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• 句法
• 用法注意事项
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

RTCRtpSender 方法 replaceTrack() replaces the track currently being used as the sender's source with a new MediaStreamTrack . The new track must be of the same media kind (audio, video, etc) and switching the track should not require negotiation.

Among the use cases for replaceTrack() is the common need to switch between the rear- and front-facing cameras on a phone. With replaceTrack() , you can simply have a track object for each camera and switch between the two as needed. See the example Switching cameras 下文。

句法

trackReplacedPromise = sender.replaceTrack(newTrack);
					

参数

newTrack 可选

MediaStreamTrack specifying the track with which to replace the RTCRtpSender 's current source track. The new track's kind must be the same as the current track's, or the replace track request will fail.

返回值

A Promise which is fulfilled once the track has been successfully replaced. The promise is rejected if the track cannot be replaced for any reason; this is commonly because the change would require renegotiation of the codec, which is not allowed (see Things that require negotiation ).

若 newTrack was omitted or was null , replaceTrack() simply stops the sender. No negotiation is required in this case.

When the promise is fulfilled, the fulfillment handler receives a value of undefined .

异常

If the returned promise is rejected, one of the following exceptions is provided to the rejection handler:

InvalidModificationError

替换 RTCRtpSende r 's current track with the new one would require negotiation.

InvalidStateError

The track on which this method was called is stopped rather than running.

TypeError

The new track's kind doesn't match the original track.

用法注意事项

Things that trigger negotiation

Not all track replacements require renegotiation. In fact, even changes that seem huge can be done without requiring negotation. Here are the changes that can trigger negotiaton:

• The new track has a resolution which is outside the bounds of the bounds of the current track; that is, the new track is either wider or taller than the current one.
• The new track's frame rate is high enough to cause the codec's block rate to be exceeded.
• The new track is a video track and its raw or pre-encoded state differs from that of the original track.
• The new track is an audio track with a different number of channels fom the original.
• Media sources that have built-in encoders — such as hardware encoders — may not be able to provide the negotiated codec. Software sources may not implement the negotiated codec.

范例

Switching video cameras

// example to change video camera, suppose selected value saved into window.selectedCamera
navigator.mediaDevices
  .getUserMedia({
    video: {
      deviceId: {
        exact: window.selectedCamera
      }
    }
  })
  .then(function(stream) {
    let videoTrack = stream.getVideoTracks()[0];
    PCs.forEach(function(pc) {
      var sender = pc.getSenders().find(function(s) {
        return s.track.kind == videoTrack.kind;
      });
      console.log('found sender:', sender);
      sender.replaceTrack(videoTrack);
    });
  })
  .catch(function(err) {
    console.error('Error happens:', err);
  });
						

规范

规范	状态	注释
WebRTC 1.0: Real-time Communication Between Browsers The definition of 'RTCRtpSender.replaceTrack()' in that specification.	候选推荐

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
replaceTrack()	Chrome 65	Edge ≤18	Firefox Yes	IE 不支持 No	Opera Yes	Safari Yes	WebView Android 65	Chrome Android 65	Firefox Android Yes	Opera Android Yes	Safari iOS Yes	Samsung Internet Android 9.0

图例

完整支持

完整支持

不支持

不支持

另请参阅

• WebRTC API

元数据

• 最后修改： Mar 18, 2019

相关话题

1. WebRTC API
2. RTCRtpSender
3. 特性

   1. dtmf
   2. track
4. 方法

   1. getParameters()
   2. getStats()
   3. replaceTrack()
   4. setParameters()
5. Related pages for WebRTC

   1. MediaDevices.getUserMedia()
   2. Navigator.mediaDevices
   3. RTCCertificate
   4. RTCDTMFSender
   5. RTCDTMFToneChangeEvent
   6. RTCDataChannel
   7. RTCDataChannelEvent
   8. RTCDtlsTransport
   9. RTCErrorEvent
   10. RTCIceCandidate
   11. RTCIceTransport
   12. RTCPeerConnection
   13. RTCPeerConnectionIceErrorEvent
   14. RTCPeerConnectionIceEvent
   15. RTCRtpReceiver
   16. RTCRtpTransceiver
   17. RTCSctpTransport
   18. RTCSessionDescription
   19. RTCStatsEvent
   20. RTCStatsReport
   21. RTCTrackEvent