[FFmpeg-user] How to slow down a video

[Ulf Zibis]

Am 27.03.20 um 04:06 schrieb Ted Park:
> Hi,
>
>> for video: -vf setpts=0.5*PTS
>> for audio: -af atempo=2
>
> Actually, he wanted to slow down the video so you probably meant the reciprocal of this, 2*PTS and atempo 1/2

Thanks alot, this works fine.

Now I want to tweak a little bit more. I want to slow down the video by 1.4 and then increase the audio frequency by 1.25. So I did:
ffmpeg -i in.mp4 -vf setpts=PTS*1.4 -af asetrate=48000*1.25,atempo=1/1.25/1.4 out.mp4

This resulted in really bad audio quality. The reason is maybe, that the sampling rate of the output was transformed to 64.000, but I want 48.000. I guess there is a possibility to get a better result by using -af aresample, but I have problems to understand it's syntax.

Can one please give me a hint for my purpose?

-Ulf