我们正在使用Scala，WebRTC和Java SDK开发一个Android应用程序。我们当前的任务包括接收被呼叫者启用视频后在第二次SDP协商中发送的远程轨道。因此，呼叫者正在以对等连接观察者的onAddTrack方法访问该视频轨道。实际上，该轨道包含在MediaStreams数组中，然后我们就可以通过ProxySink将其附加到VideoRenderer上，非常类似于此示例：https://webrtc.googlesource.com/src/+/refs/heads/master/examples/androidapp/src/org/appspot/apprtc/CallActivity.java#133。
这是负责此操作的代码段
override def onAddTrack(rtpReceiver: RtpReceiver, mediaStreams: Array[MediaStream]): Unit = {
info("FLOW: onAddTrack")
rtpReceiver.SetObserver(rtpObserver)
call.getCallType match {
case BothVideo(CallRoles.Caller) | RecvPeerVideo(CallRoles.Caller) => {
if (mediaStreams.size > 0) {
val mediaStream = mediaStreams(0)
val videoTracks: Buffer[VideoTrack] = mediaStream.videoTracks.asScala
this.remoteMediaStream = Some(mediaStream)
info(s"FLOW: onAddTrack, call-type: ${call.getCallType}")
if (call.callerShouldReceiveVideo(call.getCallType) && videoTracks.size > 0) {
info(s"FLOW: onAddTrack, enabling video-track")
val videoTrack: VideoTrack = videoTracks(0)
mediaStream.addPreservedTrack(videoTrack)
videoTrack.setEnabled(true)
videoTrack.addSink(flowManager.remoteProxySink)
...
}
}
}
问题是我们无法从被呼叫者的远程轨道获取帧，这有点令人惊讶，因为我们已经能够成功设置呼叫者的远程轨道并在呼叫者发起呼叫时渲染帧。视频，并且必须将远程轨道发送给被调用方。
在创建答案时，我们检测到在SdpObserver集合中调用setLocalDescription后立即在MediaStream（https://webrtc.googlesource.com/src/+/refs/heads/master/sdk/android/api/org/webrtc/MediaStream.java#75）上调用了dispose，我们认为这可能是导致问题的原因。
创建答案：
pcConn.setRemoteDescription(sdpObserver, sdp)
peerConn.createAnswer(sdpObserver, WebRTCCall.sdpMediaConstraints())
在SdpObserver中：
override def onCreateSuccess(sdp: SessionDescription) = {
...
peerConn.setLocalDescription(this, sdp)
...
}
什么可以触发本地setLocalDescription内部的MediaStream.dispose方法？
更新 我们在sdp中发现了一些有趣的东西，视频轨道似乎有发送方向。
v=0
o=- 2191449863069826960 3 IN IP4 127.0.0.1
s=-
t=0 0
a=group:BUNDLE 0 1 2 3
a=msid-semantic: WMS stream0
m=audio 56825 UDP/TLS/RTP/SAVPF 111 103 9 102 0 8 105 13 110 113 126
c=IN IP4 35.167.127.194
a=rtcp:9 IN IP4 0.0.0.0
a=candidate:2294452033 1 udp 2122260223 192.168.2.159 60968 typ host generation 0 network-id 3 network-cost 10
a=candidate:559267639 1 udp 2122202367 ::1 39373 typ host generation 0 network-id 2
a=candidate:1510613869 1 udp 2122129151 127.0.0.1 56438 typ host generation 0 network-id 1
a=candidate:1876313031 1 tcp 1518222591 ::1 59473 typ host tcptype passive generation 0 network-id 2
a=candidate:344579997 1 tcp 1518149375 127.0.0.1 47922 typ host tcptype passive generation 0 network-id 1
a=candidate:842163049 1 udp 1686052607 201.233.49.70 60968 typ srflx raddr 192.168.2.159 rport 60968 generation 0 network-id 3 network-cost 10
a=candidate:1600295039 1 udp 41885439 35.167.127.194 56825 typ relay raddr 201.233.49.70 rport 60968 generation 0 network-id 3 network-cost 10
