Find duration only with ffprobe in Windows
First, if you just want information about a file, you should probably use &quot;ffprobe&quot;, not &quot;ffmpeg&quot;. Otherwise you'll get an answer, but you'll also have an error return status.
As to your real question: By convention, ffmpeg reserves STDOUT for binary video and audio data only. Everything else, including all the possible kinds of informative text, is sent to STDERR.
So, try changing your code to:
ffprobe FILENAME.EXT 2| find &quot;Duration:&quot;  (for a *nix shell)
or
ffprobe.exe FILENAME.EXT 2&gt;&amp;1 | findstr Duration (for a Windows shell)