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• Determine which decoders/demuxers/parsers ffmpeg needs to successfully consume file

  10 octobre 2024, par rschristian

  I'm trying to custom compile a build of ffmpeg.wasm as the prebuilt, "support everything" is a tad hefty at 35mb. This base build (as well as standard ffmpeg, running on my desktop) works perfectly fine for the provided file, however, so I do have something I can work against.

  


  My issue is that I'm a bit stuck on figuring out what precisely I need to support the provided file, the correct combination of decoders, demuxers, parsers, etc., and the encoders, muxers I'll need to use to convert it to my desired output.

  


  I'm sure I can brute force this with time, but is there a way of having ffmpeg report precisely which combination it's using when running against a file ? I've tried -report but it doesn't seem to contain this information, really it contains no more useful codex information than the standard output log as far as I can tell.

  


  For example, I can see the current file I'm testing with (foo.m4s) is h264 video and aac audio, so I tried the following flags based on what I've been able to find online and by looking through the list of muxers :

  


  --enable-decoder=aac,h264
--enable-demuxer=aac,h264
--enable-parser=aac,h264


  


  However, this results in the following error :

  


  foo.m4s: Invalid data found when processing input


  


  So it seems like it's not quite the correct list.

  


  Is there any good way to debug this ? Some way of having ffmpeg itself report exactly what I'll need set to handle this conversion using my own compilation ? As the goal is a minimum build, adding the kitchen sink and slowly reducing over time will obviously be super time consuming, so I'd like to avoid it if at all possible.

  


  ---

  


  Edit : Trial and error got me down to this, though I don't quite understand it (and the question still stands as I could reasonably need to handle other files in the future) :

  


  --enable-demuxer=aac,mov
--enable-parser=aac


  


  mov for some reason ended up being the fix ? The first line of ffmpeg's output was Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'foo.m4s', and so I simply grabbed those one-by-one and sure enough mov worked, despite the video having h264. Would love if someone could explain this too.

  


• What can be the substitute for SDL to direct ffmpeg decoded videos to screen in IOS ?

  18 octobre 2012, par jAckOdE

  I making a iOS video player using ffmpeg, the flow likes this :

  Video File---> [FFMPEG Decoder] —> decoded frames —> [a media director] —> /iphone screen (full and partial)/

  A media director will handle the tasks of rendering decoded video frames to iOS ui (UIView, UIWindow etc), outputting audio samples to iOS speaker, and threads management.

  SDL is one of those libs, but SDL is mainly made for game making purpose and seem to be not really mature for iOS.

  What can be the substitute for SDL ?

• Warp video and audio non-linearly with ffmpeg

  25 novembre 2016, par Simon Streicher

  I have a non-linear mapping of the time-locations of an input video to be warped to the time-locations of an output video. Here is an example :

  

  I therefore want to take the input video and this mapping and accelerate-and-decelerate appropriately to produce the output video (audio included). Is there any functionality in ffmpeg to accomplish this ? Any frame interpolation may be nearest neighbour or something silly (it doesn’t need to look good), but I would prefer something sophisticated for the audio.

  I have Python along with the whole numpy-scipy stack to my disposal to convert this mapping to something more parseable by ffmpeg.