I recently wanted to trim and fade out an MP4 file. I wasn’t inclined at the effort of putting it in a non-linear editor and was looking for a quick way to achieve this.
I found that ffmpeg had the necessary functionality to do this. The command I used in the end was:
ffmpeg -i in.mp4 -ss 00:00:00 -t 00:05:00 -vf "fade=t=out:st=297:d=3" -af "afade=t=out:st=297:d=3" out.mp4
The commands are:
-i in.mp4is the input file
-ss 00:00:00is where the video should start from (set this to other than zero to trim the start)
-t 00:05:00is the duration of the video, trimming any video after that
-vf "fade=t=out:st=297:d=3"is a video filter which fades out at 297 seconds (4:57) over a 3 second duration
-af "afade=t=out:st=297:d=3"is the corresponding audio filter which fades out at 297 seconds (4:57) over a 3 second duration
out.mp4is the output file
The video and audio filters have several more properties you can play with, such as if you want to fade to white using a log curve for the audio fade.
You can also combine filter commands by separating them with a comma, if you want both a fade in and fade out, for example:
-vf "fade=t=in:st=0:d=3,fade=t=out:st=297:d=3" -af "afade=t=out:st=0:d=3,afade=t=out:st=297:d=3"
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