如何在通话中交换 webrtc 中的相机源（javascript API）

Question

在 iOS 上我可以这样做：

// set a new camera id
cameraId = ([cameraId isEqualToString:frontCameraId]) ? backCameraId : frontCameraId;

// determine if the stream has a video track
BOOL hasActiveVideoTrack = ([self.localMediaStream.videoTracks count] > 0);

// remove video track from the stream
if (hasActiveVideoTrack) {
    [self.localMediaStream removeVideoTrack:self.localVideoTrack];
}

// remove renderer from the video track
[self.localVideoTrack removeRenderer:self.localVideoView];

// re init the capturer, video source and video track
localVideoCapturer = nil;
localVideoSource = nil;
localVideoCapturer = [RTCVideoCapturer capturerWithDeviceName:cameraId];
localVideoSource = [peerConnectionFactory videoSourceWithCapturer:localVideoCapturer constraints:mediaConstraints];

// create a new video track
self.localVideoTrack = [peerConnectionFactory videoTrackWithID:@"ARDAMSv0" source:localVideoSource];
[self.localVideoTrack addRenderer:self.localVideoView];

// add video track back to the stream
if (hasActiveVideoTrack) {
    [self.localMediaStream addVideoTrack:self.localVideoTrack];
}

在前后摄像头之间切换。我可以在通话中调用上面的代码，遥控器将暂时停止接收帧，然后继续接收帧，但现在来自另一台摄像机。我如何在 javascript 中做同样的事情？您不像我在 iOS 中那样专门创建视频轨道，那么如何在不开始新呼叫的情况下告诉流使用不同的摄像头设备？

Answer 1

这是一项实验技术

WebRTC Javascript 代码示例包含一个相机选择示例：

• https://webrtc.github.io/samples/src/content/devices/input-output/

在 github 上提供源代码：

• https://github.com/webrtc/samples
  • https://github.com/webrtc/samples/blob/gh-pages/src/js/adapter.js

使用MediaDevices.enumerateDevices获取视频|音频源（在 chrome 和 firefox 上）

• https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices/enumerateDevices

• MediaStreamTrack.getSources（仅限 chrome）已被弃用，取而代之的是 MediaDevices.enumerateDevices()

navigator.mediaDevices.enumerateDevices =
        navigator.mediaDevices.enumerateDevices || function() {
          return new Promise(function(resolve) {
            var infos = [
              {kind: 'audioinput', deviceId: 'default', label: '', groupId: ''},
              {kind: 'videoinput', deviceId: 'default', label: '', groupId: ''}
            ];
            resolve(infos);
          });
        };

    if (browserDetails.version < 41) {
      // Work around http://bugzil.la/1169665
      var orgEnumerateDevices =
          navigator.mediaDevices.enumerateDevices.bind(navigator.mediaDevices);
      navigator.mediaDevices.enumerateDevices = function() {
        return orgEnumerateDevices().then(undefined, function(e) {
          if (e.name === 'NotFoundError') {
            return [];
          }
          throw e;
        });
      };
    }
  }

要交换相机， @wpp 的@omar-khaled 回答更改 RTCPeerConnection 的媒体流

• https://www.webrtc-experiment.com/docs/how-to-switch-streams.html

_this.rtc.localstream.stop();
_this.rtc.pc.removeStream(_this.rtc.localstream);

gotStream = function (localstream_aud){
var constraints_audio={
    audio:true
   }

_this.rtc.localstream_aud = localstream_aud;
_this.rtc.mediaConstraints= constraints_audio;   
_this.rtc.createOffer();
}
getUserMedia(constraints_audio, gotStream);

gotStream = function (localstream){
var constraints_screen={
        audio:false,
        video:{
            mandatory:{
                chromeMediaSource: 'screen'
            }
        }
    }
  _this.rtc.localstream = localstream;
  _this.rtc.mediaConstraints=constraints_video;


  _this.rtc.createStream();  
  _this.rtc.createOffer();
}
getUserMedia(constraints_video, gotStream);