Windows – How to use slow motion effect in a specific time interval with ffmpeg


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.

Best Answer

  • 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


    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 B├ęzier curves to plot the effect so you can smoothly initiate the effect, and it can include motion blur.

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