title: ffmpeg: concatenate videos of different frame rates?
body: <p>I store some N number of videos in a text file <code>list.txt</code> like so:</p>
  
  <pre><code>file /tmp/eef3e563eb32.mp4
  file /tmp/video_152.mp4
  file /tmp/video_153.mp4
  file /tmp/video_154.mp4
  file /tmp/video_155.mp4
  </code></pre>
  
  <p>The <code>video_</code> files are 30fps, the others are 60fps. When I try to concatenate them doing:</p>
  
  <pre><code>/usr/local/bin/ffmpeg \
      -loglevel panic \
      -y \
      -f concat \
      -safe 0 \
      -an \
      -i /tmp/list.txt \
      "out.mp4"
  </code></pre>
  
  <p>The <code>out.mp4</code> plays the 60ps one (first) fine, then the 30fps ones are all 2x speed.</p>
  
  <p>How can I resolve this? Can I add options in <code>list.txt</code> or do I need a more complex solution with <code>ffmpeg</code>?</p>