90.5 Video Cut and Slice
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To cut a segment of video to a file, starting at the 30 seconds mark and going until 40 seconds:
ffmpeg -i orig.mp4 -ss 00:00:30 -to 00:00:40 -c copy output.mp4We can illustrate the more complex task of cutting out sections of a video and splicing them together. As a use case we want to illustrate the effect of a 8dB boost to the audio track of the video and to do this for a 10s segment of the original and boosted video.
We can first boost the audio by 8dB and save the result to a new file.
ffmpeg -i orig.mp4 -vcodec copy -af "volume=8dB" plus8db.mp4We now have two videos and we want to cut 10 seconds of video from 30 seconds into the video, for both videos and to then splice them together. As a bonus we will add an overlay of text to be able to identify each section.
ffmpeg -i orig.mp4 -i plus8db.mp4 -filter_complex "[0:v]trim=start=30:end=40,setpts=PTS-STARTPTS[v0];[1:v]trim=start=30:end=40,setpts=PTS-STARTPTS[v1];[0:a]atrim=start=30:end=40,asetpts=PTS-STARTPTS[a0];[1:a]atrim=start=30:end=40,asetpts=PTS-STARTPTS[a1];[v0]drawtext=text='ORIGINAL':fontsize=24:fontcolor=black:x=(w-text_w)/2:y=h-th-20[with_text_0];[v1]drawtext=text='INCREASED':fontsize=24:fontcolor=black:x=(w-text_w)/2:y=h-th-20[with_text_1];[with_text_0][a0][with_text_1][a1]concat=n=2:v=1:a=1[outv][outa]" -map "[outv]" -map "[outa]" output.mp4The work is done by the complex filter.
[0:v]trim=start=30:end=40,setpts=PTS-STARTPTS[v0]; This trims the
video stream from the first input file [0:v] to the 10 seconds from
30 seconds in to 40 seconds in and resets the presentation timestamps.
[1:v]trim=start=30:end=40,setpts=PTS-STARTPTS[v1]; Similarly for the
second video [1:v].
[0:a]atrim=start=30:end=40,asetpts=PTS-STARTPTS[a0]; Similarly for
the audio from the first video [0:a].
[1:a]atrim=start=30:end=40,asetpts=PTS-STARTPTS[a1]; Similarly for
the audio from the second video [1:a]
[v0]drawtext=text='ORIGINAL':fontsize=24:fontcolor=black:x=(w-text_w)/2:y=h-th-20[with_text_0];
For the first video segment [v0] we add the text ORIGINAL with font
size 24 and colour black. The x location is determined so as to centre
the text and the y location will place the text 20 pixels above the
bottom of the frame.
[v1]drawtext=text='INCREASED':fontsize=24:fontcolor=black:x=(w-text_w)/2:y=h-th-20[with_text_1];
Similarly for the second video segment [v1].
[with_text_0][a0][with_text_1][a1]concat=n=2:v=1:a=1[outv][outa]
Here we splice then together.
The -map "[outv]" and similarly for the audio maps the output video
and audio streams to be included in the final output.
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