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• How does FFmpeg determine the dispositions of an MP4 track ?

  5 mars, par obskyr

  The Issue

  


  FFmpeg has a concept of “dispositions” – a property that describes the purpose of a stream in a media file. For example, here are the streams in a file I have lying around, with the dispositions emphasized :

  


    Stream #0:0[0x1](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo,&#xA;fltp, 251 kb/s <strong><em>(default)</em></strong>&#xA;      Metadata:&#xA;        creation_time   : 2021-11-10T20:14:06.000000Z&#xA;        handler_name    : Core Media Audio&#xA;        vendor_id       : [0][0][0][0]&#xA;&#xA;  Stream #0:1[0x2](und): Video: mjpeg (Baseline) (jpeg / 0x6765706A),&#xA;yuvj420p(pc, bt470bg/unknown/unknown), 1024x1024, 0 kb/s, 0.0006 fps, 3.08 tbr,&#xA;600 tbn <strong><em>(default) (attached pic) (timed thumbnails)</em></strong>&#xA;      Metadata:&#xA;        creation_time   : 2021-11-10T20:14:06.000000Z&#xA;        handler_name    : Core Media Video&#xA;        vendor_id       : [0][0][0][0]&#xA;&#xA;  Stream #0:2[0x3](und): Data: bin_data (text / 0x74786574)&#xA;      Metadata:&#xA;        creation_time   : 2021-11-10T20:14:06.000000Z&#xA;        handler_name    : Core Media Text&#xA;&#xA;  Stream #0:3[0x0]: Video: mjpeg (Baseline), yuvj420p(pc, bt470bg/unknown/&#xA;unknown), 1024x1024 [SAR 144:144 DAR 1:1], 90k tbr, 90k tbn <strong><em>(attached pic)</em></strong>

  


  However, if I make any modification to this file’s chapter markers using the C++ library MP4v2 (even just re-saving the existing ones : auto f = MP4Modify("test.m4a"); MP4Chapter_t* chapterList; uint32_t chapterCount; MP4GetChapters(f, &chapterList, &chapterCount); MP4SetChapters(f, chapterList, chapterCount); MP4Close(f);), some of these dispositions are removed :

  


    Stream #0:0[0x1](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo,&#xA;fltp, 251 kb/s <strong><em>(default)</em></strong>&#xA;      Metadata:&#xA;        creation_time   : 2021-11-10T20:14:06.000000Z&#xA;        handler_name    : Core Media Audio&#xA;        vendor_id       : [0][0][0][0]&#xA;&#xA;  Stream #0:1[0x2](und): Video: mjpeg (Baseline) (jpeg / 0x6765706A),&#xA;yuvj420p(pc, bt470bg/unknown/unknown), 1024x1024, 0 kb/s, 0.0006 fps, 3.08 tbr,&#xA;600 tbn <strong><em>(default)</em></strong> <kbd>← “attached pic” and “timed thumbnails” removed!</kbd>&#xA;      Metadata:&#xA;        creation_time   : 2021-11-10T20:14:06.000000Z&#xA;        handler_name    : Core Media Video&#xA;        vendor_id       : [0][0][0][0]&#xA;&#xA;  Stream #0:2[0x0]: Video: mjpeg (Baseline), yuvj420p(pc, bt470bg/unknown/&#xA;unknown), 1024x1024 [SAR 144:144 DAR 1:1], 90k tbr, 90k tbn <strong><em>(attached pic)</em></strong>&#xA;&#xA;  Stream #0:3[0x4](und): Data: bin_data (text / 0x74786574)&#xA;  <kbd>This stream was moved to the end, but that’s intended behavior. It contains chapter titles, and we just edited the chapters.</kbd>&#xA;      Metadata:&#xA;        creation_time   : 2025-03-05T09:56:31.000000Z

  


  It also renders the file unplayable in MPC-HC (but not in VLC !), which is apparently a bug in MP4v2. I’m currently investigating that bug to report and potentially fix it, but that’s a separate issue – in my journey there, I’m wracking my brain trying to understand what it is that MP4v2 changes to make FFmpeg stop reporting the “attached pic” and “timed thumbnails” dispositions. I’ve explored the before-and-afters in MP4 Box, and I can’t for the life of me find which atom it is that differs in a relevant way.

