# Patent

## Title
Content streaming with client device trick play index

## Abstract

An apparatus downloads files of encoded video including interspersed key frames over a communication network. The apparatus plays back video from the downloaded files and creates a trick play index based on the downloaded files. The trick play index indicates network locations of the key frames in the encoded video files. When the apparatus receives a trick play request, such as rewind or fast forward, the client device downloads the key frames from the indicated network locations, and plays back video from the downloaded key frames.

## Background
BACKGROUND
Distribution of multimedia video (also referred to herein as “media” and/or “program(s)”), such as movies and the like, from network services to a client device, may be achieved through adaptive bitrate streaming of the video. Prior to streaming, the video may be encoded at different bitrates and resolutions into multiple bitrate streams that are stored in the network services. Typically, each of the bitstreams includes time-ordered segments of encoded video.
Adaptive bitrate streaming includes determining an available streaming bandwidth at the client device, and then downloading a selected one of the different bitrate streams from the network services to the client device based on the determined available bandwidth. While streaming, the client device downloads and buffers the successive encoded video segments associated with the selected bitstream. The client device decodes the buffered encoded video segments to recover the video therein, and then plays back the recovered video on the client device, e.g., in audio-visual form.
In normal playback, the client device plays back the video recovered from each of the buffered segments in the order in which the video was originally encoded, i.e., in a forward direction. The client device may offer playback modes or features in addition to normal playback. Such additional playback features may include rewind, fast forward, skip, and so on, as is known. The additional playback features are referred to herein as trick play features.
In order to implement trick play features, such as rewind, the client device requires access to video that has already been played. Therefore, the client device may be required to store large amounts of already downloaded and played video in order to meet the demands of a selected trick play feature. However, many client devices, especially small, hand-held devices, have limited memory capacity and, therefore, may be unable to store the requisite amount of video.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an example network environment in which embodiments directed to streaming of multimedia content, such as video programs, with trick play features may be implemented.
FIG. 2 is an illustration of an example encoded multimedia video program generated by and stored in network services of FIG. 1.
FIG. 3 is an illustration of an example frame structure of an encoded video block of FIG. 2.
FIG. 4A is a sequence diagram of example high-level interactions between network services and a client device used to initiate streaming, implement normal streaming and playback, and implement trick play features in streaming embodiments.
FIG. 4B is a sequence diagram corresponding to an embodiment in which a trick play index is stored in network services instead of a client device.
FIG. 5 is an example Profile message used in streaming.
FIG. 6 is an example Playlist message used in streaming.
FIG. 7 is an illustration of an example trick play index created and used by a client device to implement trick play features.
FIG. 8 is a flowchart of an example method of streaming multimedia content with trick play features.
FIG. 9 is a flowchart of an example method of creating a trick play index.
FIG. 10 is a block diagram of an example computer system.
FIG. 11 is a block diagram of an example computer system corresponding to any of the network servers in the environment of FIG. 1.
FIG. 12 is a block diagram of an example system representing a client device of FIG. 1.



In the drawings, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears.
DETAILED DESCRIPTION









