user30421: I want to find video file duration only with ffprobe but
ffprobe FILENAME.EXT 2| find "Duration:" 

does not filter output to show just the line with "Duration:"  Instead, I got:

Argument '2' provided as input filename, but 'FILENAME.MP4' was
already specified.

How do I see just the duration of a file from the Windows command prompt?

user30649: First, if you just want information about a file, you should probably use "ffprobe", not "ffmpeg". 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 "Duration:"  (for a *nix shell)
or
ffprobe.exe FILENAME.EXT 2>&1 | findstr Duration (for a Windows shell)

30421: <p>I want to find video file duration only with <a href="https://ffmpeg.org/ffprobe.html" rel="nofollow noreferrer">ffprobe</a> but</p>
<pre><code>ffprobe FILENAME.EXT 2| find &quot;Duration:&quot; 
</code></pre>
<p>does not filter output to show just the line with <strong>&quot;Duration:&quot;</strong>  Instead, I got:</p>
<blockquote>
<p>Argument '2' provided as input filename, but 'FILENAME.MP4' was
already specified.</p>
</blockquote>
<p>How do I see just the duration of a file from the Windows command prompt?</p>
 30649: <p>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.</p>
<p>As to your real question: By convention, ffmpeg reserves STDOUT for binary video and audio data <em>only</em>. Everything else, including all the possible kinds of informative text, is sent to STDERR.</p>
<p>So, try changing your code to:</p>
<p><code>ffprobe FILENAME.EXT 2| find &quot;Duration:&quot;</code>  (for a *nix shell)</p>
<p>or</p>
<p><code>ffprobe.exe FILENAME.EXT 2&gt;&amp;1 | findstr Duration</code> (for a Windows shell)</p>
