If you want to use ffmpeg to crop a video into multiple parts and then merge all the crops into one video,
Then you can execute:
ffmpeg -i input -filter_complex "[0:v:0]select='between(t,10.5,12.0)+between(t,12.5,15.0)+between(t,17.5,20.5)',setpts=N/FRAME_RATE/TB[outv]; [0:a:0]aselect='between(t,10.5,12.0)+between(t,12.5,15.0)+between(t,17.5,20.5)',asetpts=N/SR/TB[outa]" -map "[outv]" -map "[outa]" output.mp4
or execute:
ffmpeg -i input -filter_complex "[0:v:0]select='between(t,10.5,12.0)+between(t,12.5,15.0)+between(t,17.5,20.5)',setpts=N/FRAME_RATE/TB;[0:a:0]aselect='between(t,10.5,12.0)+between(t,12.5,15.0)+between(t,17.5,20.5)',asetpts=N/SR/TB" output.mp4
This instruction means to crop the three time periods of the video from 10.5s to 12 seconds, from 12.5s to 15s, and from 17.5s to 20.5s, and then merge these three time periods into one output.mp4 file.
Note: input is the path where the video needs to be cropped