SRT setOnlyVideo(true) Still Sends Audio Track in PSI Tables

[Piyoxz]

When using setOnlyVideo(true) for SRT streaming, the MPEG-TS muxer still includes audio track information in PSI tables (PAT/PMT).

As a result, downstream servers (e.g. ZLMediaKit) detect and expect an audio track even though no audio packets are actually sent.

Impact

This behavior causes several issues on strict TS demuxers:

• ❌ Phantom audio track detected (e.g. mpeg4-generic)
• ❌ Potential TS demuxer crashes when audio packets never arrive
• ❌ Incorrect stream metadata reported by server APIs

Expected Behavior

When setOnlyVideo(true) is called before startStream():

• ✅ PSI tables (PAT/PMT) contain only video track
• ✅ No audio PID registered in PMT
• ✅ Server receives pure video-only metadata
• ✅ No audio packets sent (this already works correctly)

Actual Behavior

• ✅ SrtClient.setOnlyVideo(true) correctly sets commandsManager.audioDisabled = true
• ✅ SrtSender.getMpegTsPackets() correctly skips audio packets
• ❌ Audio track is still registered in PSI tables

Root Cause

In SrtSender.kt:

private fun setTrackConfig(videoEnabled: Boolean, audioEnabled: Boolean) {
  Pid.reset()
  service.clearTracks()
  if (audioEnabled) service.addTrack(commandsManager.audioCodec.toCodec()) // ❌ Audio always added
  if (videoEnabled) service.addTrack(commandsManager.videoCodec.toCodec())
  service.generatePmt()
  psiManager.updateService(service)
}

• audioEnabled is derived from !commandsManager.audioDisabled
• However, this method does not respect setOnlyVideo(true)
• As a result, audio track metadata is added even when audio is explicitly disabled

Server Detection Example (ZLMediaKit)
/index/api/getMediaList response:

{
  "tracks": [
    {
      "codec_id": 2,
      "codec_id_name": "mpeg4-generic", // ❌ Phantom audio track
      "codec_type": 1,
      "channels": 1,
      "sample_rate": 8000
    },
    {
      "codec_id": 1,
      "codec_id_name": "H265",
      "codec_type": 0,
      "width": 1280,
      "height": 720
    }
  ]
}

Steps to Reproduce

1. Prepare video encoder (H265) + audio encoder (AAC)
2. Call srtClient.setOnlyVideo(true)
3. Start streaming:
   startStream("srt://server:9000?streamid=...")
4. Query server metadata (e.g. ZLMediaKit API)
5. Observe: Both audio and video tracks detected

Proposed Fix

Modify SrtSender.setTrackConfig() to respect commandsManager.audioDisabled:

private fun setTrackConfig(videoEnabled: Boolean, audioEnabled: Boolean) {
  Pid.reset()
  service.clearTracks()

  // Only add audio track if enabled AND not explicitly disabled
  if (audioEnabled && !commandsManager.audioDisabled) {
    service.addTrack(commandsManager.audioCodec.toCodec())
  }

  if (videoEnabled) {
    service.addTrack(commandsManager.videoCodec.toCodec())
  }

  service.generatePmt()
  psiManager.updateService(service)

  Log.i(TAG, "Track config: video=$videoEnabled, audio=${audioEnabled && !commandsManager.audioDisabled}")
}

Workaround

Currently using a local patch to force video-only PSI tables:

private fun setTrackConfig(videoEnabled: Boolean, audioEnabled: Boolean) {
  Pid.reset()
  service.clearTracks()
  if (videoEnabled) service.addTrack(commandsManager.videoCodec.toCodec())
  service.generatePmt()
  psiManager.updateService(service)
  Log.i(TAG, "Track config: video=$videoEnabled, audio=false (forced)")
}

Environment

Library Version: rootProject-SNAPSHOT (latest master)

Android: 13 (API 33)

Video Codec: H265

Audio Codec: AAC

Protocol: SRT

Server: ZLMediaKit (2024)

Related Code

srt/src/main/java/com/pedro/srt/srt/SrtSender.kt (line 69–76, 113)

srt/src/main/java/com/pedro/srt/srt/SrtClient.kt (line 163)

srt/src/main/java/com/pedro/srt/srt/CommandsManager.kt (line 55)

[pedroSG94]

Hello,

I tested this case and audio codec is not send in pmt packets

Are you sure that you called it before startStream method?

  val genericStream: GenericStream by lazy {
    GenericStream(requireContext(), this).apply {
      getGlInterface().autoHandleOrientation = true
      getStreamClient().setOnlyVideo(true)
    }
  }

Please check it, meanwhile I will try install your server and test it (it has a free version to test, right?)

[Piyoxz]

Hello,

I tested this case and audio codec is not send in pmt packets

Are you sure that you called it before startStream method?

val genericStream: GenericStream by lazy {
GenericStream(requireContext(), this).apply {
getGlInterface().autoHandleOrientation = true
getStreamClient().setOnlyVideo(true)
}
}
Please check it, meanwhile I will try install your server and test it (it has a free version to test, right?)

Hello,

Thanks for checking

Yes — I’m calling setOnlyVideo(true) before startStream() (inside the GenericStream initialization, before any prepare/start call). However, on my side the audio pipeline still seems to start.

Even with getStreamClient().setOnlyVideo(true), the stream crashes with:

IllegalStateException: AudioEncoder not prepared yet. You must call prepare method before start it

So it looks like an AudioTrack/AudioEncoder is still being started internally even in “only video” mode, and since I’m not preparing audio (because it should be video-only), it throws the exception.

Could you please confirm:

Is setOnlyVideo(true) supposed to completely skip starting audio (encoder + track + TS PMT audio)?

If yes, is there any additional call required to fully disable audio for GenericStream (e.g. disableAudio / setAudioTrack(false), etc.)?

Or is this a known issue in the current version?

Thanks!

[pedroSG94]

Hello,

Yes, prepareAudio is necessary because it could be needed for others reasons. AudioEncoder is always created but it is not the case with the audio source (microphone for example) because you can use NoAudioSource to avoid initialize the microphone.

You need create the AudioEncoder because change the audio source on fly is possible. Also, you can disable audio from the stream but record the audio with startRecord and vice versa.
When you remove the audio track in the stream the audio should be removed from the PMT packet (at least, I tested it and only AVC codec is send to the server).

Can you tell me the way you tested that audio track is send using SRT after disable it and where is the error? PMT packet seems totally fine so maybe the fail is in other thing. I'm no able to check it