title: How do I resolve ffmpeg concat command error "unknown keyword..."?
body: <p>I am trying to concatenate two video files using ffmpeg, and I am receiving an error.</p>
  <p>To eliminate compatibility issues between the two videos, I have been concatenating the same video with itself, and the same error persists.</p>
  <pre><code>ffmpeg \
    -f concat \
    -safe 0 \
    -i intro_prepped.avi intro_prepped.avi \
    -c copy \
    concat.avi  
  </code></pre>
  <p>And the error output I receive is....</p>
  <blockquote>
  <p>[concat @ 0x220d420] Line 1: unknown keyword 'RIFFf�?'
  intro_prepped.avi: Invalid data found when processing input</p>
  </blockquote>
  <p>I have tried various combinations of concat flags and have not been able to get it to work. Has anyone seen this error before?</p>