TABLE OF CONTENTS







1
Network Environment . . .
 - 5 -


2
Container Files−Streaming Sources . . .
 - 9 -


2.1
Encoded Video Frame Structure . . .
- 12 -


3
Sequence Diagrams . . .
- 14 -


3.1
Start-up . . .
- 14 -


3.2
Normal Streaming and Playback . . .
- 15 -


3.3
Trick Play . . .
- 17 -


3.4
Trick Play Index Stored Offsite . . .
- 19 -


4
Profile and Playlist Messages . . .
- 20 -


4.1
Profile Message . . .
- 20 -


4.2
Playlist Message . . .
- 21 -


5
Trick Play Index . . .
- 22 -


6
Method Flowcharts . . .
- 22 -


6.1
Trick Play with Trick Play Index . . .
- 22 -


6.2
Creating a Trick Play Index . . .
- 24 -


7
Systems . . .
- 25 -









1 Network Environment

FIG. 1 is a block diagram of an example network environment 100 in which a client device 104 creates and uses a memory efficient trick play index to implement trick play features, such as rewind and fast forward, while the client device streams/downloads multimedia video files from network services 102 for playback. As will be described in detail below, client device 104 creates the trick play index based on the downloaded video files. The trick play index supports trick play features in a manner that obviates the need for client device 104 to store large amounts of already downloaded video. To that end, the trick play index identifies a minimal subset of video content, referred to as key frames, interspersed in, and representative of, the full video content being streamed. In response to a trick play request, the client device downloads the key frames from their corresponding locations as indicated in the trick play index, and plays back the content therein to implement the requested trick play feature.
Environment 100 supports trick play features in different adaptive bitrate streaming embodiments, including on-demand streaming, live streaming, and real-time streaming embodiments. On-demand streaming includes encoding the content of a program from start to end in its entirety and then, after the entire program has been encoded, streaming, i.e., downloading, the encoded program to a client device. An example of on-demand streaming includes streaming a movie from a Video-on-Demand (VOD) service to a client device.
Live streaming includes encoding successive blocks of live content, i.e., a live program, as they are received from a content source, and then streaming each encoded block as it becomes available for download. Live streaming may include streaming live scenes, i.e., video, captured with a video camera.
Real-time streaming is similar in most aspects to live streaming, except that the input to real-time streaming is not a live video feed. Rather, the input, or source, may include successive encoded blocks, or input blocks, that have a format not suitable for streaming (e.g., for a given system) and must, therefore, be decoded and re-encoded (i.e., transcoded) into an encoded format that is suitable for streaming (in the given system). Real-time streaming handles the successive incompatible input blocks similar to the way live streaming handles the successive blocks of live content.
Network environment 100 is now described in detail. Network environment 100 includes server-side or network services 102 (also referred to simply as “services 102”) and client-side device 104. Network services 102 may be implemented as Internet cloud-based services. Network services 102 interact and cooperate with each other, and with client device 104, to manage and distribute, e.g., stream, multimedia content from content sources 108 to the client devices, over one or more communication network 106, such as the Internet. Network services 102 communicate with each other and with client devices 104 using any suitable communication protocol, such as an Internet protocol, which may include Transmission Control Protocol/Internet Protocol (TCP/IP), Hypertext Transfer Protocol (HTTP), etc., and other non-limiting protocols described herein.
Content sources 108 may include any number of multimedia content sources or providers that originate live and/or pre-recorded multimedia content (also referred to herein simply as “content”), and provide the content to services 102, directly, or indirectly through communication network 106. Content sources 108, such as Netflix®, HBO®, cable and television networks, and so on, may provide their content in the form of programs, including, but not limited to, entertainment programs (e.g., television shows, movies, cartoons, news programs, etc.), educational programs (e.g., classroom video, adult education video, learning programs, etc.), and advertising programs (e.g., commercials, infomercials, or marketing content). Content sources 108, such as, e.g., video cameras, may capture live scenes provide the resulting real-time video to services 102. Content sources may also include live broadcast feeds deployed using protocols such as Real-time Transport Protocol (RTP), and Real-time Messaging Protocol (RTMP).
Network services 102 include, but are not limited to: an encoder 110 to encode content from content sources 108; a content delivery network (CDN) 112 (also referred to as a “download server 112”) to store the encoded content, and from which the stored, encoded content may be streamed or downloaded to client device 104; and a real-time service (RTS) 114 (also referred to as a “real-time server (RTS) 114”) to (i) control services 102, and (ii) implement an RTS streaming control interface through which client device 104 may initiate and then monitor both on-demand, live, and real-time streaming sessions. Each of services 102 may be implemented as one or more distinct computer servers that execute one or more associated server-side computer program applications suited to the given service.
Encoder 110 may be implemented as a cloud encoder accessible over communication network 106. Encoder 110 encodes content provided thereto into a number of alternative bitstreams 120 (also referred to as encoded content) to support adaptive bitrate streaming of the content. For increased efficiency, encoder 110 may be implemented as a parallel encoder that includes multiple parallel encoders. In such an embodiment, encoder 110 divides the content into successive blocks or clips each of a limited duration in time. Each block may include a number of successive picture frames, referred to collectively as a group of pictures (GOPs). Encoder 110 encodes the divided blocks or GOPs in parallel to produce alternative bitstreams 120. Encoder 110 may also include transcoders to transcode input files from one encoded format to another, as necessary.
Alternative bitstreams 120 encode the same content in accordance with different encoding parameters/settings, such as at different encoding bitrates, resolutions, frame rates, and so on. In an embodiment, each of bitstreams 120 comprises a large number of sequential (i.e., time-ordered) files of encoded content, referred to herein as container files (CFs), as will be described further in connection with FIG. 2.
After encoder 110 has finished encoding content, e.g., after each of the content blocks is encoded, the encoder uploads the encoded content to CDN 112 for storage therein. CDN 112 includes one or more download servers (DSs) to store the uploaded container files at corresponding network addresses, so as to be accessible to client device 104 over communication network 106.
RTS 114 acts as a contact/control point in network services 102 for client device 104, through which the client device may initiate and then monitor its respective on-demand, live, and real-time streaming sessions. To this end, RTS 114 collects information from services 102 that client device 104 may use to manage its respective streaming sessions, and provides the collected information to the client device via messages (described below) when appropriate during streaming sessions, thus enabling the client device to manage its streaming sessions. The information collected by RTS 114 (and provided to client device 104) identifies the encoded content, e.g., the container files, stored in CDN 112, and may include, but is not limited to, network addresses of the container files stored in the CDN, encoding parameters use to encode the container files, such as their encoding bitrates, resolutions, and frame rates, and file information, such as file sizes, and file types.
Client device 104 may be capable of wireless and/or wired communication with network services 102 over communication network 106, and includes processing, storage, communication, and user interface capabilities sufficient to provide all of the client device functionality described herein. Such functionality may be provided, at least in part, by one or more client applications 107, such as computer programs, that execute on client device 104. Client applications 107 may include:

    
    
        a. a Graphical User Interface (GUI) through which a user of the client device may interact with and request services from corresponding server-side applications hosted in services 102. The GUI may also present trick play feature selections to the user, such as rewind and fast forward. Under user control through the GUI, client device 104 may request/select (i) programs to be streamed from services 102, and (ii) trick play features to control playback of the streamed programs;
        b. streaming and playback applications to stream/download the selected programs from the services, and playback, i.e., present, the streamed programs on client device 104, under user control, through the GUI; and
        c. a trick play application integrated with the GUI, and the streaming and playback applications, to create the trick play index (TPI) (indicated as box “TPI” in FIG. 1) and use it to implement the trick play features as described herein.
    
    


