n=25; ffmpeg -i ical$n.mp4 ical$n'!'.mp4 && mv  ical$n'!'.mp4 ical$n.mp4; ffmpeg -safe 0 -thread_queue_size 4096  -f concat -i <(printf "file '%s'\n" $PWD/slate.mp4; printf "file '%s'\n" $PWD/ical*4 | grep -ve 5zc -e 17aP -e 17aCc | sort -V) -c copy iall.mp4