Problem getting video-only samples from custom SampleStream

1. Overview

We recently released Media3 DataSource example for our own SLDP low latency streaming protocol. SLDP is a WebSockets-based protocol that we made back in 2017 as a replacement for RTMP which was being discontinued by Adobe at the time. The backend for SLDP protocol is Nimble Streamer, our software media server for video/audio streaming.

We decided to open its source to allow our customers having better adoption via Media3 and opened its implementation as a DataSource: https://github.com/Softvelum/sldp-media3-exo-plugin

We have an issue with video-only mode. Kristina Simakova advised us to post a question here in case there is some solution from Media3 team.

2. Problem Description

Playback is not started if stream is video-only. Both video+audio and audio-only streams work fine.

3. Reproduction

a. Fork sldp-media3-exo-example

b. In ExoScreen.kt disable audio track:

trackSelector.setParameters(
        trackSelector.parameters
            .buildUpon()
            .setDisabledTrackTypes(setOf(C.TRACK_TYPE_AUDIO))
    )

c. First video frame is displayed, but playback is not started.

4. Stream Availability

Test stream URL is wss://demo-nimble.softvelum.com/live/bbb
Same stream using VP8 codec wss://demo-nimble.softvelum.com/live/bbb-360p-25fps-vp8
Same stream via HLS https://demo-nimble.softvelum.com/live/bbb-360p/playlist.m3u8

5. Analysis & Observations

Our understanding of ExoPlayer's behavior in this scenario is as follows:

• a. SldpMediaSource downloads the manifest and returns available tracks via getTrackGroups callback. We use 2 track groups for video and audio.
• b. ExoPlayer picks desired tracks via selectTracks then calls readData method of SldpSampleStream instance.
• c. It appears ExoPlayer in case if single video track is available read first 16 frames and doesn't call readData anymore.

6. Questions for the ExoPlayer Team

What would be the right way to provide video-only samples from SampleStream implementation?

Thank you for your time and assistance.