The trick play index TPI created by client device 104 may be stored in the client device, as indicated in FIG. 1. Alternatively, client device 104 may transmit the trick play index to an offsite location for storage at that location. For example, the trick play index may be stored at a specified network address in an Internet cloud service, or at some other physical location separated from client device 104. In such an embodiment, after the trick play index has been stored at the offsite location, client device 104 must access/download the trick play index from the offsite location before using the trick play index to implement trick play features, as described below.
2 Container Files—Streaming Sources
As described above, encoder 110 encodes multimedia content from content sources 108, and CDN 112 stores the encoded content. To support adaptive bitrate streaming, encoder 110 encodes the content at multiple encoding levels, where each level represents a distinct combination of an encoding bitrate and a video resolution (for video content), to produce multiple streams for the content. The multiple streams are indexed according to their respective encoding levels. While streaming the encoded program from CDN 112, client device 104 may switch between streams, i.e., levels (and thus encoded bitrates and resolutions) according to conditions at the client device.
FIG. 2 is an illustration of an example encoded multimedia video program 200 generated by encoder 110 and stored in CDN 112. Encoded video program 200 includes two encoded video streams 1, 2 encoded at corresponding encoding levels (“Video ID” in FIG. 2) L1, L2. Each of encoding levels L1, L2 corresponds to a distinct combination of an encoding bitrate (Rate) and a video resolution (Res). In the example, encoding levels L1, L2 corresponds to Rate1/Res1, Rate2/Res2, respectively. Although the example of FIG. 2 includes only two encoding levels, in practice, an encoded video program typically includes many more than two levels of encoding, such as 8 to 15 levels of encoding.
Each of streams 1, 2 includes a distinct, time-ordered, sequence of container files CF (i.e., successive container files CF), where time is depicted in FIG. 2 as increasing in a downward vertical direction. The successive container files CF, of each of streams 1, 2, each includes (i.e., encodes) a block or segment of video (also referred to herein as an encoded video block or segment), so that the successive container files of each of the streams encode successive contiguous encoded video blocks. Each container file CF includes a time code TC to indicate a duration of the video encoded in the block of the container file, and/or a position of the container file in the succession of container files comprising the corresponding stream. The time code TC may include a start time and end time for the corresponding encoded video block. In an example in which each container file CF encodes two seconds of video, time codes TC1, TC2, and TC3 may represents start and end times of 0 s (seconds) and 2 s, 2 s and 4 s, and 4 s and 6 s, respectively, and so down the chain of remaining successive container files.
The encoded blocks of the container files CF in a given stream may encode the same content (e.g., video content) as corresponding blocks in the other streams. For example, the stream 1 block corresponding to time code TC1 has encoded therein the same video as that in the stream 2 block corresponding to TC1. Such corresponding blocks encode the same content and share the same time code TC, i.e., they are aligned or coincide in time.
In an embodiment, a program stream index 204 may be associated with encoded video program 200 to identify each of the streams therein (e.g., streams 1, 2). RTS 114 may create (and store) program stream index 204 based on the information collected from encoder 110 and CDN 112, as described above in connection with FIG. 1. Then, during a live streaming session, for example, RTS 114 may provide information from program stream index 204 to client device 104 so as to identify appropriate container file addresses to the client device.
Program stream index 204 includes (i) address pointers (e.g., network addresses, such as Uniform Resource Locators (URLs)) 210-1, 210-2 to corresponding streams 1, 2, and (ii) encoder parameters/settings associated with the encoded streams including, but not limited to, encoding levels L1, L2 (including the encoding bitrates and resolutions Rate1/Res1 and Rate2/Res2), frame rates, encoding techniques/standards, and file types and sizes of the container files CF. Address pointers 210-1, 210-2 may point to respective lists of addresses A1, A2 of the container files CF comprising each of streams 1, 2. Address lists A1, A2 may each be represented as an array or linked list of container file network addresses, e.g., URLs. Accordingly, access to the information in program stream index 204 results in possible access to all of the container files associated with streams 1, 2.
Although each of container files CF depicted in FIG. 2 represents a relatively small and simple container structure, larger and more complicated container structures are possible. For example, each container file may be expanded to include multiple clusters of encoded media, each cluster including multiple blocks of encoded media, to thereby form a larger container file also suitable for embodiments described herein. The larger container files encode an equivalent amount of content as a collection of many smaller container files.
Container files may encode a single stream, such as a video stream (as depicted in FIG. 2), an audio stream, or a text stream (e.g., subtitles). Alternatively, each container file may encode multiple multiplexed streams, such as a mix of video, audio, and text streams. In addition, a container file may encode only a metadata stream at a relatively low bitrate.
In embodiments: the container files may be Matroska (MKV) containers based on Extensible Binary Meta Language (EBML), which is a derivative of Extensible Binary Meta Language (XML), or files encoded in accordance with the Moving Picture Experts Group (MPEG) standard; the program index may be provided in a Synchronized Multimedia Integration Language (SMIL) format; and client device 104 may download container files from CDN 114 over networks 106 using the HTTP protocol. In other embodiments, the container file formats may include OGG, flash video (FLV), Windows Media Video (WMV), or any other format.
Exemplary, non-limiting, encoding bitrates for different levels, e.g., levels L1, L2, may range from below 125 kilo-bits-per-second (kbps) up to 15,000 kbps, or even higher, depending on the type of encoded media (i.e., content). Video resolutions Res 1-Res 4 may be equal to or different from each other.
The container files may support adaptive streaming of encoded video programs across an available spectrum bandwidth that is divided into multiple, i.e., n, levels. Video having a predetermined video resolution for each level may be encoded at a bitrate corresponding to the bandwidth associated with the given level. For example, in DivX® Plus Streaming, by Rovi Corporation, the starting bandwidth is 125 kbps and the ending bandwidth is 8400 kbps, and the number n of bandwidth levels is eleven (11). Each bandwidth level encodes a corresponding video stream, where the maximum encoded bitrate of the video stream (according to a hypothetical reference decoder model of the video coding standard H.264) is set equal to the bandwidth/bitrate of the given level. In DivX® Plus Streaming, the 11 levels are encoded according to 4 different video resolution levels, in the following way: mobile (2 levels), standard definition (4 levels), 720p (2 levels), and 1080p (3 levels).
