title: how to fix error Requested output format 'concat' is not a suitable output format
body: <p>This is my command</p>
  
  <pre><code>ffmpeg -f concat safe 0 -i C:\_source\mergethis.txt -c copy C:\_combined\combined.mp4
  </code></pre>
  
  <p>I get this error</p>
  
  <pre><code>[NULL @ 00000000022a5060] Requested output format 'concat' is not a suitable output format
  safe: Invalid argument
  </code></pre>
  
  <p>mergethis.txt contains this</p>
  
  <pre><code>file C:\\_source\\01.mp4
  file C:\\_source\\02.mp4
  file C:\\_source\\03.mp4
  file C:\\_source\\04.mp4
  file C:\\_source\\05.mp4
  file C:\\_source\\06.mp4
  </code></pre>