a=candidate:3811514541 1 udp 41885695 34.221.141.99 60923 typ relay raddr 201.233.49.70 rport 60968 generation 0 network-id 3 network-cost 10
a=ice-ufrag:GGkb
a=ice-pwd:owqpzSht95NQb92cgzKNkQmJ
a=ice-options:trickle renomination
a=fingerprint:sha-256 45:76:5A:81:C1:CD:6B:C8:17:C6:CB:7B:20:CD:C6:DD:59:A3:DC:11:47:78:D3:E1:E1:EE:55:1F:83:A5:32:E4
a=setup:passive
a=mid:0
a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level
a=extmap:2 http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=extmap:5 urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id
a=sendrecv
a=msid:stream0 audio0
a=rtcp-mux
a=rtpmap:111 opus/48000/2
a=rtcp-fb:111 transport-cc
a=fmtp:111 minptime=10;useinbandfec=1
a=rtpmap:103 ISAC/16000
a=rtpmap:9 G722/8000
a=rtpmap:102 ILBC/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:105 CN/16000
a=rtpmap:13 CN/8000
a=rtpmap:110 telephone-event/48000
a=rtpmap:113 telephone-event/16000
a=rtpmap:126 telephone-event/8000
a=ssrc:1249625177 cname:IgXNTJvPXp2HndWi
m=video 9 UDP/TLS/RTP/SAVPF 96 97 98 99 100 101 127
c=IN IP4 0.0.0.0
a=rtcp:9 IN IP4 0.0.0.0
a=ice-ufrag:GGkb
a=ice-pwd:owqpzSht95NQb92cgzKNkQmJ
a=ice-options:trickle renomination
a=fingerprint:sha-256 45:76:5A:81:C1:CD:6B:C8:17:C6:CB:7B:20:CD:C6:DD:59:A3:DC:11:47:78:D3:E1:E1:EE:55:1F:83:A5:32:E4
a=setup:passive
a=mid:1
a=extmap:14 urn:ietf:params:rtp-hdrext:toffset
a=extmap:13 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time
a=extmap:12 urn:3gpp:video-orientation
a=extmap:2 http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01
a=extmap:11 http://www.webrtc.org/experiments/rtp-hdrext/playout-delay
a=extmap:6 http://www.webrtc.org/experiments/rtp-hdrext/video-content-type
a=extmap:7 http://www.webrtc.org/experiments/rtp-hdrext/video-timing
a=extmap:8 http://tools.ietf.org/html/draft-ietf-avtext-framemarking-07
a=extmap:9 http://www.webrtc.org/experiments/rtp-hdrext/color-space
a=extmap:3 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
a=extmap:5 urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id
a=sendonly
a=msid:stream0 video0
a=rtcp-mux
a=rtcp-rsize
a=rtpmap:96 VP8/90000
a=rtcp-fb:96 goog-remb
a=rtcp-fb:96 transport-cc
a=rtcp-fb:96 ccm fir
a=rtcp-fb:96 nack
a=rtcp-fb:96 nack pli
a=rtpmap:97 rtx/90000
a=fmtp:97 apt=96
a=rtpmap:98 VP9/90000
a=rtcp-fb:98 goog-remb
a=rtcp-fb:98 transport-cc
a=rtcp-fb:98 ccm fir
a=rtcp-fb:98 nack
a=rtcp-fb:98 nack pli
a=rtpmap:99 rtx/90000
a=fmtp:99 apt=98
a=rtpmap:100 red/90000
a=rtpmap:101 rtx/90000
a=fmtp:101 apt=100
a=rtpmap:127 ulpfec/90000
a=ssrc-group:FID 1487952389 3127747783
a=ssrc:1487952389 cname:IgXNTJvPXp2HndWi
a=ssrc:3127747783 cname:IgXNTJvPXp2HndWi
m=application 9 DTLS/SCTP 5000
c=IN IP4 0.0.0.0
b=AS:30
a=ice-ufrag:GGkb
a=ice-pwd:owqpzSht95NQb92cgzKNkQmJ
a