[FFmpeg-user] How to slow down a video

[Ulf Zibis]

Am 05.05.20 um 15:07 schrieb 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

Swapping aresample with asetrate is an interesting aproach. It seems to have very little better quality.

Aside I have a question: Where can I find a list of properties, which can be used as parameter in commands. E.g. I can use "PTS" for current picture time stamp and "h" for the heigth. In my case interesting: What is the parameter for the audio rate to use with asetrate=RATE*1.25 ?

-Ulf