2.1 Encoded Video Frame Structure
FIG. 3 is an illustration of an example frame structure 300 of an encoded video block of FIG. 2. Video encoding includes capturing a number of successive picture frames, i.e., a GOP, at a predetermined video frame rate, and encoding each of the captured frames, in accordance with an encoding standard/technique, into a corresponding encoded video frame. Exemplary encoding standards include, but are not limited to, block encoding standards, such as H.264 and Moving Picture Experts Group (MPEG) standards. Collectively, the encoded video frames form an encoded video block, such as an encoded video block in one of container files CF. The process repeats to produce contiguous encoded video blocks.
The encoding process may encode a video frame independent of, i.e., without reference to, any other video frames, to produce an encoded video frame referred to herein as a key frame. For example, the video frame may be intra-encoded, or intra-predicted. Such key frames are referred to as I-Frames in the H.264/MPEG standard set. Since the key frame was encoded independent of other encoded video frames, it may be decoded to recover the original video content therein independent of, i.e., without reference to, any other encoded video frames. In the context of streaming, the key frame may be downloaded from CDN 112 to client device 104, decoded independent of other encoded frames, and the recovered (decoded) video played back, i.e., presented, on the client device.
Alternatively, the encoding process may encode a video frame based on, or with reference to, other video frames, to produce an encoded video frame referred to herein as a non-key frame. For example, the video frame may be inter-encoded, i.e., inter-predicted, to produce the non-key frame. Such non-key frames include P-Frames and B-frames in the H.264/MPEG standard set. The non-key frame is decoded based on one or more other encoded video frames, e.g., key-frames, reference frames, etc. In the context of streaming, the non-key frame may be downloaded from CDN 112 to client device 104, decoded based on other encoded frames, and the recovered video played back.
With reference again to FIG. 3, frame structure 300 of the encoded video block includes, in a time-ordered sequence, a first set of successive non-key frames 304, a key frame 306, and a second set of successive non-key frames 308. Accordingly, key frame 306 is interspersed among the encoded video frames of the encoded video block. The position of key frame 306 relative to the non-key frames in block 300 may vary, e.g., the position may be at the top, the middle, the bottom, or elsewhere in the block. Moreover, multiple key frames may be interspersed among the encoded video frames of the encoded video block, and separated from each other by multiple non-key frames.
A key/non-key (K/NK) flag associated with each of the frames 304, 306, and 308 indicates whether the associated frame is a key-frame or a non-key frame. Each of the key and the non-key frames may include a predetermined number of bytes of encoded video.
In an example in which the encoded video block represented by frame structure 300 encodes 2 seconds of video captured at a video frame rate of 30 frames per second (fps), the frame structure includes 60 encoded video frames, which may include N (i.e., one or more) interspersed key frames, and 60-N non-key frames. Typically, the number of non-key frames exceeds the number of key frames.
3 Sequence Diagrams
FIG. 4A is a sequence diagram of example high-level interactions 400 between network services 102 and client device 104 used to initiate, i.e., start-up, streaming, implement normal streaming and playback, and implement trick play features in on-demand, live, and real-time streaming embodiments. Interactions 400 progress in time from top-to-bottom in FIG. 4A, and are now described in that order.
3.1 Start-Up
At 410, a user of client device 104 selects content, such as a video program, to be streamed using the client device GUI.
At 422, client device 104 sends a “Start” message (also referred to as a “begin playback” message) to RTS 114 to start a streaming session. The Start message includes an identifier (ID) of the content to be streamed and a current time stamp. The ID identifies content from a content source that is to be streamed to client 104, and may indicate, e.g., a channel, program name, and/or source originating the content to be streamed. The current time stamp (also referred to as “current time”) indicates a current time, such as a Universal Time Code (UTC). The UTC may be acquired from any available UTC time service, as would be appreciated by those or ordinary skill in the relevant arts.
It is assumed that at the time the Start message is issued, the content identified therein has already been encoded and is available for streaming, e.g., for video-on-demand streaming, or will begin to be encoded shortly after the time of the Start message, e.g., for live and real-time streaming. It is also assumed that RTS 114 has collected, or will be collecting, the information related to the encoded program from encoder 110 or CDN 115, such as a program stream index, e.g., program index 204, sufficient to identify the identified content in network services 102.
At 424, in response to the Start message, RTS 114 sends an encoding profile message (referred to as a “Profile” message) to client 104. The Profile message lists different encoding profiles used to encode the identified content, e.g., as available from the program stream index for the identified content. Each of the profiles specifies encoding parameters/settings, including, but not limited to: content type (e.g., audio, video, or subtitle); an encoding level corresponding to an encoding bitrate and resolution (e.g., levels L1 and L2); and a container file type, e.g., a Multipurpose Internet Mail Extensions (MIME) type.
In response to the Profile message, client device 104 selects an appropriate encoding level (e.g., an appropriate combination of an encoding bitrate and a resolution) among the levels indicated in the Profile message for streaming the identified content. Client device 104 may determine the appropriate encoding level based on a communication bandwidth at the client device.
3.2 Normal Streaming and Playback
After startup, normal streaming and playback begins, as follows.
At 432, after client device 104 has selected the encoding level, the client device sends a GetPlaylist message to RTS 114 to request a list of any new container files that have been uploaded since the client device last downloaded container files (if any) from CDN 112. The GetPlaylist message includes selection criteria for uploaded container files, namely, a current time and the selected encoding level. The current time represents a time code associated with the last container file downloaded by client device 104 (if any) in the current streaming session.
In response to the GetPlaylist message, RTS 114:

