ffmpeg -i LostInTranslation.mkv -vcodec copy -acodec copy LostInTranslation.mp4

The same in a loop:

for i in *mkv; do ffmpeg -i $i -vcodec copy -acodec copy $i.mp4; done

sudo apt install youtube-dl

Download vidéo:

Download mp3 only:

youtube-dl –ignore-config -o '~/Music/%(uploader)s - %(title)s.%(ext)s' –extract-audio –audio-format mp3 –audio-quality 5 <youtube code or URL>

for f in *.flac; do flac -cd “$f” | lame -b 128 - “${f%.*}”.mp3; done