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• How does FFmpeg determine the “attached pic” and “timed thumbnails” dispositions of an MP4 track ?

  6 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.

  


  


• 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 with PHP-7.0 on Ubuntu

  25 octobre 2018, par Gabriel Bueno Lemes da Silva

  I have a NGINX server with PHP-7.0 and I would like to install the ffmpeg-php extension. I’ve been trying for a few days now and in many ways.

  The method that worked so far was compiling ffmpeg (https://ffmpeg.org/releases/ffmpeg-4.0.2.tar.bz2) manually, but when trying to compile ffmpeg-php (https: // sourceforge. net / projects / ffmpeg-php / files / ffmpeg-php / 0.6.0 / ffmpeg-php-0.6.0.tbz2 / download) I am encountering the following error message :

  root@zumbiserver-mercury : /php7-ffmpeg# make /bin/bash

  /root/php7-ffmpeg/libtool —mode=compile cc -I. -I/root/php7-ffmpeg
  -DPHP_ATOM_INC -I/root/php7-ffmpeg/include -I/root/php7-ffmpeg/main -I/root/php7-ffmpeg -I/usr/include/php/20151012 -I/usr/include/php/20151012/main -I/usr/include/php/20151012/TSRM -I/usr/include/php/20151012/Zend -I/usr/include/php/20151012/ext -I/usr/include/php/20151012/ext/date/lib -I/usr/local/include/libavcodec/ -I/usr/local/include/libavformat/ -I/usr/local/include/libavutil/ -I/usr/local/include/libswscale/ -I/usr/local/include/libavfilter/ -I/usr/local/include/libavdevice/ -DHAVE_CONFIG_H -g -O2 -Wall -fno-strict-aliasing -c /root/php7-ffmpeg/ffmpeg-php.c -o ffmpeg-php.lo libtool : compile : cc
  -I. -I/root/php7-ffmpeg -DPHP_ATOM_INC -I/root/php7-ffmpeg/include -I/root/php7-ffmpeg/main -I/root/php7-ffmpeg -I/usr/include/php/20151012 -I/usr/include/php/20151012/main -I/usr/include/php/20151012/TSRM -I/usr/include/php/20151012/Zend -I/usr/include/php/20151012/ext -I/usr/include/php/20151012/ext/date/lib -I/usr/local/include/libavcodec/ -I/usr/local/include/libavformat/ -I/usr/local/include/libavutil/ -I/usr/local/include/libswscale/ -I/usr/local/include/libavfilter/ -I/usr/local/include/libavdevice/ -DHAVE_CONFIG_H -g -O2 -Wall -fno-strict-aliasing -c /root/php7-ffmpeg/ffmpeg-php.c -fPIC -DPIC -o .libs/ffmpeg-php.o In
  file included from /usr/include/x86_64-linux-gnu/sys/stat.h:104:0,
  from /usr/include/php/20151012/Zend/zend_stream.h:28,
  from /usr/include/php/20151012/Zend/zend.h:41,
  from /usr/include/php/20151012/main/php.h:36,
  from /root/php7-ffmpeg/ffmpeg-php.c:40 : /usr/include/x86_64-linux-gnu/bits/stat.h:91:21 : error : field
  ‘st_atim’ has incomplete type
  struct timespec st_atim ; /* Time of last access. /
  ^ /usr/include/x86_64-linux-gnu/bits/stat.h:92:21 : error : field
  ‘st_mtim’ has incomplete type
  struct timespec st_mtim ; / Time of last modification. /
  ^ /usr/include/x86_64-linux-gnu/bits/stat.h:93:21 : error : field
  ‘st_ctim’ has incomplete type
  struct timespec st_ctim ; / Time of last status change. /
  ^ /usr/include/x86_64-linux-gnu/bits/stat.h:152:21 : error : field
  ‘st_atim’ has incomplete type
  struct timespec st_atim ; / Time of last access. /
  ^ /usr/include/x86_64-linux-gnu/bits/stat.h:153:21 : error : field
  ‘st_mtim’ has incomplete type
  struct timespec st_mtim ; / Time of last modification. /
  ^ /usr/include/x86_64-linux-gnu/bits/stat.h:154:21 : error : field
  ‘st_ctim’ has incomplete type
  struct timespec st_ctim ; / Time of last status change. /
  ^ In file included from /usr/include/php/20151012/Zend/zend_stream.h:28:0,
  from /usr/include/php/20151012/Zend/zend.h:41,
  from /usr/include/php/20151012/main/php.h:36,
  from /root/php7-ffmpeg/ffmpeg-php.c:40 : /usr/include/x86_64-linux-gnu/sys/stat.h:364:31 : error : array type has
  incomplete element type ‘struct timespec’
  const struct timespec __times[2],
  ^ /usr/include/x86_64-linux-gnu/sys/stat.h:371:54 : error : array type has
  incomplete element type ‘struct timespec’ extern int futimens (int
  __fd, const struct timespec __times[2]) __THROW ;
  ^ In file included from /usr/include/php/20151012/main/php.h:395:0,
  from /root/php7-ffmpeg/ffmpeg-php.c:40 : /usr/include/php/20151012/Zend/zend_virtual_cwd.h:218:2 : error :
  unknown type name ‘time_t’ time_t expires ;
  ^ /usr/include/php/20151012/Zend/zend_virtual_cwd.h:248:86 : error :
  unknown type name ‘time_t’ CWD_API realpath_cache_bucket
  realpath_cache_lookup(const char *path, int path_len, time_t t) ;
  ^ /root/php7-ffmpeg/ffmpeg-php.c : In function ‘zm_startup_ffmpeg’ :
  /root/php7-ffmpeg/ffmpeg-php.c:108:5 : warning : implicit declaration of
  function ‘avcodec_init’ [-Wimplicit-function-declaration]
  avcodec_init() ;
  ^ /root/php7-ffmpeg/ffmpeg-php.c:111:5 : warning : ‘av_register_all’ is deprecated [-Wdeprecated-declarations]
  av_register_all() ;
  ^ In file included from /root/php7-ffmpeg/ffmpeg-php.c:43:0 : /usr/local/include/libavformat/avformat.h:2025:6 : note : declared here
  void av_register_all(void) ;

    ^ Makefile:194: recipe for target 'ffmpeg-php.lo' failed make: *** [ffmpeg-php.lo] Error 1

  Can someone give me a light ? I do not know what else to do !