[bug] Track from video publication is always null

[pitazzo]

Describe the bug
Since plugin's version 2.5.1, on any participant event, when checking any videoTrackPublications, the property .track is always null. The issue happens, at least, in Android devices. I suspect that #867 does not take into consideration some edge case, causing the issue. Also, no TrackSubscribedEvent being fired.

To Reproduce

1. Build example app from repo clone for Android
2. Connect to a given room
3. Connect to same room with web demo
4. In the web demo, the remote video track is visible, while in the Android version, the no video widget is displayed for the remote participant. Audio track works as expected.

Expected behavior
Remote's video track should be non null at some point so VideoRenderer can be created,

Platform information

• Flutter version: Flutter (Channel stable, 3.32.8, on macOS 15.6.1 24G90 darwin-arm64, locale es-ES)
• Plugin version: 2.5.3, but this was introduced at 2.5.1
• Flutter target OS: Android physical device
• Flutter target OS version: Android 15

[hiroshihorie]

Hi @pitazzo I think this PR is related #924
.track property should not be nil by the time of a TrackSubscribedEvent. It will still be nil at TrackPublishedEvent.

[pitazzo]

hi @hiroshihorie thanks for having a look on this.

We've just built our app with the content of your branch hiroshi/fix-subscribed-event and the issue is still happening. No TrackSubscribedEvent is being emitted in our app. Here's a trace of the events that we're registering. For reference, remote participant is already in the room when joining.

I/flutter (10955): │ 💬 Just received a ParticipantPermissionsUpdatedEvent 
I/flutter (10955): │ 💬 Just received a ParticipantStateUpdatedEvent 
I/flutter (10955): │ 💬 Just received a ParticipantPermissionsUpdatedEvent 
I/flutter (10955): │ 💬 Just received a LocalTrackPublishedEvent 
I/flutter (10955): │ 💬 Just received a ParticipantStateUpdatedEvent 
I/flutter (10955): │ 💬 Just received a RoomConnectedEvent 
I/flutter (10955): │ 💬 Just received a LocalTrackSubscribedEvent 
I/flutter (10955): │ 💬 Just received a ParticipantPermissionsUpdatedEvent 
I/flutter (10955): │ 💬 Just received a LocalTrackSubscribedEvent 
I/flutter (10955): │ 💬 Just received a RoomMetadataChangedEvent 
I/flutter (10955): │ 💬 Just received a ParticipantConnectionQualityUpdatedEvent 
I/flutter (10955): │ 💬 Just received a ParticipantConnectionQualityUpdatedEvent 
I/flutter (10955): │ 💬 Just received a LocalTrackUnpublishedEvent 
I/flutter (10955): │ 💬 Just received a LocalTrackUnpublishedEvent 
I/flutter (10955): │ 💬 Just received a RoomDisconnectedEvent 

Currently, we try to get the remote video track on ParticipantConnectedEvent, TrackSubscribedEvent and right after connection of the local participant. We're not sure of this being the most correct practice, but till 2.5.0+hotfix.3 it worked just fine

[hiroshihorie]

@pitazzo Can you reproduce with iOS ? I can't reproduce with iOS, TrackSubscribedEvent works as expected. I will proceed to investigate with Android.

[pitazzo]

@hiroshihorie I just tried with an iOS device and I can confirm that it didn't happen. Thus, bug appears to be limited to Android devices. However, please note that our flow is not exactly the same in the iOS app and the Android app, as because of our use case Android devices always connect after.

[hiroshihorie]

@pitazzo I can't reproduce it with Android simulator also, can you reproduce 100% ? Any other hints to reproduce it ?

[MarcusHellkvist]

We are also experiencing this issue but we have the reverse where its almost always a problem with iOS and never with Android (we have some reported cases). But this is not only related to the Livekit SDK because everything was working fine until we updated our iOS test devices to a never iOS version.

We made the jump from livekit_client: 2.3.2 to livekit_client: 2.5.1 in order to fix the android 16kb support thing. At this time, everything was working fine with the remote participants track on older iOS devices. But then we got a lot of reports about people not seeing each other in the calls. We update our iOS devices to newer versions and the issue has been able to be replicated ever since.

The funny thing is; if you connect with either your camera or microphone track as null it fixes the problem!

Future<FastConnectOptions> getOptions() async {
    if (lkPlatformIs(PlatformType.iOS)) {
      await localAudioTrack?.dispose();
      localAudioTrack = null;
    }
    return FastConnectOptions(
      camera: TrackOption(
        track: localVideoTrack,
        enabled: localVideoTrack?.mediaStreamTrack.enabled,
      ),
      microphone: TrackOption(
        track: localAudioTrack,
        enabled: localAudioTrack?.mediaStreamTrack.enabled,
      ),
    );
  }

On iPhone 12 running iOS 18.7.1 with Livekit SDK 2.5.1 and forward - remote participants tracks are null upon joining as a local participant.

[hiroshihorie]

Can you try #928 it could be related.

[pitazzo]

hi @hiroshihorie
I tried our different use cases with #928 and problem seems to be resolved. However, IMHO, makes sense that it's some kind of unhandled race condition, as after some more testing with the 2.5.3 version, issue was underterministc; sometimes happened and sometimes didn't. With #928 , seems to be consistent.

[hiroshihorie]

@pitazzo Yes #928 Fixes a race condition, I think introduced by recent "async improvements". I think I'll merge & ship this fix. Thank you for testing.

[hiroshihorie]

@pitazzo Can you try v2.5.4 ? Thank you.

[pitazzo]

hi @hiroshihorie after some initial testing, issue seems to be resolved! thanks a lot for your efforts!

[hiroshihorie]

I'm glad it's resolved, thanks for testing 🙂