SDP Offer not generating

[Pavel]

I'm trying to add WebRTC native (M84.4147) into my existing Qt GUI application. 
By now most of my code is based on peerconnection_client example's code. However I'm stuck with generating sdp offer, which does not fire nor CreateSessionDescriptionObserver::OnSuccess nor CreateSessionDescriptionObserver::OnFailure.

In my MainWindow  form I create websocket, which is used for signalling, and conductor

Messanger *rtc = new Messanger(this);
Conductor *conductor = new Conductor(rtc);
rtc->Connect();

Messanger::Connect triggers creating peer_connection by callback. Conductor inherited from webrtc::CreateSessionDescriptionObserver so I expect getting some result in Conductor::OnSuccess or Conductor::OnFailure but this does not happens

void Conductor::OnSignedIn()
{
    peer_connection_factory_ = webrtc::CreatePeerConnectionFactory(
        nullptr /* network_thread */,
        nullptr /* worker_thread */,
        nullptr /* signaling_thread */,
        nullptr /* default_adm */,
        webrtc::CreateBuiltinAudioEncoderFactory(),
        webrtc::CreateBuiltinAudioDecoderFactory(),
         webrtc::CreateBuiltinVideoEncoderFactory(),

         webrtc::CreateBuiltinVideoDecoderFactory(),

         nullptr /* audio_mixer */,

         nullptr /* audio_processing */);

    /* some checks not nullptrs
    ...
    */ 

    webrtc::PeerConnectionInterface::RTCConfiguration config;

    config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;

    config.enable_dtls_srtp = dtls;

    webrtc::PeerConnectionInterface::IceServer server;

    server.uri = "stun:stun.l.google.com:19302";

    config.servers.push_back(server);

    peer_connection_ = peer_connection_factory_->CreatePeerConnection(config, nullptr, nullptr, this);
    peer_connection_->CreateOffer(this, webrtc::PeerConnectionInterface::RTCOfferAnswerOptions());

}

What i'm doing wrong? Is it really threading-related problem? If 
I'll be grateful for any help

[Alexandre GOUAILLARD]

what do your callbacks (the observer::OnSuccess/OnFailure overridden method) look like?

I suppose you are using the new m84 signature which takes the RTCError as an argument?

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• 
  

[Pavel]

I suppose you are using the new m84 signature which takes the RTCError as an argument?

Yes, I'm.

Here is my callbasks

void Conductor::OnSuccess(webrtc::SessionDescriptionInterface* desc)
{
  qDebug() << "OnSuccess";
 
  peer_connection_->SetLocalDescription(DummySetSessionDescriptionObserver::Create(), desc);

  std::string sdp;
  desc->ToString(&sdp);

  Q_EMIT SDPGen(sdp);
}

void Conductor::OnFailure(webrtc::RTCError error) {
  qDebug() << ToString(error.type()) << ": " << error.message();
}

Actually, I already fix part of my problem. It was tied to threading. Adding new signaling thread for webrtc::CreatePeerConnectionFactory was a solution

But I still have some problems. For now, my offer looks like this:

v=0
o=- 5454879051792501191 2 IN IP4 127.0.0.1
s=-
t=0 0
a=group:BUNDLE 0 1
a=msid-semantic: WMS stream_id

But there is no media info, nor ICE candidates. I add tracks before creating offer.

void Conductor::AddTracks() {
    rtc::scoped_refptr<webrtc::AudioTrackInterface> audio_track(
                peer_connection_factory_->CreateAudioTrack(
                    kAudioLabel, peer_connection_factory_->CreateAudioSource(
                        cricket::AudioOptions())));
    auto result_or_error = peer_connection_->AddTrack(audio_track, {kStreamId});
    if (!result_or_error.ok()) {
        qDebug() <<  "Failed to add audio track to PeerConnection: " << result_or_error.error().message();
    }

    rtc::scoped_refptr<CapturerTrackSource> video_device = CapturerTrackSource::Create();
    if (video_device) {
        rtc::scoped_refptr<webrtc::VideoTrackInterface> video_track_(
                    peer_connection_factory_->CreateVideoTrack(kVideoLabel, video_device));
       
        // TODO start rendering

        result_or_error = peer_connection_->AddTrack(video_track_, {kStreamId});

        if (!result_or_error.ok()) {
            qDebug() << "Failed to add video track to PeerConnection: " << result_or_error.error().message();
        }
    } else {
        qDebug() << "OpenVideoCaptureDevice failed";
    }
}

среда, 24 июня 2020 г., 2:14:01 UTC+3 пользователь Alexandre GOUAILLARD написал:

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[Alexandre GOUAILLARD]

It is normal not to have ICE candidate in the offer / answer by default.

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[Pavel]

As I found out Ice candidates can be obtained in PeerConnectionObserver::OnIceCandidate callback.

I continue my experiments and notice that sometimes my offer looks like that

v=0

o=- 99157163530396358 2 IN IP4 127.0.0.1

s=-

t=0 0

a=group:BUNDLE 0 1

a=msid-semantic: WMS stream_id

m=audio 9

 or like that

v=0

o=- 99157163530396358 5 IN IP4 127.0.0.1

s=-

t=0 0

a=group:BUNDL

So, what leeds to this behavior? What I have to do?

среда, 24 июня 2020 г., 15:42:52 UTC+3 пользователь Alexandre GOUAILLARD написал:

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[Pavel]

I add more logging and find out that PeerConnectionObserver and CreateSessionDescriptionObserver callbacks works in same thread, while condictor runs in another.

Is it correct behavior? How can I make my callback to not interrupt each other?

среда, 24 июня 2020 г., 17:14:10 UTC+3 пользователь Pavel написал:

[gfield]

I am having the same problem.. Did you figure out what was happening ?

[V I]

These issues usually appear when you try to squeeze peerconnection_client into your own threading model. Those callbacks work via tasks posted on the current thread, so to make things work you need to use rtc::Thread::Run (https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/examples/peerconnection/client/linux/main.cc;l=109) as your work loop or do what Thread::Run() does yourself - call rtc::Thread::Current()->ProcessMessages() on a regular basis to get those callbacks dispatched.

In general people should give peerconnection_client a wide berth - figuring out quirks of this buggy, poorly maintained contraption takes too much time imo.

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