    
    
        a. selects the uploaded container files, as identified to the RTS that meet the criteria specified in the GetPlaylist message. The selected, uploaded container files are those container files that have (i) a time code greater than the current time, and (ii) an encoding level that matches the level specified in the GetPlaylist message from the client device;
        b. generates a Playlist message identifying the selected container files; and
        c. at 433, sends the Playlist message to client device 104.
    
    


For each of the selected container files, the Playlist message includes the following information: the type of content encoded in the container file (e.g., video, audio, or subtitle); an address (e.g., URL) of the container file in CDN 112 (e.g., a subset of the addresses A1 or A2); a time code, e.g., a start time and an end time, associated with the content block encoded in the container file; and a file size of the container file.
At 434, in response to the Playlist message, client device 104 downloads container files from addresses in CDN 112 based on, i.e., as identified in, the Playlist message.
At 436, client device 104 decodes all of the key frames and the non-key frames of the encoded content block from each of the downloaded container files to recover the original content therein, and then presents the recovered content, whether in audio, visual, or in other form, on client device 104. The process of decoding the encoded content from the key and non-key frames and then presenting the recovered content on client device 104 is referred to as “normal playback” on the client device. In normal playback, the content recovered from successive downloaded container files is played back on client device 104 in a forward (play) direction, i.e., in an order of increasing time code. For example, with reference again to FIG. 2, the content is played back from container files CF in the time code order of 0 s-2 s, 2 s-4 s, 4 s-6 s, and so on. For normal playback, the decoded video frames are presented at a frame rate equal to the frame rate at which the video was original captured and encoded, e.g., at a rate of 30 fps.
The normal streaming and playback sequence repeats. Therefore, in summary, in the streaming and playback sequence, client device 104 periodically requests and downloads Playlist messages, downloads container files indicated in the Playlist messages, and plays back the content from the downloaded container files in the forward direction.
3.3 Trick Play
At any time during the normal streaming and playback sequence, the user may select a trick play feature through the GUI. Trick play features include, but are not limited to, rewind and fast forward, in which client device 104 rewinds and fast forwards through previously played back content. Once the user has selected the trick play feature, client device 104 uses a trick play index, e.g., TPI 107a, to implement the trick play feature in a memory efficient manner, as will be described below.
Client device 104 creates the trick play index based on container files as they are downloaded during the normal streaming/playback sequence described above. The trick play index identifies, among other things, (i) a network location (i.e., network address) of each key frame embedded in each of the downloaded container files, (ii) a time code associated with each of the key frames, e.g., the time code of the container file in which the identified key frame is embedded, and (iii) a size of the key frame. This information enables client device 104 to access and download the key frame without having to download other data in the container file.
At 440, assume the user selects the rewind trick play feature while client device 104 is performing the normal playback of content associated with a current or latest time code.
At 442, in response to the rewind request, client device 104 determines key frames that are associated with time codes less than the latest or current time code as indicated in the trick play index, and then downloads the determined key frames from their network locations, i.e., from the container files in which the key frames are embedded, as indicated in the index. The downloading includes downloading the key frames from their respective container files, without downloading the non-key frames. In other words, client device 104 downloads only the key frames to implement the trick play feature.
At 444, client device 104 plays back the downloaded key frames (i.e., decodes and then presents the content recovered therefrom) in a rewind play direction, i.e., in an order of decreasing time code beginning with the current or latest time code.
The trick play sequence 442, 444 repeats.
At any time during the trick play sequence, the user may select to exit the trick play feature, e.g., exit rewind, and resume normal streaming and playback. Alternatively, the user may select a subsequent trick play feature, such as fast forward.
Assume, for example, that the user selects fast forward during the rewind. In response to the fast forward request, the rewind is stopped after the playback of content from a key frame associated with a last time code that is less than the current time code (since rewind plays back content in an order of decreasing time code beginning with the current time code).
Then, trick play sequence 442, 444 repeats to implement the fast forward, as follows.
At 442, client device 104 determines key frames associated with time codes greater than the last time code as indicated in the trick play index, and then downloads the determined key frames (but not the non-key frames) from their network locations as also indicated in the index.
At 444, the key frames downloaded at 442 are played back in the forward direction beginning with the last time code, toward the current time.
During trick play, the key frames may be played back at the same rate at which the video was originally captured and encoded, e.g., at a rate of 30 fps or at a slower frame rate. To implements a faster rewind or trick play, key frames may be skipped, e.g., every other key frame identified in the trick play index may be played back.
3.4 Trick Play Index Stored Offsite
In an embodiment, the trick play index created by client device 104 may be stored in and offsite location in network services 102 for subsequent access by the client device on an as needed basis to implement the trick play features.
FIG. 4B is a sequence diagram 480 corresponding to such an embodiment. Sequence diagram 480 is similar to sequence diagram 400, except for the following additional interactions between client device 104 and network services 102.
At 482, after client device 104 has created the trick play index, the client device uploads the trick play index to network services 102 (over communication network 106) for storage at a network location therein. For example, client device 104 may upload the trick play index to either RTS 114 or CDN 112.
At 484, after client device 104 receives the trick play request at 440, the client device 104 downloads the trick play index from network services 102, e.g., from either RTS 114 or CDN 112.
Once the trick play index has been downloaded, it is available for use to implement the requested trick play feature in client device 104.
4 Profile and Playlist Messages
4.1 Profile Message
FIG. 5 is an example Profile message 500. In an embodiment, the Profile message format is in accordance with the World Wide Web Consortium (W3C) recommended Extensible Markup Language (XML) markup language, Synchronized Multimedia Integration Language (SMIL) 3.0 Tiny profile. This profile is well-suited to descriptions of web-based multimedia. However, other protocols may be used to format the Profile message.
Profile message 500 includes a header 501 to specify the base profile as SMIL 3.0 (Tiny), and a body including video encoding (VE) profiles 502 and 504, and an audio encoding (AE) profile 506. Profile message 500 corresponds to a requested program ID, such as encoded program 200 of FIG. 2. Each of VE profiles 502 and 504 specifies the following encoding settings or parameters:

    
    
        a. a content type, e.g., video;
        b. an encoding level “Video ID” (e.g., level 1=L2, level 2=L2) with its corresponding
        
            i. encoding bitrate (e.g., Rate1 or Rate2, such as a bitrate=400000 bps or 6000000 bps), and
            ii. video resolution (e.g., Res1 or Res2) in terms of, e.g., pixel width and height dimensions (e.g., 768×432); and
        
        
        c. MIME type.
    
    


Similarly, AE profile 906 specifies:

    
    
        a. a content type, e.g., audio;
        b. an encoding bitrate/reserved bandwidth value (e.g., 192000); and
        c. a MIME type.

4.2 Playlist Message

    
    


FIG. 6 is an example Playlist message 600 generated in response to a GetPlaylist message selection criteria including a current time of 40 (seconds) and specifying a level 1 encoding level. Like the Profile message, the Playlist message is formatted in accordance with SMIL 3.0.
Playlist message 600 includes a header 601 to specify the base profile as 3.0, and a body that includes sequential records or elements 602-610, each of which is defined as a seq element <seq>. In an embodiment, each seq element 602-610 corresponds to an uploaded container file. Using seq elements, RTS 114 is able to specify a sequence of real-time media streams for playback. A sequence tag is used with each element to indicate one of <video>, <audio> or <subtitle/text> encoded content for streaming. Elements 602-610 identify respective uploaded elements (e.g., container files) that meet the Playlist message criteria (i.e., encoding level 1 and a time code equal to or greater than 40). In the example of FIG. 6, elements 602-608 identify three container files containing successive or time-ordered two second blocks of encoded video. Element 610 identifies a container file containing a two second segment of encoded audio. Each of the Playlist message records 602-610 includes:

    
    
        a. a content type identifier (e.g., video or audio);
        b. a URL of the identified container file (e.g., src=http://10.180.14.232/1140.mkv). For example, the URLs correspond to container file addresses from the list of addresses A1 or A2 from FIG. 2;
        c. a time code in seconds (e.g., a start time and an end time, referred to as “ClipBegin” and “ClipEnd,” respectively,) associated with the segment encoded in the identified container file. The example time codes for each of the container files are 40-42, 42-44, and 46-48); and
        d. a file size of the identified container file (e.g., 3200 kilobits).

