ffmpeg

Generate a clip

ffmpeg -y --ss start_time -to end_time -i input_file output_file

start_time / end_time format: 0:01:12.123 (1min 12 seconds 123ms)

-y: skip confirmation, can override file.

Merge clips

ffmpeg -y -f concat -safe 0 -i files.txt -c copy output_file

# files.txt
file ./clip1.mp4
file ./clip2.mp4