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• Merging audio channels by FFmpeg libraries C++

  13 juin 2023, par Elija

  C/C++ project. There are several audio tracks with an individual number of channels. Each is processed using a avresampler. The avresampler converts all tracks to the same format. At the output of the avresampler, we get a set of channels from all audio tracks. Do the FFmpeg libraries have any standard means to merge all these audio channels into another set of audio channels using AVFrame::ch_layout to form a single audio track ? That is, no additional processing is required, except for copying channels buffers from several AVFrames of different audio tracks to new positions of one AVFrame according to the new layout and aligning the timestamps of different audio tracks, since different audio tracks can have audio frames of different sizes with different timestamps.

  


  For example, 1 audio track with 2 channels and 2 audio tracks with 6 channels will be merged into 16 channels with silence in the "missing" channels. Or 4 audio tracks with 2 channels merged into 8 channels. Etc...

  


  Is there a way to use a avresampler for this ? Or a avfilter ? Or something else ?

  


  Any source code or any reading source that can help me is welcome.

  


• How to detect a common scene in a set of videos with ffmpeg

  6 août 2019, par Hans J

  I have a set of videos that are assumed to contain a common (or very similar) scene. I want to be able to detect (with FFmpeg) what that common scene is, how long the scene is, and where the scene is in each individual video.

  The scene would be assumed to be longer than 10 seconds (This is an arbitrary choice, it can be changed).

  The final output of the command would include the various time-codes of the instance of the scene in each video. Assuming a timebase 1/1, with a common scene that is 60 seconds long, an output would along the lines of :

  Video1.mp4 0 60
  
  Video2.mp4 120 180
  
  Video3.mp4 50 110
  
  Video4.mp4 null

  where video4 does not contain any common scene.

  For example, I could have three episodes of a TV show. They all contain the same commercial. Without knowing what that commercial is, I want to be able to find where that commercial shows up in each of the episodes.

  Note : For the purpose of a good solution, the common scenes do not have to exactly match. Because there could be artifacts or embedded subtitles in one episode and not the other.

• How do I preserve side data when concatenating files in ffmpeg ?

  28 mai 2020, par Mark Kahn

  I have multiple 360 videos that I'm trying to concatenate in ffmpeg. The command it self is pretty straightforward :

  



  ffmpeg -f concat -i 0036_concat.txt -c copy -strict unofficial 36.mp4


  



  where 0036_concat.txt is just a list of the individual files. The issue I'm having is that I can't get ffmpeg to preserve side data. Very simply put, ffprobe on any of the source files includes this :

  



  Side data:
  spherical: equirectangular (0.000000/0.000000/0.000000)


  



  And I can't, for the life of me, get that to propagate to the output file.

  



  this question has a solution that works for single files, but it doesn't work when concatenating multiple files.

  



  I'd be perfectly fine injecting that entire string if anyone knows how.