ffmpeg

concatenate videos

$ cat mylist.txt
file '/path/to/file1'
file '/path/to/file2'
file '/path/to/file3'

$ ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.mp4

convert video

ffmpeg -i LostInTranslation.mkv -codec copy LostInTranslation.mp4

ffmpeg -i "input.mkv" -vn -c:a libmp3lame -q:a 2 "output.mp3"

reduce image size

ffmpeg -i input.jpg -q:v 10 output.jpg