[FFmpeg-user] How to slow down a video

[Michael Koch]

Am 04.05.2020 um 11:00 schrieb 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.

try  -af aresample=48000

Michael