-cycled content  605 B, each having a different color. Accordingly, the color-cycled content  605  may be increased in frame rate in comparison to the selected video content  603 . Such conversion may be performed by the computing device  200  and/or by the display device  206 . 
       FIG.  7 A  illustrates transmission and display of content according to a fifth example secure display mode that generates the increased frame rate color-cycled content  705  at the display device  206 . In the fifth example secure display mode, the computing device  200  may transmit the selected video content  703  to the display  206  as transmitted video content  704  according to a normal transmission mode (e.g., at a same frame rate as the selected video content). For example, first color data, second color data, and third color data for a first frame of selected video content  703  may be transmitted together on three corresponding transmission channels as transmitted video content  704 . Then, the display device  206  may sequentially display the first color data as a first frame of color-cycled content  705 , followed by the second color data as a second frame of color-cycled content  705 , followed by the third color data as a third frame of color-cycled content  705 , and so on. In some modes, the display device may generate additional color-cycled content  705  frames based on the color data. For example, the display device  206  may generate a fourth color-cycled content frame in grayscale using the received first, second, and third color data (e.g., to generate a four-color cycle color-cycled content, such as color-cycled content  605 B of  FIG.  6   ). 
     In some cases (e.g., when a display device  206  lacks the capability of generating the increased frame rate color cycle content  705 ), the computing device  200  may increase a frame rate of transmitted video content  706 . The computing device  200  may optionally transmit blank data (e.g., during time periods when a TMDS channel does not need to carry color information for display).  FIG.  7 B  illustrates transmission and display of content according to a sixth example secure display mode. In the sixth example secure display mode, the computing device  200  may increase a frame rate of the transmitted video content  706  as compared to the selected video content  703 . For example, selected video content  703  at 30 frames per second may be transmitted as transmitted video content  706  at 90 frames per second, with each frame of selected video content  703  split into three frames of transmitted video content  706  in different colors. In another example (not illustrated), selected video content  703  at 30 frames per second may be transmitted as transmitted video content at 120 frames per second, with each frame of selected video content  703  split into four transmitted frames in different colors. As illustrated, transmitted video content  706  may include a frame for display on only a single transmission channel of multiple transmission channels at a time, and the other transmission channels may contain blank data, no data at all, or other data. For example, during time period T1, TMDS Channel 0 may carry red color information for frame  1  of transmitted video content  706 , and second and third transmission channels may carry blank data (as illustrated), no data at all, or other data. The computing device  200  may transmit blank data in order to maintain compatibility with display devices  206  that do not support conversion of content at the display device  206  (e.g., for a legacy display device  206  that implements standard HDMI transmissions). In some embodiments, each transmitted video content  706  frame at the higher frame rate may be transmitted with additional error correction information as compared to a normal transmission (e.g., one or more additional error correction bits per byte as compared to an HDMI normal transmission). In some cases, computing device  200  may process the selected video content  703  before transmission. For example, a grayscale frame may be generated by computing device  200 , then separated into red, green, and blue components for transmission. 
     Turning back to  FIG.  3   , at step  308 , after selecting a secure display mode, the computing device  200  may convert the selected video content before transmission to the display device  206  in accordance with the selected secure display mode. According to some secure display modes, the computing device  200  may transmit the selected video content using conventional transmission methods (e.g., using standard HDMI transmissions), and the display device  206  may convert the transmitted content into color-cycled content. According to some secure display modes, the computing device  200  may replace certain color data of the selected video content with blank color data, replace certain color data with other data, and/or transmit nothing instead of transmitting certain color data. According to some secure display modes, the computing device  200  may lower the frame rate of the transmitted video content in comparison to the selected video content. According to some secure display modes, the computing device  200  may transmit multiple color-cycled content frames simultaneously and/or in overlapping time periods. According to some secure display modes, the computing device  200  may increase a frame rate of the transmitted video content in comparison to the selected video content. 
     At step  309 , the computing device  200  may transmit the converted video content to the display device  206 . The video content may be transmitted across a local video connection, such as an HDMI connection. Accordingly, the various color data may be separated and transmitted across different transmission channels of the link. For example, as illustrated in  FIGS.  5 A- 5 D,  7 A, and  7 B , one transmission channel may be used to carry red data, one transmission channel may be used to carry green data, and one transmission channel may be used to carry blue data. However, other colors (e.g., cyan, yellow, and magenta) or color spaces (e.g., a YCC color space including one luma channel and two chroma channels) may be used for transmission. 
     At step  310 , if the computing device  200  receives a selection of new content (e.g., because the user selects different content, the previously-selected content ends and new content begins, etc.), the computing device returns to step  304 . Otherwise, the computing device  200  may continue transmitting the selected video content. 
     In some cases, in response to detecting a transmission error at step  311 , the computing device  200  may adjust the selected secure display mode to reduce a bandwidth of the transmission at step  312 . The computing device  200  may receive an indication from the display device  206  that the display device  206  did not receive one or more frames, detected one or more errors, or otherwise received a degraded signal. Responsive to receiving the indication, at step  312 , the computing device  200  may adjust one or more parameters of the secure display mode to lower a bandwidth of the transmission. For example, the computing device  200  may reduce a frame rate of the transmitted video content (e.g., as in  FIG.  5 C or  5 D ), or switch from a four-color cycle to a three-color cycle. The lower bandwidth transmission may be more robust to signal degradation. 
     One or more aspects of the disclosure may be embodied in computer-usable data and/or computer-executable instructions, such as in one or more program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other data processing device. The computer executable instructions may be stored on one or more computer readable media such as a hard disk, optical disk, removable storage media, solid state memory, RAM, etc. The functionality of the program modules may be combined or distributed as desired in various embodiments. In addition, the functionality may be embodied in whole or in part in firmware or hardware equivalents such as integrated circuits, field programmable gate arrays (FPGA), application-specific integrated circuits (ASIC), and the like. Particular data structures may be used to more effectively implement one or more aspects of the invention, and such data structures are contemplated within the scope of computer executable instructions and computer-usable data described herein. 
     Aspects of the disclosure have been described in terms of illustrative embodiments thereof. While illustrative systems and methods as described herein embodying various aspects of the present disclosure are shown, it will be understood by those skilled in the art, that the disclosure is not limited to these embodiments. Modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. For example, each of the features of the aforementioned illustrative examples may be utilized alone or in combination or sub-combination with elements of the other examples. For example, any of the above described systems and methods or parts thereof may be combined with the other methods and systems or parts thereof described above. For example, the steps illustrated in the illustrative figures may be performed in other than the recited order, and one or more steps illustrated may be optional in accordance with aspects of the disclosure. It will also be appreciated and understood that modifications may be made without departing from the true spirit and scope of the present disclosure. The description is thus to be regarded as illustrative instead of restrictive on the present disclosure.