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• movenc : Ensure no separate moof written for empty track

  12 août 2021, par Hu Weiwen

  movenc : Ensure no separate moof written for empty track
  track->mdat_buf can be not NULL while the track is still empty if the
  
  last packet write failed.
  Signed-off-by : Hu Weiwen <sehuww@mail.scut.edu.cn>
  
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] libavformat/movenc.c

• Convert DTS to AC3 but only if there is no AC3 track already present in container

  24 mars, par Domagoj

  I have sound system that does not support DTS only AC3. I'm automating the process using bash that detects when movie was added to folder, downloads subtitles and converts audio track to AC3 using this command (one part of it) :

  


  ffmpeg -i "{{episode}}" -map 0:v -map 0:a:0 -map 0:a -map 0:s -c:v copy -c:a copy -c:s copy -c:a:0 ac3 -b:a:0 640k "{{directory}}"/{{episode_name}}temp2.mkv

  


  This works without issue and I end up with a .mkv file that contains original DTS audio track and newly created AC3 audio track. The issue is that some files already contain both AC3 and DTS tracks and in those cases I end up with two AC3 tracks and one DTS track. Another issue is that this command is triggered every time there is update to subtitles. So it's possible that the command will execute multiple times in a period of a few days and the container will have X number of the AC3 tracks.

  


  I need a way to detect if file already contains AC3 track before I initiate command from above, but I'm not sure what the command would be. Any help is appreciated !

  


• How to mix audio description track into stereo mix in FFMPEG or SOX

  4 mai 2022, par Overlook Motel

  I have a video file with a stereo mix. I have also been provided with an additional audio description track (a narration which describes what's happening on screen for visually-impaired audiences) as a mono WAV.

  


  I am trying to mix the two together, however the tricky part is adjusting the levels. The levels of the main mix should be dipped before and raised back again after each line of speech in the AD track.

  


  The company who produced the AD track have offered to do this for a fee, however I noticed that their fee is static regardless of the length of the film, so I assume it must be an automated process (if it involved a sound mixer in a studio, it'd be charged at a per minute rate).

  


  I'm wondering if it's possible to do this myself in FFMPEG.

  


  The AD track is cleanly recorded at a consistent level and is entirely silent in between the lines of narration. So imagine it would be in principle possible to determine where the main mix needs to go up and down.

  


  Would probably need to :

  


  

  1. Analyse the levels of the AD track and convert to a list of "fade down here", "fade up here" instructions.

  


  2. Apply that list of instructions to the main mix to create an intermediate.

  


  3. Mix together the intermediate with the AD track.

  


  


  The final step could be achieved with the amix filter, but I have little idea how to approach the first 2 steps.

  


  Does anyone know if this is achievable with FFMPEG ? I'd also be open to using other programs such as SOX.