[v1.16.3] RTSP source with extra Data (Generic) track rejected when `alwaysAvailableTracks` is set

[ranggakd]

Which version are you using?

v1.16.3

Which operating system are you using?

Linux amd64 standard

Describe the issue

Environment

• MediaMTX: v1.16.3
• OS: Ubuntu 20.04
• Source camera RTSP includes: H265 + G711(alaw) + Data(Generic)

Actual behavior

MediaMTX logs:

ERR [path atm-proxy] [RTSP source] wants to publish [H265 G711 Generic], but stream expects [H265 G711]
(and same for other similar cameras)

Expected behavior

When alwaysAvailableTracks lists required media tracks (video/audio), source should still be accepted if it has an additional Generic/Data track, or there should be an option to ignore extra tracks.

Workaround

Removing alwaysAvailableTracks and alwaysAvailable avoids the rejection, but we need alwaysAvailable behavior with declared tracks.

Question

Is strict exact track equality intended here?
If yes, can we get an option like ignoreExtraTracks: true (or wildcard for Generic/Data) in a future version?

Miscellaneous

Path Probing

Probe the path

ffprobe rtsp://localhost:8554/atm-proxy

Giving this result

ffprobe version 4.2.7-0ubuntu0.1 Copyright (c) 2007-2022 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.4.0-1ubuntu1~20.04.1)
  configuration: --prefix=/usr --extra-version=0ubuntu0.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
[rtsp @ 0x55bc4918e980] method SETUP failed: 461 Unsupported Transport
Input #0, rtsp, from 'rtsp://localhost:8554/atm-proxy':
  Metadata:
    title           :  
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: hevc (Main), yuv420p(tv), 1920x1080 [SAR 1:1 DAR 16:9], 30 fps, 30 tbr, 90k tbn, 30 tbc
    Stream #0:1: Audio: pcm_alaw, 8000 Hz, 1 channels, s16, 64 kb/s

Original Source Probing

Probe the original source

ffprobe "rtsp://admin:***@192.168.1.108:554/profile2"

Giving this result

ffprobe version 4.2.7-0ubuntu0.1 Copyright (c) 2007-2022 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.4.0-1ubuntu1~20.04.1)
  configuration: --prefix=/usr --extra-version=0ubuntu0.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
Input #0, rtsp, from 'rtsp://admin:Admin123%23@192.168.1.108:554/profile2':
  Metadata:
    title           : profile2
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: hevc (Main), yuv420p(tv, GBR), 704x576, 10 fps, 25 tbr, 90k tbn, 15 tbc
    Stream #0:1: Audio: pcm_alaw, 8000 Hz, 1 channels, s16, 64 kb/s
    Stream #0:2: Data: none
Unsupported codec with id 0 for input stream 2

Describe how to replicate the issue

Steps to reproduce

1. Run MediaMTX with config below.

2. Confirm source stream tracks:

   ffprobe "rtsp://admin:***@192.168.1.108:554/profile2"

   Output shows:
   Stream #0:0 Video: hevc
   Stream #0:1 Audio: pcm_alaw
   Stream #0:2 Data: none (Generic track)

3. Observe MediaMTX logs.

MediaMTX configuration

paths:
  atm-proxy:
    source: "rtsp://admin:***@192.168.1.108:554/profile2"
    rtspTransport: tcp
    alwaysAvailable: true
    alwaysAvailableTracks:
      - codec: H265
      - codec: G711
        sampleRate: 8000
        channelCount: 1
        muLaw: false

MediaMTX logs

2|media-server | 2026/03/09 13:39:09 ERR [path atm-proxy] [RTSP source] wants to publish [H265 G711 Generic], but stream expects [H265 G711]

Packet dump

No response

[ranggakd]

Thanks for checking this. If you’re open to it, I can prepare a PR for this behaviour (e.g., optional handling of extra Generic/Data tracks while keeping alwaysAvailableTracks constraints). Let me know your preferred approach, and I’ll align with your contribution guidelines.

[aler9]

Hello, the main limitation that you have to work with is that most streaming protocols require track list to be sent once, during the initial handshake. Even protocols that can send track list multiple times (MPEG-TS, SRT and derivated) cannot use dynamic tracks because no player support that.

Therefore, track list must be static and available immediately.

You have to pick an architectural direction before starting any implementation, and there are at least 3:

• improve alwaysAvailableTracks in order to allow defining a "generic" track with the right definition (codec: generic), the problem is that there are several parameters that need to be added and most of them are protocol-specific (rtpMap, mediaType at least for RTSP)

• discard the generic track before feeding the stream to an alwaysAvailable path. This is already possible by using ffmpeg inside runOnReady of another path, using it to read the stream, remove the track and republish the stream to the intended path:

  paths:
    original:
     source: rtsp://...
     runOnReady: ffmpeg -i rtsp://localhost:8554/original -map 0:v:0 -map 0:a:0 -c copy -f rtsp rtsp://localhost:8554/final
  
   final:
     alwaysAvailable: true
     ...

  this does not require any change to the server.

• since using ffmpeg seems like an hack, you can improve the server somehow to perform track discarding natively, without ffmpeg.

Your choice.