Automating file conversions with ffmpeg

Question

I'm looking for a way to automate file conversions. I'm using an Ubuntu virtual machine through which I'm accessing a Windows installation. The normal syntax should be:

ffmpeg -i file.mp4 file.mp3

So this is what I'm trying to do:

ls | while read i; do echo ffmpeg -i \"$i\" \"${i/mp4/mp3}\"; done

As you can see I added "echo" to see the generated command first and this is what I get:

ffmpeg -i "Accepting Amendments.mp4" "Accepting Amendments.mp3"

As you can see, the file names may have spaces, so I'm trying to escape them. However this command doesn't work when I remove the "echo". What happens is only some conversions are made and I'm getting error messages with split file names such as "ccepting Amendments.mp4" for instance. So basically the first ffmpeg command runs fine, then the second one fails, and so on.

I've noticed that when I run an ls command, I'm getting filenames with single quotes, but when I create a file myself, there are no quotes.

$ls
'Accepting Amendments.mp4'
$touch test
$ls
'Accepting Amendments.mp4'
test

Could that be the issue?

Answer 1

No, the problem is that (by using \") you're telling ffmpeg to transform a file "Accepting Amendments.mp4", with quotation marks contained in the name. That file doesn't exist, so ffmpeg fails. What you really want to do is use unescaped quotation marks that the shell interprets as "don't split the contained value": ffmpeg -i "$i" "${i/mp4/mp3}"

Besides, instead of piping ls's output you can/should have the shell loop on its own:

for i in *.mp4; do ffmpeg -i "$i" "${i/mp4/mp3}"; done

With ffmpeg this still doesn't work properly, though, because it reads from stdin for some reason and seems to swallow some characters in the file names that way. The -nostdin flag helps:

for i in *.mp4; do ffmpeg -nostdin -i "$i" "${i/mp4/mp3}"; done

(The single quote you see in your ls output is added by your version of ls for file names that contain e.g. spaces, so that you can simply take that output on the command line as the argument for another program. That has nothing to do with who created the file, you just didn't trigger the behavior with your file named test.)