title: Bash - control external command's output
body: <p>I'm writing a bash script to make DVD authoring more automated (but, mainly, so that I can learn some more bash scripting) and I'm trying to find out if it's possible to control how an exterrnal command presents its output.</p>
  
  <p>For instance, the output from ffmpeg is a load of (to me) irrelevant cruft about options, libraries, streams, progress and so on.</p>
  
  <p>What I really want is to be able to select for display only the lines with the input and output filenames and then to display the progress on the same line each time.  Similarly for mkisofs and wodim.</p>
  
  <p>I've tried Googling for this and am beginning to suspect that either it's not possible or nobody's thought of it before (or, possibly, that it's so obvious that nobody thinks it necessary to say how  :-) ).</p>
  
  <p>Many thanks, in advance,</p>
  
  <p>David Shaw</p>