[FFmpeg-user] Possible to speed up/down video while keeping audio pitch?

[Laine Lee]

> On Mar 24, 2024, at 5:31 PM, Bo Berglund <bo.berglund at gmail.com> wrote:
> 
> I know how to use ffmpeg to adjust the video/audio sync and that is a real
> simple command not requiring any remuxing or such. This is what I use in my
> audiosync script and it runs very fast:
> 
> ffmpeg -i $SOURCEFILE -itsoffset $DELAY -i $SOURCEFILE -map 1:v -map 0:a -c copy
> $TARGETFILE
> 
> 
> But is it possible also to modify an mp4 video file to *play* faster/slower than
> original while keeping the accompanying audio pitch the same?
> 
> It *can* be done for instance in the VLC video player on playback, but can one
> also modify the video file itself using ffmpeg so it will play at the new speed
> while keeping audio recognizable (not Donald Duckie)?
> 
> If so how is it done?
> 
> 
> --

Sounds to me as though you want to change tempo of the audio stream. I believe there’s a pipe from ffmpeg to Sox to handle it, but for that you will extract audio, apply the tempo change, then remux. Changing tempo by a factor greater than one reduces duration, and by a factor less than one increases duration.

L. Lee