CODEWITHSUNDEEP
linuxvideoscriptingffmpegvideo-editing
Zach Bloomquist
Zach Bloomquist

Reputation: 5871

Combining videos with ffmpeg using crossfades and plain cuts

I am writing a script to combine/slice arbitrary video files from S3 into one output video. So far, I am doing this by first trimming the videos to their proper length using ffmpeg -i input-X.mp4 -ss start -t duration slice-X.mp4 and recombining the resultant slices with the ffmpeg concat filter.

I want to be able to crossfade and cut between videos. concat does not support transitions. What is the best way to combine videos with crossfades and cuts on the Linux command line? Is ffmpeg the best tool for the job?

My question is similar to "How do you create a crossfade transition between multiple videos in FFMPEG?" but I do not necessarily need to use ffmpeg. Also, I want to be able to fade in between some slices and cut between others.

Upvotes: 2

Views: 2564

Answers (2)

Gyan
Gyan

Reputation: 93028

Below is the single step command template, assuming five slices.

ffmpeg -i input.mp4 -i input.mp4 -i input.mp4 -i input.mp4 -i input.mp4 \
-filter_complex \
"[0:v]trim=0.5:4.5,setpts=PTS-STARTPTS[1]; \
 [1:v]trim=12:17,setpts=PTS-STARTPTS+(3/TB),format=yuva420p,fade=in:st=3:d=1:alpha=1[2]; \
 [2:v]trim=34.1:36,setpts=PTS-STARTPTS+(7/TB),format=yuva420p,fade=in:st=7:d=1:alpha=1[3]; \
 [3:v]trim=21:25,setpts=PTS-STARTPTS[4]; \
 [4:v]trim=27:31,setpts=PTS-STARTPTS+(3/TB),format=yuva420p,fade=in:st=0:d=1:alpha=1[5]; \
 [0:a]atrim=0.5:4.5,asetpts=PTS-STARTPTS[1a]; \
 [1:a]atrim=12:17,asetpts=PTS-STARTPTS[2a]; \
 [2:a]atrim=34.1:36,asetpts=PTS-STARTPTS[3a]; \
 [3:a]atrim=21:25,asetpts=PTS-STARTPTS[4a]; \
 [4:a]atrim=27:31,asetpts=PTS-STARTPTS[5a]; \
 [1][2]overlay,format=yuv420p[12]; \
 [12][3]overlay,format=yuv420p[123]; \
 [4][5]overlay,format=yuv420p[45]; \
 [1a][2a]acrossfade=d=1[12a]; \
 [12a][3a]acrossfade=d=1[123a]; \
 [4a][5a]acrossfade=d=1[45a]; \
 [123][123a][45][45a]concat=n=2:v=1:a=1[v][a]" \
-map [v] -map [a] SingleStepOutput.mp4

I have inputted the video multiple times, once for each slice, because using a single input pad (even with split/asplit) leads to buffer overflows.

The setpts/asetpts filters are used because trim/atrim carry over the original timestamps. The setpts filters are offset for the slices which have to fade in. The offset value is the preceding slide duration - crossfade duration. The yuva420p is needed to create an alpha channel whose value is actually modulated by the fade filter.

Upvotes: 4

Zach Bloomquist
Zach Bloomquist

Reputation: 5871

I ended up doing this by iterating on each slice and appending each to a temporary output file.

[output] <-- copy slice 1
[output] <-- cut slice 2 on to output
[output][slice 2] <-- fade slice 3 on to output
[output][slice 2][crossfade][slice 3] <-- fade slice 4 on to output, etc...

So it's n ffmpeg instructions to slice the input videos to the correct length, and then n-1 ffmpeg instructions to concatenate them all with appropriate transitions.

Upvotes: 0

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