p2p sample code breaks with latest M104: preferCodecs causes setLocal/RemoteDescription error: Failed to parse: "". Reason: Failed to parse audio codecs correctly.

[chenzx]

Due to networking limit, i cannot build OWT android sdk, so i use a prebuilt 3rd bundle: https://github.com/webrtc-sdk/android

I do not use the owt-server but write a simple nodejs version for test. (The server part should be irrelevant, since it only forwards signaling messages)

& Also due to only 1 android emulator there, i modified the p2p client sample code to let Activity contains 2 clients: one for publisher, the other consumer.

The key WebRTC signaling setup is:

1. publisher call createOffer to get SDP offer
2. publisher call preferCodecs to modify the SDP <--- HERE
3. publisher call setLocalDescription and then send SDP to consumer via signaling server
4. consumer receives SDP and call setRemoteDescription

The preferCodecs is very problematic, since it add 2 codecs for audio & video: ~/repo/open-webrtc-toolkit/owt-client-android/src/sdk/base/src/main/java/owt/base/PeerConnectionChannel.java

    private SessionDescription preferCodecs(SessionDescription sdp, boolean video) {
        LinkedHashSet<String> preferredCodecs = new LinkedHashSet<>();
        if (video) {
            for (VideoCodec codec : this.videoCodecs) {
                preferredCodecs.add(codec.name);
            }
            preferredCodecs.add("red");
            preferredCodecs.add("ulpfec");
        } else {
            for (AudioCodec codec : audioCodecs) {
                preferredCodecs.add(codec.name);
            }
            preferredCodecs.add("CN");
            preferredCodecs.add("telephone-event");
        }
        return preferCodec(sdp, preferredCodecs, video);
    }

Note: I enable the WebRTC logging by Logging.enableLogToDebugOutput(Logging.Severity.LS_VERBOSE);, & AV1 codec needs added to ~/repo/open-webrtc-toolkit/owt-client-android/src/sdk/base/src/main/java/owt/base/MediaCodecs.java

The error log:

...
W/webrtc_sdp.cc: (line 3581): Ignore rtpmap line that did not appear in the <fmt> of the m-line: a=rtpmap:63 red/48000/2
E/webrtc_sdp.cc: (line 414): Failed to parse: "". Reason: Failed to parse audio codecs correctly.

So i remove the preferCodecs logic: ~/repo/open-webrtc-toolkit/owt-client-android/src/sdk/base/src/main/java/owt/base/PeerConnectionChannel.java

    //SdpObserver
    @Override
    public void onCreateSuccess(final SessionDescription sessionDescription) {
        localSdp = sessionDescription;

//        if (audioCodecs != null) {
//            localSdp = preferCodecs(localSdp, false);
//        }
//
//        if (videoCodecs != null) {
//            localSdp = preferCodecs(localSdp, true);
//        }
...

Now p2p connection is successful.

[chenzx]

PS: I'm try using OWT android lib for P2P mode (vs SFU) remote desktop streaming, not for chat.