5 Trick Play Index

    
    


FIG. 7 is an illustration of an example trick play index 700 created in client device 104 during normal streaming and playback which may be accessed by the client device to implement a trick play feature.
Trick play index 700 includes a list of key frame (KF) records 701, each identifying a corresponding one of key frames KF 1-N included in a corresponding one of successive container files CF 1-N. Each KF record 701 includes:

    
    
        a. a time code TC corresponding to the container file in which the key frame is included;
        b. a network address, e.g., URL, of the container file in which the key frame is included;
        c. a file offset, such as a byte offset, of the key frame from a beginning, e.g., URL, of the container file in which key frame is included; and
        d. a size, e.g., in bytes, of the key frame.
    
    


Together, the network address and the offset in each record 701 represent, or indicate, a location where the corresponding key frame may be accessed by the client device. The size indicates, e.g., the number of bytes that must be downloaded.
6 Method Flowcharts
6.1 Trick Play with Trick Play Index
FIG. 8 is a flowchart of an example method 800 of using a trick play index to implement trick play features in client device 104, while the client device is streaming multimedia content. Method 800 is in accordance with sequences 400 and 480 of FIGS. 4A and 4B, and may be implemented in client device 104. The multimedia content includes video, and may also include audio and/or text (e.g., subtitles). Method 800 may be implemented in any of the contexts of on-demand, live, and real-time streaming.
Method 800 assumes client device 104 has already initiated a streaming session to stream a requested multimedia video program from network services 102 over network 106, in accordance with the start-up sequence of FIGS. 4A and 4B, and the streaming session is in progress.
805 includes sending a playlist request (e.g., a GetPlaylist message) relating to the requested video program to network services 102 (e.g., RTS 114) over communication network 106. The playlist request includes file selection criteria that includes a current time and specifies an encoding level (corresponding to an encoding bit rate and resolution) suitable for the client device.
810 includes receiving a playlist (e.g., a Playlist message), from network services 102 identifying encoded files in CDN 112 for the requested program that match the selection criteria, i.e., that are associated with successive time codes greater than the current time, and correspond to the specified encoding level. The playlist includes, for each identified file, an address of the file, and a time code associated with the file.
815 includes downloading the files of encoded video (including their key and non-key frames) identified in the playlist from their respective addresses in, e.g., CDN 112. Each of the files includes encoded video frames. The encoded video frames include non-key frames and key frames interspersed among the non-key frames.
820 includes playing back the video from each of the downloaded files, including the video from the key-frames and non-key frames in each of the files. The playing back includes playing back the video from each of the downloaded files in a forward direction, i.e., in an order of increasing time code.
825 includes creating a trick play index (e.g., trick play index 700 in FIG. 7) from the downloaded files. In an embodiment, the creating includes creating the trick play request incrementally as each file is downloaded. The trick play index indicates network locations, e.g., addresses, of the key frames in their respective files in CDN 112.
830 includes receiving a trick play request from the user of the client device, such as a request to rewind or fast forward through video.
In response to the trick play request, method 800 performs the next operations 835 and 840.
835 includes downloading the key frames, but not the non-key frames, from the key frame network locations indicated in the trick play index.
840 includes playing back the video from the downloaded key frames (not from non-key frames).
If the trick play request is rewind, then 840 includes playing back the key frames in a rewind direction, i.e., in an order of successively decreasing time codes.
If the trick play request is fast forward, then 840 includes playing back the key frames in the forward direction, i.e., in the order of successively increasing time codes.
In an embodiment in which the trick play index is stored in an offsite location, the following additional operations are performed:

    
    
        a. after creating the trick play index at 825, transmitting the trick play index to a network address (of the offsite location) over the communication network; and
        b. in response to receiving the trick play request at 830, downloading the trick play request from the offsite location so that it is available for use in operations 835 and 840.

6.2 Creating a Trick Play Index

    
    


