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• mov : Do not allow updating the time scale after it has been set

  15 juillet 2013, par Martin Storsjö

  mov : Do not allow updating the time scale after it has been set
  The time scale is set in mdhd, and later validated in the
  
  enclosing trak atom once all of its children have been parsed.
  A loose mdhd atom outside of a trak atom could update the time
  
  scale of the last stream without any validation.
  Reported-by : Mateusz "j00ru" Jurczyk and Gynvael Coldwind
  
  Cc : libav-stable@libav.org
  
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavformat/mov.c

• I don't know the time unit to use for av_dict_set to set a timeout

  9 juin 2020, par ICYMYM

  I am confused. I am using the av_dict_set function to set a time-out, but when I searched for information about av_dict_set, the time unit seems to be different. I don't know how to set it now. Can anyone help ?

  



  I found some code like the following :

  



  pFormatCtx = avformat_alloc_context();

av_dict_set(&opts, "rtsp_transport", "tcp", 0);
//av_dict_set(&opts, "timeout", "5000000", 0);
if(strncmp(stream_url, "rtmp:", sizeof("rtmp:")) == 0){
    av_dict_set(&opts, "timeout", "6", 0); // in secs
}
else if(strncmp(stream_url, "http:", sizeof("http:")) == 0){
    av_dict_set(&opts, "timeout", "6000", 0); // in ms
}

if(avformat_open_input(&pFormatCtx, stream_url, NULL, &opts)!=0)
{
  return 1;
}


  



  Maybe it should set the time unit according to the different protocols (http or rtsp).

  



  Is the code above right ?

  


• FFmpeg concat demuxer negative start time

  6 février 2021, par modfun

  Problem

  


  When using FFmpeg concat demuxer with the -c:v copy option, the initial start time is negative, introducing a black frame for around 0.02 seconds. The video then plays with no other problems. Another question was asked here without any answers.

  


  The black frame appears in Quicktime but not VLC.

  


  Input

  


  The command below shows the start time is at -0.023220, not 0.0

  


  ffmpeg -f concat -safe 0 -i moments.txt -c:v copy combined.mp4
ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with Apple clang version 12.0.0 (clang-1200.0.32.28)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.1_9 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
Input #0, concat, from 'moments.txt':
  Duration: N/A, start: -0.023220, bitrate: 1067 kb/s
    Stream #0:0(und): Video: hevc (Main) (hvc1 / 0x31637668), yuv420p(tv, progressive), 720x1280, 836 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 29.97 tbc
    Metadata:
      handler_name    : Core Media Video
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 230 kb/s
    Metadata:
      handler_name    : Core Media Audio
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
Output #0, mp4, to 'combined.mp4':
  Metadata:
    encoder         : Lavf58.45.100
    Stream #0:0(und): Video: hevc (Main) (hvc1 / 0x31637668), yuv420p(tv, progressive), 720x1280, q=2-31, 836 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 30k tbc
    Metadata:
      handler_name    : Core Media Video
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s
    Metadata:
      handler_name    : Core Media Audio
      encoder         : Lavc58.91.100 aac
frame=  318 fps=0.0 q=-1.0 Lsize=    2208kB time=00:00:10.70 bitrate=1689.9kbits/s speed=72.1x
video:2026kB audio:168kB subtitle:0kB other streams:0kB global headers:2kB muxing overhead: 0.673558%
[aac @ 0x7fd530866a00] Qavg: 472.463



  


  Observations

  


  The negative start time does not occur if I encode the video rather than copy it but encoding takes significantly more time.

  


  Thanks for the help !