[FFmpeg-devel] Atempo limits

[Pavel Koshevoy]

On 06/04/2018 12:09 PM, Ronak wrote:
> Hello,
>
> How are you all?
>
> We are looking to use the atempo filter for our audio files. However, the limit between 0.5 - 2x is too restrictive for us. We would like to expand the limit to 0.5x - 3x.
>
> I tried changing the range in atempo.c and the rest of the tempo filter just worked.
>

Going below 0.5 is likely not going to sound good. Going above 2.0 should be 
fine.  The reason for current [0.5, 2.0] range is mostly for symmetry. 
atempo=0.5 followed by atempo=2.0 should sound like original audio.  This should 
also point you to an alternative solution -- put 2 atempo filters one after 
another to achieve tempo greater than 2  (atempo=2.0,atempo=1.5), or like this:

ffmpeg -i /scratch/Music/02\ Feeling\ Good.mp3 -af 
'atempo=sqrt(3.0),atempo=sqrt(3.0)' -y /tmp/tempo-3x.wav

   Pavel.