FIG. 9 is a flowchart of an example method 900 of creating a trick play index. Method 900 expands on operation 825 of method 800. Client device 104 parses each container file after it is downloaded to create records in the trick play index, in the following manner.
905 includes accessing the time stamp and the address, e.g., URL, associated with a downloaded container file, e.g., from the Playlist message that referenced the container file.
910 includes determining an offset, e.g., in bytes, of the key frame in the container file from the beginning of the container file. Such determining may include traversing the K/NK flags sequentially in the container file to locate the instance of the key frame (or of multiple key frames) in the container file.
915 includes determining a size, e.g., in bytes, of the key frame. For example, the size determining may include determining a total number of bytes between a K/NK flag indicating a start of a key frame and a subsequent K/NK flag indicating a start of a non-key frame immediately following the key frame.
920 includes storing the accessed URL and time code, and the determined offset and size of the key frame in a new record of the trick play index.
930 includes repeating operations 905-920 for each next downloaded container file.
7 Systems
FIG. 10 is a block diagram of a computer system 1000 configured to support/perform streaming and trick play features as described herein.
Computer system 1000 includes one or more computer instruction processing units and/or processor cores, illustrated here as processor 1002, to execute computer readable instructions, also referred to herein as computer program logic.
Computer system 1000 may include memory, cache, registers, and/or storage, illustrated here as memory 1004, which may include a non-transitory computer readable medium encoded with computer programs, illustrated here as computer program 1006.
Memory 1004 may include data 1008 to be used by processor 1002 in executing computer program 1006, and/or generated by processor 1002 during execution of computer program 1006. Data 1008 may include container files 1008a and at trick play index 1008b, such as used in the methods described herein.
Computer program 1006 may include:
Client application instructions 1010 to cause processor 1002 to perform client device functions as described herein. Instructions 1010 include:
GUI instructions 1012 to implement a GUI through which a user may select to stream a program and select trick play features;
streaming and playback 1014 instructions to download, decode, and playback streamed video content; and
trick play instructions 1016 to create and use a trick play index to implement trick play features.
Instructions 1010-1016 cause processor 1002 to perform functions such as described in one or more examples above.
Methods and systems disclosed herein may be implemented with respect to one or more of a variety of systems including one or more consumer systems, such as described below with reference to FIGS. 11 and 12. Methods and systems disclosed herein are not, however, limited to the examples of FIGS. 11 and 12.
FIG. 11 is a block diagram of an example computer system 1100 corresponding to any of network services 102, including encoder 110, CDN 112, and RTS 114. Computer system 1100, which may be, e.g., a server, includes one or more processors 1105, a memory 1110 in which instruction sets and databases for computer program applications are stored, a mass storage 1120 for storing, e.g., encoded programs, and an input/output (I/O) module 1115 through which components of computer system 1100 may communicate with communication network 106.
FIG. 12 is a block diagram of an example system 1200 representing, e.g., client device 104, and may be implemented, and configured to operate, as described in one or more examples herein.
System 1200 or portions thereof may be implemented within one or more integrated circuit dies, and may be implemented as a system-on-a-chip (SoC).
System 1200 may include one or more processors 1204 to execute client-side application programs stored in memory 1205.
System 1200 may include a communication system 1206 to interface between processors 1204 and communication networks, such as networks 106. Communication system 1206 may include a wired and/or wireless communication system.
System 1200 may include a stream processor 1207 to process program (i.e., content) streams, received over channel 1208 and through communication system 1206, for presentation at system 1200. Stream processor 1207 includes a buffer 1207a to buffer portions of received, streamed programs, and a decoder 1207b to decode and decrypt the buffered programs in accordance with encoding and encryption standards, and using decryption keys. In an alternative embodiment, decoder 1207b may be integrated with a display and graphics platform of system 1200. Stream processor 1207 together with processors 1204 and memory 1205 represent a controller of system 1200. This controller includes modules to perform the functions of one or more examples described herein, such as a streaming module to stream programs through communication system 1206.
System 1200 may include a user interface system 1210.
User interface system 1210 may include a monitor or display 1232 to display information from processor 1204, such as a client-side GUI.
User interface system 1210 may include a human interface device (HID) 1234 to provide user input to processor 1204. HID 1234 may include, for example and without limitation, one or more of a key board, a cursor device, a touch-sensitive device, and or a motion and/or image sensor. HID 1234 may include a physical device and/or a virtual device, such as a monitor-displayed or virtual keyboard.
User interface system 1210 may include an audio system 1236 to receive and/or output audible sound.
System 1200 may correspond to, for example, a computer system, a personal communication device, and/or a television set-top box.
System 1200 may include a housing, and one or more of communication system 1206, processors 1204, memory 1205, user interface system 1210, or portions thereof may be positioned within the housing. The housing may include, without limitation, a rack-mountable housing, a desk-top housing, a lap-top housing, a notebook housing, a net-book housing, a set-top box housing, a portable housing, and/or other conventional electronic housing and/or future-developed housing. For example, communication system 1202 may be implemented to receive a digital television broadcast signal, and system 1200 may include a set-top box housing or a portable housing, such as a mobile telephone housing.
Methods and systems disclosed herein may be implemented in circuitry and/or a machine, such as a computer system, and combinations thereof, including discrete and integrated circuitry, application specific integrated circuitry (ASIC), a processor and memory, and/or a computer-readable medium encoded with instructions executable by a processor, and may be implemented as part of a domain-specific integrated circuit package, a system-on-a-chip (SOC), and/or a combination of integrated circuit packages.
Methods and systems are disclosed herein with the aid of functional building blocks illustrating functions, features, and relationships thereof. At least some of the boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries may be defined so long as the specified functions and relationships thereof are appropriately performed. While various embodiments are disclosed herein, it should be understood that they are presented as examples. The scope of the claims should not be limited by any of the example embodiments disclosed herein.

## Claims

1. A method of video playback with trick play, the method performed by a playback device, the method comprising:
streaming video at a playback device, wherein streaming video comprises:
downloading, at the playback device, blocks of encoded video including a plurality of interspersed key frames, wherein the blocks of encoded video are downloaded from a remote content source over a communication network,
playing back video from the downloaded blocks of encoded video at the playback device; and
incrementally creating a trick play index as each block of encoded video is downloaded at the playback device by identifying network locations of the downloaded blocks of encoded video and parsing each downloaded block of encoded video to determine an offset from the beginning of the downloaded block to a key frame within the downloaded block of encoded video;

storing the created trick play index at the playback device, wherein the stored trick play index indicates the network locations of the downloaded blocks of encoded video and the offsets for the key frames within the downloaded blocks of encoded video; and
receiving a trick play request at the playback device and, in response to the trick play request:
downloading, at the playback device, key frames using the network locations and the offsets indicated in the previously stored trick play index, and
playing back video from the downloaded key frames at the playback device.

2. The method of claim 1, wherein the encoded video comprises successive encoded video frames, including:
non-key frames each encoded based on one or more other video frames of the encoded video; and
the key frames interspersed among the non-key frames, each of the key frames encoded independent of other video frames of the encoded video, and thereby capable of being decoded independent of the other video frames.

3. The method of claim 2, wherein the key frames include intra-coded I-frames and the non-key frames include inter-coded P-frames.

4. The method of claim 2, wherein:
the playing back video from the downloaded blocks of encoded video includes:
decoding the non-key frames and the key frames in the downloaded blocks of encoded video to recover the video encoded therein, and
presenting the recovered video; and

the playing back video from the downloaded key frames includes:
decoding the downloaded key frames to recover the video encoded therein, and
presenting the recovered video.

5. The method of claim 1, further comprising:
prior to the downloading the blocks of encoded video, receiving a playlist over the communication network, the playlist listing network addresses where the blocks of encoded video are accessible; and
wherein downloading the blocks of encoded video includes downloading the blocks of encoded video from the network addresses listed in the playlist.

6. The method of claim 1, wherein the creating the trick play index includes, for each downloaded block of encoded video:
determining a size of the key frame within the downloaded block; and
storing, in the index, the offset and the size of the key frame,
wherein the network address of the block of encoded video and the offset of the key frame together represent one of the indicated network locations within the trick play index.

7. The method of claim 1, wherein:
the downloaded as blocks of encoded video, and correspondingly the key frames interspersed therein, are associated with successive time codes;
the playing back video from the downloaded blocks of encoded video includes playing back the video from the downloaded blocks of encoded video in a forward direction of increasing time codes; and
the playing back in response to the trick play request includes playing back the downloaded key frames in a rewind direction of decreasing time codes.

