Last updated: 2021-09-16 10:16:36

    Basics

    This document introduces the live playback feature of the Video Cloud SDK.

    Live streaming and video on demand

    • In live streaming, the video streams published by hosts in real time are the source of streaming. When hosts stop publishing streams, the video played stops. Since video is streamed in real time, players do not have progress bars when they play live streaming URLs.
    • In video on demand (VOD), video files in the cloud are the source of streaming. Videos can be played at any time as long as they are not deleted from the cloud, and the playback progress can be adjusted using the progress bar. Video streaming websites such as Tencent Video and Youku Tudou are typical applications of VOD.

    Supported protocols

    The table below lists the common protocols used for live streaming. We recommend FLV URLs (which start with http and end with flv) for LVB and WebRTC for LEB. For more information, please see LEB.

    Protocol Pro Con Playback Latency
    FLV Mature, well adapted to high-concurrency scenarios SDK integration is required. 2-3s
    RTMP Relatively low latency Poor performance in high-concurrency scenarios 1-3s
    HLS (M3U8) Well supported on mobile browsers High latency 10-30s
    WebRTC Lowest latency SDK integration is required. < 1s
    Note:

    LVB and LEB are priced differently. For details, please see LVB Billing Overview and LEB Billing Overview.

    Notes

    The Video Cloud SDK does not impose any limit on the sources of playback URLs, which means you can use it to play both Tencent Cloud and non-Tencent Cloud URLs. However, the player of the SDK supports only live streaming URLs in FLV, RTMP, HLS (M3U8), and WebRTC formats and VOD URLs in MP4, HLS (M3U8), and FLV formats.

    Sample Code

    Regarding frequently asked questions among developers, Tencent Cloud offers a straightforward API example project, which you can use to quickly learn how to use different APIs.

    Platform GitHub Address
    iOS GitHub
    Android GitHub

    Integration

    Step 1. Create a player object

    The V2TXLivePlayer module in the Video Cloud SDK offers live playback capabilities.

    V2TXLivePlayer *_txLivePlayer = [[V2TXLivePlayer alloc] init];
    

    Step 2. Create a rendering view

    In iOS, a view is used as the basic UI rendering unit. Therefore, you need to configure a view, whose size and position you can adjust, for the player to display video images on.

    // Use setRenderView to bind a rendering view to the player
    [_txLivePlayer setRenderView:_myView];
    

    Technically, the player does not render video images directly on the view (_myView in the sample code) you provide. Instead, it creates a subview for OpenGL rendering over the view.

    You can adjust the size of video images by changing the size and position of the view. The SDK will make changes to the video images accordingly.

    How can I animate views?
    You are allowed great flexibility in view animation, but note that you need to modify the transform rather than frame attribute of the view.

    [UIView animateWithDuration:0.5 animations:^{
    _myView.transform = CGAffineTransformMakeScale(0.3, 0.3); // Shrink by 1/3
    }];
    

    Step 3. Start playback

    NSString* url = @"http://2157.liveplay.myqcloud.com/live/2157_xxxx.flv";
    [_txLivePlayer startPlay:url];
    

    Step 4. Change the fill mode

    • setRenderFillMode: aspect fill or aspect fit
      ValueDescription
      V2TXLiveFillModeFill Images are scaled to fill the entire screen, and the excess parts are cropped. There are no black bars in this mode, but images may not be displayed in whole.
      V2TXLiveFillModeFit Images are scaled as large as the longer side can go. Neither side exceeds the screen after scaling. Images are centered, and there may be black bars.
    • setRenderRotation: clockwise rotation of video
      ValueDescription
      V2TXLiveRotation0 Original
      V2TXLiveRotation90 Rotate 90 degrees clockwise
      V2TXLiveRotation180 Rotate 180 degrees clockwise
      V2TXLiveRotation270 Rotate 270 degrees clockwise

    Step 5. Pause playback

    Technically speaking, you cannot pause a live playback. In this document, by pausing playback, we mean freezing video and disabling audio. In the meantime, new video streams continue to be sent to the cloud. When you resume playback, it starts from the time of resumption. This is in contrast to VOD. With VOD, when you pause and resume playback, the player behaves the same way as it does when you pause and resume a local video file.

    // Pause playback
    [_txLivePlayer pauseAudio];
    [_txLivePlayer pauseVideo];
    // Resume playback
    [_txLivePlayer resumeAudio];
    [_txLivePlayer resumeVideo];
    

    Step 6. Stop playback

    // Stop playback
    [_txLivePlayer stopPlay];
    

    Step 7. Take a screenshot

    Call snapshot to take a screenshot of the live video streamed. You can get the screenshot taken in the onSnapshotComplete callback of V2TXLivePlayerObserver. This method captures a frame of the streamed video. To capture the UI, use the corresponding API of the iOS system.

    ...
    [_txLivePlayer setObserver:self];
    [_txLivePlayer snapshot];
    ...
    - (void)onSnapshotComplete:(id<V2TXLivePlayer>)player image:(TXImage *)image {
      if (image != nil) {
          dispatch_async(dispatch_get_main_queue(), ^{
              [self handle:image];
          });
      }
    }
    

    Latency Control

    The live playback feature of the SDK is not based on FFmpeg, but Tencent Cloud’s proprietary playback engine, which is why the SDK offers better latency control than open-source players do. We provide three latency control modes, which can be used for showrooms, game streaming, and hybrid scenarios.

    • Comparison of the three modes
      ModeStutterAverage LatencyScenarioRemarks
      Speedy More likely than the speedy mode 2-3s Live showroom (Chongding Dahui) The mode delivers low latency and is suitable for latency-sensitive scenarios.
      Smooth Least likely of the three &dxgt;= 5s Game streaming (Penguin Esports) Playback is least likely to stutter in this mode, which makes it suitable for ultra-high-bitrate streaming of games such as PUBG.
      Auto Self-adaptive to network conditions 2-8s Hybrid The better network conditions at the audience end, the lower the latency.
    • Code to integrate the three modes
      // Auto mode
      [_txLivePlayer setCacheParams:1 maxTime:5];
      // Speedy mode
      [_txLivePlayer setCacheParams:1 maxTime:1];
      // Smooth mode
      [_txLivePlayer setCacheParams:5 maxTime:5];
      // Start playback after configuration
      
    Note:

    For more information on stuttering and latency control, see Video Stutter.

    Listening for SDK Events

    You can bind a V2TXLivePlayerObserver to your V2TXLivePlayer object to receive callback notifications about the player status, playback volume, first audio/video frame, statistics, warning and error messages, etc.

    Periodically triggered notifications

    • The onStatisticsUpdate callback notification is triggered every 2 seconds to update you on the player’s status in real time. Like a car’s dashboard, the callback gives you information about the SDK, such as network conditions and video information.
      ParameterDescription
      appCpu CPU usage (%) of the application
      systemCpu CPU usage (%) of the system
      width Video width
      height Video height
      fps Frame rate (fps)
      audioBitrate Audio bitrate (Kbps)
      videoBitrate Video bitrate (Kbps)
    • The onPlayoutVolumeUpdate callback, which notifies you of the player’s volume, works only after you call enableVolumeEvaluation to enable the volume reminder. You can set the interval of the callback by specifying the intervalMs parameter of enableVolumeEvaluation.

    Event-triggered notifications

    Other callbacks are triggered when specific events occur.