[FFmpeg-user] How to slow down a video

[Edward Park]

Hi,

> But I'm lost how use it correctly. I want to slow down the video by 1.4 and then increase the audio frequency (pitch) by 1.25.


So if you slow the video down by 1.4, You are also slowing down the audio by the same amount right? I think 1/1.4, and to add to the pitch to 1.25 ratio you'd have to multiply by 1.75, using filters to change frequency/pitch, librubberband has a simple pitch ratio factor you can multiply to whole spectrum. Or you could resample to your output format rate * 0.8 (1/1.25) then asetrate to the output sample rate after strectching/shrinking the audio to be 1.25 times the video length I think it will have a similar effect.

For example, slowing the video down could be -vf setpts=1.4*PTS, and for audio -af atempo=1/1.25/1.4,aresample=36000,asetrate=48000

Regards,
Ted Park