[FFmpeg-user] Converting mkv to mp3 failures

[Hans Carlson]

On Fri, 14 Jul 2017, Moritz Barsnick wrote:

>> done < VIDEO_FILES  > FFMPEG_ERRORS 2>&1
>
> I don't know why, but I have seen it before, and the '< VIDEO_FILES' may 
> be flooding ffmpeg's stdin. Do try "-nostdin".

This is a common problem with bash/sh and "while" loops.  The while loop 
is reading from STDIN and any commands within the loop are reading from 
the SAME STDIN.  When you redirect STDIN to the while loop, you also 
redirect it to the commands within the loop.  In this case, that means 
both the while loop and ffmpeg are competing to read from "VIDEO_FILES".

As you suggest, -nostdin should fix this... it'd think anyway.  If not, it 
should work to redirect STDIN to the ffmpeg command, eg:

   while ...
     ffmpeg ... < /dev/null
   done < SOME_FILE

If you really need the command within the loop to read from STDIN, then 
you need to get trickier and start playing around with file descriptors. 
A better option is just to use perl or some other scripting language that 
handles this better.