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I'm trying to use slow motion effect on my videos. Let's say I have a 2 minutes long video and I want to use this effect between 20 and 30 seconds.

I found this command from a blog: 

ffmpeg -i input.mp4 -vf "setpts=(<speed>/1)*PTS" output.mp4

But i don't know how to implement duration in it.

nixda
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iwocan
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1 Answers1

11

The setpts filter does not have timeline editing functionality like some of the other filters (refer to ffmpeg -filters to see which do).

This means you will have to make a slow video and concatenate it into your normal speed videos or perform some fancy filtering.

Example: video only

Using the trim, setpts, and concat filters:

The input in this example has a duration of 60 seconds. 0-10 will be normal speed, 10-30 will be 50% slower, and 30-end will be normal speed resulting in an output with a duration of ~80 seconds:

ffmpeg -i input.mkv -filter_complex \
"[0:v]trim=0:10,setpts=PTS-STARTPTS[v1]; \
 [0:v]trim=10:30,setpts=PTS-STARTPTS[v2]; \
 [0:v]trim=start=30,setpts=PTS-STARTPTS[v3]; \
 [v2]setpts=PTS/0.5[slowv]; \
 [v1][slowv][v3]concat=n=3:v=1:a=0[out]" \
-map "[out]" output.mp4

Example: with audio

ffmpeg -i input.mkv -filter_complex \
"[0:v]trim=0:10,setpts=PTS-STARTPTS[v1]; \
 [0:v]trim=10:30,setpts=PTS-STARTPTS[v2]; \
 [0:v]trim=start=30,setpts=PTS-STARTPTS[v3]; \
 [0:a]atrim=0:10,asetpts=PTS-STARTPTS[a1]; \
 [0:a]atrim=10:30,asetpts=PTS-STARTPTS[a2]; \
 [0:a]atrim=start=30,asetpts=PTS-STARTPTS[a3]; \
 [v2]setpts=PTS/0.5[slowv]; \
 [a2]atempo=0.5[slowa]; \
 [v1][a1][slowv][slowa][v3][a3]concat=n=3:v=1:a=1[v][a]" \
-map "[v]" -map "[a]" output.mp4

slowmoVideo

Alternatively you could try slowmoVideo which will probably result in a better looking slowdown effect compared to ffmpeg alone (slowmoVideo uses ffmpeg). It also allows you to use Bézier curves to plot the effect so you can smoothly initiate the effect, and it can include motion blur.

llogan
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