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• mkv file out of sync with linear drift

  13 avril 2019, par Zanfronio

  I have a bunch of mkv files, with FLAC as the audio codec and FFV1 as the video one.

  The files were created using an EasyCap aquisition dongle from a VCR analog source. Specifically, I used VLC’s "open acquisition device" prompt and selected PAL. Then, I converted the files (audio PCM, video raw YUV) to (FLAC, FFV1) using

  ffmpeg.exe -i input.avi -acodec flac -vcodec ffv1 -level 3 -threads 4 -coder 1 -context 1 -g 1 -slices 24 -slicecrc 1 output.mkv

  Now, the files are progressively out of sync. It may be due to the fact that while (maybe) the video has a constant framerate, the FLAC track has variable framerate. So, is there a way to sync the track to audio, or something alike ? Can FFmpeg do this ? Thanks

  EDIT

  On Mulvya hint, I plotted the difference in sync at various times ; the first column shows the seconds elapsed, the second shows the difference - in secs. The plot seems to behave linearly, with 0.0078 as a constant slope. NOTE : measurements taken by hands, by means of a chronometer

  

  EDIT 2

  Playing around with VirtualDub, I found that changing the framerate to 25 fps from the original 24.889 (Video->Frame rate...->Change frame rate to) and using the track converted to wav definitely does work. Two problems, though : VirtualDub crashes when importing the original FFV1-FLAC mkv file, so I had to convert the video to H264 to try it out ; more, I find it difficult to use an external encoder to save VirtualDub output.

  So, could I avoid using VirtualDub, and simply use ffmpeg for it ? Here’s the exported vdscript :

      VirtualDub.audio.SetSource("E:\\Cassette\\Filmini\\masters\\Cassetta 4_track2_ita.wav", "");
  
      VirtualDub.audio.SetMode(0);
  
      VirtualDub.audio.SetInterleave(1,500,1,0,0);
  
      VirtualDub.audio.SetClipMode(1,1);
  
      VirtualDub.audio.SetEditMode(1);
  
      VirtualDub.audio.SetConversion(0,0,0,0,0);
  
      VirtualDub.audio.SetVolume();
  
      VirtualDub.audio.SetCompression();
  
      VirtualDub.audio.EnableFilterGraph(0);
  
      VirtualDub.video.SetInputFormat(0);
  
      VirtualDub.video.SetOutputFormat(7);
  
      VirtualDub.video.SetMode(3);
  
      VirtualDub.video.SetSmartRendering(0);
  
      VirtualDub.video.SetPreserveEmptyFrames(0);
  
      VirtualDub.video.SetFrameRate2(25,1,1);
  
      VirtualDub.video.SetIVTC(0, 0, 0, 0);
  
      VirtualDub.video.SetCompression();
  
      VirtualDub.video.filters.Clear();
  
      VirtualDub.audio.filters.Clear();

  The first line imports the wav-converted audio track.
  Can I set an equivalent pipe in ffmpeg (possibly, using FLAC - not wav) ? SetFrameRate2 is maybe the key, here.

• cbs_h264 : Actually decompose end-of-sequence NAL units

  16 octobre 2018, par Mark Thompson

  cbs_h264 : Actually decompose end-of-sequence NAL units
  64c50c0e978cd556dc2da238dfe0bb367e7c1ab9 declared support for decomposing
  
  them but omitted to implement it ; this adds an implementation.
  Also do the same for end-of-stream NAL units, since they are equivalent.
  

  • [DH] libavcodec/cbs_h2645.c
  • [DH] libavcodec/cbs_h264_syntax_template.c

• avformat/libsrt : add several options supported in srt 1.3.0

  23 octobre 2018, par Matsuzawa Tomohiro

  avformat/libsrt : add several options supported in srt 1.3.0
  Several SRT options are missing. Since pkg_config requires libsrt v1.3.0 and above, it should be able to support options added in libsrt v1.3.0 and below.
  
  This commit adds 8 SRT options.
  
  sndbuf, rcvbuf, lossmaxttl, minversion, streamid, smoother, messageapi and transtype
  
  The keys of option are equivalent to stransmit.
  
  https://github.com/Haivision/srt/blob/v1.3.0/apps/socketoptions.hpp#L196-L223
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] doc/protocols.texi
  • [DH] libavformat/libsrt.c
  • [DH] libavformat/version.h