[FFmpeg-devel] Exposing preroll and remainder info for aac and mp3.

Nicolas George nicolas.george at normalesup.org
Wed Jul 4 16:05:17 CEST 2012

Le septidi 17 messidor, an CCXX, Michael Niedermayer a écrit :
> are there some reference files (mp3/aac + wav refernce of what should
> be the delay free output ?)
> These would be very usefull to implement this as well as for
> regression tests so it doesnt break in the future once it works.

Is it really necessary? We can see for ourselves with any audio file that
does not have too much silence on the beginning. For example:

ffmpeg -f lavfi -i aevalsrc='abs(sin(2*PI*t))*sin(2*PI*440*t)::d=10' \
  test.mp3 test.wav
ffmpeg -i test.wav -i test.mp3 -filter_complex '
  [0:0] showwaves=n=15:s=1470x64, pad=iw:ih*2 [a] ;
  [1:0] showwaves=n=15:s=1470x64 [b] ;
  [a] [b] overlay=0:64' -vframes 1 test.png

The output.png shows clearly a 74 pixels delay for the MP3 file, which makes
about 1110 samples.

I believe our purpose should be that a round trip encode+decode gives a file
that is in sync with the original. lame + lame --decode does that, for


  Nicolas George
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