Invoking ffmpeg iteratively

Question

I call ffmpeg like this from Mac's terminal:

$ find . -type f -name *.webm | while IFS= read -r f; do echo "$f"; ffmpeg -i "$f" "${f%.webm}".mp4 2> ~/Desktop/err; done

Only the first file returned by find gets processed:

./artist/Moody Blues/_vid/Nights in white satin_lyrics.webm

Excerpt from err:

Enter command: |all |-1 [ ]

Parse error, at least 3 arguments were expected, only 1 given in string 's [360p].webm'

Enter command: |all |-1 [ ] Parse error, at least 3 arguments were expected, only 1 given in string 'hannel/Ash Wainman/_Inbox/BOHEMIAN RHAPSODY - ASH WAINMAN[HD,1280x720].webm'

We should have 'channel' rather than 'hannel'.

Answer 1

As LordNeckBeard suggests, adding -nostdin stops ffmpeg from attempting interaction (or, apparently, reading its inherited stdin.)

This is touched on in the man page:

-stdin
       Enable interaction on standard input. On by default unless standard input is used as an input. To explicitly disable interaction you need to specify "-nostdin".

       Disabling interaction on standard input is useful, for example, if ffmpeg is in the background process group. Roughly the same result can be achieved with "ffmpeg ... <
       /dev/null" but it requires a shell.

Answer 2

You're improperly using find and needlessly creating a shell loop (it hurts to read!), because you can (should) run ffmpeg directly from inside find:

find . -type f -name *.webm \
-exec sh -c 'echo "$1"; ffmpeg -nostdin -i "$1" "${1%.webm}".mp4 2>> ~/Desktop/err' sh {} ';'

With deference to LordNeckBeard (though mine is assuredly hairier).