8. The method of claim 7, further comprising:
receiving a subsequent trick play request and, in response thereto:
downloading further key frames from network addresses indicated in the stored trick play index; and
playing back video from the downloaded further key frames in the forward direction of increasing time codes.

9. The method of claim 1, further comprising:
after creating the trick play index and before receiving the trick play request, uploading the trick play index to a particular network address; and
after receiving the trick play request and before downloading the key frames, downloading the trick play index from the particular network address.

10. An apparatus for video playback with trick play, comprising:
a processor;
a memory storing an application;
wherein the application directs the processor to:
download blocks of encoded video including a plurality of interspersed key frames, wherein the blocks of encoded video are downloaded from a remote content source over a communication network;
play back video from the downloaded blocks of encoded video;
incrementally create a trick play index as each block of encoded video is downloaded at the apparatus for video playback by identifying network locations of the downloaded blocks of encoded video and parsing each downloaded block of encoded video to determine an offset from the beginning of the downloaded block to a key frame within the downloaded block;
store the created trick play index, wherein the stored trick play index indicates the network locations of the downloaded blocks of encoded video and the offsets for the key frames within the downloaded blocks of encoded video; and
receive a trick play request and, in response to the trick play request:
download key frames using the network locations and the offsets indicated in the previously stored trick play index, and
play back video from the downloaded key frames.

11. The apparatus of claim 10, wherein the encoded video comprises successive encoded video frames, including:
non-key frames each encoded based on one or more other video frames; and
the key frames interspersed among the non-key frames, each of the key frames encoded independent of other video frames, and thereby capable of being decoded independent of the other video frames.

12. The apparatus of claim 11, wherein the key frames include intra-coded I-frames and the non-key frames include inter-coded P-frames.

13. The apparatus of claim 10, wherein the application further directs the processor:
prior to when the blocks of encoded video are downloaded, receive a playlist over the communication network, the playlist listing network addresses where the blocks of encoded video are accessible; and
wherein the application further directs the processor to download the blocks of encoded video from the network addresses listed in the playlist.

14. The apparatus of claim 10, wherein the application further directs the processor to, for each downloaded block of encoded video:
determine a size of the key frame within the downloaded block; and
store, in the index, the offset and the size of the key frame,
wherein the network address of the block of encoded video and the offset of the key frame together represent one of the indicated network locations within the trick play index.

15. The apparatus of claim 10, wherein:
the downloaded blocks of encoded video, and correspondingly the key frames interspersed therein, are associated with successive time codes;
the application further directs the processor to play back the video from the downloaded blocks of encoded video in a forward direction of increasing time codes; and
the application further directs the processor to play back the downloaded key frames in a reverse direction of decreasing time codes in response to the trick play request.

16. The apparatus of claim 15, wherein the application further directs the processor to:
receive a subsequent trick play request and, in response thereto:
download further key frames from network addresses indicated in the stored trick play index, and
play back video from the downloaded further key frames in the forward direction of increasing time codes.

17. The apparatus of claim 10, further comprising:
a communication system to communicate with the communication network;
a user interface system; and
a housing to house the processor system, the communication system, and the user the interface system.

18. The apparatus of claim 17, wherein:
the communication system includes a wireless communication system; and
the housing includes a mobile hand-held housing to house the processor system, the communication system, the user interface system, and a battery.

19. A non-transitory computer readable medium encoded with a computer program including instructions to cause a processor of a playback device to:
stream video, wherein the instructions to stream video further comprise instructions to:
download blocks of encoded video including a plurality of interspersed key frames, wherein the blocks of encoded video are downloaded from a remote content source over a communication network;
play back video from the downloaded blocks of encoded video;
during execution of the instructions to stream video, incrementally create a trick play index as each block of encoded video is downloaded by identifying network locations of the downloaded blocks of encoded video and parsing each downloaded block of encoded video to determine an offset from the beginning of the downloaded block to a key frame within the downloaded block;

store the created trick play index, wherein the stored trick play index indicates the network locations of the downloaded blocks of encoded video and the offsets for the key frames within the downloaded blocks of encoded video; and
receive a trick play request and, in response to the trick play request:
downloading key frames using the network locations and the offsets indicated in the previously stored trick play index, and
playing back video from the downloaded key frames.

20. The computer program product of claim 19, wherein the encoded video comprises successive encoded video frames, including:
non-key frames each encoded based on one or more other video frames of the encoded video; and
the key frames interspersed among the non-key frames, each of the key frames encoded independent of other video frames of the encoded video, and thereby capable of being decoded independent of the other video frames.

21. The computer program product of claim 20, wherein the key frames include intra-coded I-frames and the non-key frames include inter-coded P-frames.

22. The computer program product of claim 19, wherein the instructions further include instructions to cause the processor to:
prior to the downloading the blocks of encoded video, receive a playlist over the communication network, the playlist listing network addresses where the blocks of encoded video are accessible; and
wherein the instruction to cause the processor to download the blocks of encoded video further include instructions to cause the processor to download the blocks of encoded video from the network addresses listed in the playlist.

23. The computer program product of claim 19, wherein the instruction to cause the processor to create the trick play index further include instructions to cause the processor to, for each downloaded block of encoded video:
determine a size of the key frame within the downloaded block; and
store, in the index, the offset and the size of the key frame,
wherein the network address of the block of encoded video and the offset of the key frame together represent one of the indicated network locations within the trick play index.

24. The computer program product of claim 19, wherein:
the downloaded as blocks of encoded video, and correspondingly the key frames interspersed therein, are associated with successive time codes;
the instructions to cause the processor to playback video from the downloaded blocks of encoded video further include instructions to cause the processor to playback the video from the downloaded blocks of encoded video in a forward direction of increasing time codes; and
the instructions to cause the processor to playback in response to the trick play request further include instructions to cause the processor to playback the downloaded key frames in a rewind direction of decreasing time codes.

25. The computer program product of claim 24, wherein the instructions further include instructions to cause the processor to:
receive a subsequent trick play request and, in response thereto,
download further key frames from network addresses indicated in the stored trick play index; and
play back video from the downloaded further key frames in the forward direction of increasing time codes.