I have an example

ffmpeg -i zs_712922_CT.mp4 -itsoffset 10 -i ct.m4a -map 0:0 -map 1:0 -c:v copy -preset ultrafast -y out1.mp4 (I don't know why this dropped the video, leaving only the audio.)


ffmpeg -i input.mp4 -itsoffset 10 -i ct.m4a -map 0:0 -map 1:0 -itsoffset 50 -i ct.m4a -map 0:0 -map 1:0 -c:v copy -shortest -y out.mp4


ffmpeg -i zs_712922_CT.mp4 -itsoffset 10.555 -i ct.m4a -itsoffset 20.999 -i ct.m4a -itsoffset 70 -i ct.m4a -map 0:1 -map 1:0 -map 2:0 -map 3:0 -c:v copy -preset ultrafast -f mp4 -y out1.mp4

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  • You can copy the audio. And this method relies on edit lists in the MP4, which some players, like WMP, don't support. – Gyan Jul 16 '18 at 6:07

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