  


  (I’d love to share the files, but unfortunately the contents are under copyright – if anyone knows of a way to remove the audio from an MP4 file without changing anything else, let me know and I’ll upload dummied-out versions. Without them, I can’t really ask about the issue directly. I can at least show you the files’ respective atom trees, but I’m not sure how relevant that is.)

  


  The Question

  


  I thought I’d read FFmpeg’s source code to find out how it determines dispositions for MP4 streams, but of course, FFmpeg is very complex. Could someone who’s more familiar with C and/or FFmpeg’s codebase help me sleuth out how FFmpeg determines dispositions for MP4 files (in particular, “attached pic” and “timed thumbnails”) ?

  


  Some Thoughts…

  


  

  • I figure searching for “attached_pic” might be a good start ?

  


  • Could the MP4 muxer movenc.c be helpful ?

  


  • I’d imagine what we’d really like to look at is the MP4 demuxing process, as it’s during demuxing that FFmpeg determines dispositions from the data in the file. After poring over the code for hours, however, I’ve been utterly unable to find where that happens.

  


  


• FFmpeg matlab error : At least one output file must be specified ? [closed]

  3 mars, par as moh

  I'm trying to get I frames from a video using Matlab using this command system(sprintf('ffmpeg -i testVid.mp4 -vf "select=eq(pict_type\,I)" -vsync vfr output_%03d.png')); ,but i get this message

  


   ffmpeg version 7.1-full_build-www.gyan.dev Copyright (c) 2000-2024 the FFmpeg developers 
  built with gcc 14.2.0 (Rev1, Built by MSYS2 project) 
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libaribb24 --enable-libaribcaption --enable-libdav1d --enable-libdavs2 --enable-libopenjpeg --enable-libquirc --enable-libuavs3d --enable-libxevd --enable-libzvbi --enable-libqrencode --enable-librav1e --enable-libsvtav1 --enable-libvvenc --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxeve --enable-libxvid --enable-libaom --enable-libjxl --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-dxva2 --enable-d3d11va --enable-d3d12va --enable-ffnvcodec --enable-libvpl --enable-nvdec --enable-nvenc --enable-vaapi --enable-libshaderc --enable-vulkan --enable-libplacebo --enable-opencl --enable-libcdio --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora --enable-libtwolame --enable-libvo-amrwbenc --enable-libcodec2 --enable-libilbc --enable-libgsm --enable-liblc3 --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint 
  libavutil      59. 39.100 / 59. 39.100 
  libavcodec     61. 19.100 / 61. 19.100 
  libavformat    61.  7.100 / 61.  7.100 
  libavdevice    61.  3.100 / 61.  3.100 
  libavfilter    10.  4.100 / 10.  4.100 
  libswscale      8.  3.100 /  8.  3.100 
  libswresample   5.  3.100 /  5.  3.100 
  libpostproc    58.  3.100 / 58.  3.100 
Trailing option(s) found in the command: may be ignored. 
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'testVid.mp4': 
  Metadata: 
    major_brand     : isom 
    minor_version   : 512 
    compatible_brands: isomiso2avc1mp41 
    encoder         : Lavf57.83.100 
  Duration: 00:00:02.02, start: 0.000000, bitrate: 12798 kb/s 
  Stream #0:0[0x1](eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuvj420p(pc, progressive), 1280x720 [SAR 1:1 DAR 16:9], 12662 kb/s, 29.74 fps, 30 tbr, 90k tbn (default) 
      Metadata: 
        handler_name    : VideoHandler 
        vendor_id       : [0][0][0][0] 
  Stream #0:1[0x2](eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 121 kb/s (default) 
      Metadata: 
        handler_name    : SoundHandler 
        vendor_id       : [0][0][0][0] 
At least one output file must be specified 


  


  i searched and tried many cases but i don't know where is the problem, any help please ?

