tencent cloud

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
HLS	Mature, well adapted to high-concurrency scenarios	SDK integration is required.	3s - 5s
FLV	Mature, well adapted to high-concurrency scenarios	SDK integration is required	2s - 3s
RTMP	Relatively low latency	Poor performance in high-concurrency scenarios	1s - 3s
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
Flutter	Github

Integration

Step 1. Download the SDK

Download the SDK and follow the instructions in SDK Integration to integrate the SDK into your application.

Step 2. Configure License Authorization for SDK

1. Obtain license authorization：
   • If you have obtained the relevant license authorization，need to Get License URL and License Key in Cloud Live Console
     
   • If you have not yet obtained the license authorization，Please reference Adding and Renewing Licenses to make an application.
2. Before your App calls SDK-related functions (it is recommended in the Application class), set the following settings:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  NSString * const licenceURL = @"<your licenseUrl>";
  NSString * const licenceKey = @"<your key>";
   [V2TXLivePremier setEnvironment:@"GDPR"];// set your environment
  // V2TXLivePremier located in "V2TXLivePremier.h"
  [V2TXLivePremier setLicence:licenceURL key:licenceKey];
  [V2TXLivePremier setObserver:self];
  NSLog(@"SDK Version = %@", [V2TXLivePremier getSDKVersionStr]);
  return YES;
}
#pragma mark - V2TXLivePremierObserver
- (void)onLicenceLoaded:(int)result Reason:(NSString *)reason {
  NSLog(@"onLicenceLoaded: result:%d reason:%@", result, reason);
}
@end

Note：

The packageName configured in the license must be the same as the application itself, otherwise the play stream will fail.

Step 3. Create Player

The V2TXLivePlayer module in Tencent Cloud SDK is responsible for implementing the live broadcast function.

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

Step 4. 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 5. Start playback

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

Step 6. Change the fill mode

• setRenderFillMode: aspect fill or aspect fit

  Value	Description
  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

  Value	Description
  V2TXLiveRotation0	Original
  V2TXLiveRotation90	Rotate 90 degrees clockwise
  V2TXLiveRotation180	Rotate 180 degrees clockwise
  V2TXLiveRotation270	Rotate 270 degrees clockwise

Step 7. 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 8. Stop playback

// Stop playback
[_txLivePlayer stopPlay];

Step 9. 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

  Mode	Stutter	Average Latency	Scenario	Remarks
  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	>= 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.

  Parameter	Description
  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.