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• FFMPEG : Converting chapter points when converting PAL to NTSC

  26 février 2020, par koberulz

  I have a batch file converting my PAL TV series DVDs to the correct NTSC frame rates :

  for %%F in (*.mkv) do (
  
  echo A = LWLibAvVideoSource("%%F"^) > script.avs
  
  echo B = LWLibAvAudioSource("%%F"^) >> script.avs
  
  echo AudioDub(A,B^) >> script.avs
  
  echo AssumeFPS(24000,1001,sync_audio=true^) >> script.avs
  
  echo ResampleAudio(48000^) >> script.avs
  
  ffmpeg\ffmpeg.exe -i script.avs -aspect 16:9 -acodec ac3 -vcodec libx264 -preset slow -qp 16 "Output\%%F"
  
  del "%%F.lwi"
  
  del script.avs
  
  )
  
  
  
  pause

  But this removes the chapter points. I’m assuming map_chapters, if I figured out how to use it, would just shift in the chapters at the old PAL timestamps, so they wouldn’t match up to the correct times in the actual NTSC video ? Is there a way to get the chapters in the right spots other than manually opening each episode, finding the equivalent points, and manually creating each chapter ?

• FMP4 moof box sequence number ordering

  15 avril 2024, par Daniel

  I wanted to do a basic fragmented mp4 broadcast program with avformat libs and HTML5 video and MSE.

  



  This is a live stream and I use avformat to copy h264 data to mp4 fragments.

  



  Here is my basic drawing of clients attaching to the stream :

  



  

  



  So, with words :

  



  

  1. C1J : First Client joins :


     

     • avformat process starts

     


     • ftyp, moov, moof, mdat boxes will be served to Client1

     


     • ftyp and moov atoms are both saved for later reuse

     


  


  2. C2J : Second Client joins (later in time) :


     

     • avformat process is ongoing (because it is still serving moof and mdat boxes for Client1)

     


     • previously saved ftyp and moov boxes will be served first to Client2

     


     • after ftyp and moov boxes were served, Client2 will join to the stream at the next moof box.

     


  


  



  I have saved an mp4 file to disk from both clients.

  



  Atoms' order within both files looks good : ftype, moov, moof, mdat, moof, mdat...

  



  Both files can be played by media players (like VLC) and also in browsers directly (Opera).

  



  Client1 can be played also via MSE in the browser (Opera), but Client2's stream is not displaying with MSE (Opera).

  



  No errors on the JS console, and media-internals looks also good (at least equivalent with Client1's one).

  



  Now I realized that every moof box contains an mfhd box (header) with a sequenceNumber field.

  



  Of course in Client1's first moof box this sequenceNumber is 1.
However in the later joined Client2's first moof box this sequenceNumber is always >= 1 (in my case it is 16).

  



  What do I need to modify in the moof boxes in Client2 to have a valid fmp4 from the beginning ?

  



  I think Opera's HTML5 video does not like if sequenceNumber does not start from 1, but there shall be other requirements for being it valid.

  


• FFMPEG : add more tracks to previous amix output

  13 avril 2020, par Daniel Rothig

  I can mix multiple audio tracks in ffmpeg with a command like

  



  ffmpeg -i track1.wav \
       -i track2.wav \
       -i track3.wav \
       -filter_complex "[0:a] [1:a] [2:a] amix=3 [out]" \
       -map "[out]" \
       -c copy mix.wav


  



  All tracks are the same length in my use-case. Periodically, I'll receive a new track (call it track4.wav) and I would like to produce a new mix of all four tracks. The naive solution would be to re-run the above comment with with the additional track, but this becomes expensive as the number of tracks gets large.

  



  Is there an elegant way to combine mix.wav and track4.wav to get the equivalent result, without an imbalance in volume levels or significant loss of quality compared to the "naive" approach ?