  


• ffmpeg Non monotonous DTS, Previous DTS is always the same, audio microphone streaming [closed]

  5 février, par adrien gonzalez

  I'm using ffmpeg to stream audio from a microphone using rtp. I'm on Raspberry and use an external sound card (HifiBerry DAC + ADC Pro).
My goal is to stream audio with the lowest latency possible to others Raspberry reading this audio with ffplay. I try not to compress the audio flux and leave it untouched as wav 48000 Hz.
I encounter often some Non Monotonous DTS errors. When this happens I have a latency of hundred of milliseconds adding itself.
I tried to add the +igndts flag but it is not changing anything. Also tried +genpts flag.

  


  What is weird is that the previous DTS is always the same (201165 is the example below) and does not seems to change.
I looked on forums for answers but I'm unable to find one.

  


  Here is my bash command :

  


  ffmpeg -guess_layout_max 0 -re -f alsa -i hw -acodec pcm_s16le -ac 1 -payload_type 10 -f rtp rtp://192.168.1.152:5003

  


  And the result from the terminal :

  


  ffmpeg version 5.1.6-0+deb12u1+rpt1 Copyright (c) 2000-2024 the FFmpeg developers


built with gcc 12 (Debian 12.2.0-14)
  configuration: --prefix=/usr --extra-version=0+deb12u1+rpt1 --toolchain=hardened --incdir=/usr/include/aarch64-linux-gnu --enable-gpl --disable-stripping --disable-mmal --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libglslang --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librabbitmq --enable-librist --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libssh --enable-libsvtav1 --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sand --enable-sdl2 --disable-sndio --enable-libjxl --enable-neon --enable-v4l2-request --enable-libudev --enable-epoxy --libdir=/usr/lib/aarch64-linux-gnu --arch=arm64 --enable-pocketsphinx --enable-librsvg --enable-libdc1394 --enable-libdrm --enable-vout-drm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-libplacebo --enable-librav1e --enable-shared
  libavutil      57. 28.100 / 57. 28.100
  libavcodec     59. 37.100 / 59. 37.100
  libavformat    59. 27.100 / 59. 27.100
  libavdevice    59.  7.100 / 59.  7.100
  libavfilter     8. 44.100 /  8. 44.100
  libswscale      6.  7.100 /  6.  7.100
  libswresample   4.  7.100 /  4.  7.100
  libpostproc    56.  6.100 / 56.  6.100
Input #0, alsa, from 'hw':
  Duration: N/A, start: 1738663653.066577, bitrate: 1536 kb/s
  Stream #0:0: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
Output #0, rtp, to 'rtp://192.168.1.152:5003':
  Metadata:
    encoder         : Lavf59.27.100
  Stream #0:0: Audio: pcm_s16le, 48000 Hz, mono, s16, 768 kb/s
    Metadata:
      encoder         : Lavc59.37.100 pcm_s16le
SDP:
v=0
o=- 0 0 IN IP4 127.0.0.1
s=No Name
c=IN IP4 192.168.1.152
t=0 0
a=tool:libavformat LIBAVFORMAT_VERSION
m=audio 5003 RTP/AVP 10
b=AS:768

[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201160; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201155; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201149; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201142; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201134; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201124; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201114; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201102; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201089; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201075; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201060; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201044; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201027; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 201009; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 200990; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 200970; changing to 201165. This may result in incorrect timestamps in the output file.
[rtp @ 0x558b48ea90] Non-monotonous DTS in output stream 0:0; previous: 201165, current: 200949; changing to 201165. This may result in incorrect timestamps in the output file.


  


  I tried to add the +igndts flag but it is not changing anything. Also tried +genpts flag. I expected the DTS to restore itself but I still have the same issue