title: Using FFMPEG concat to produce a short output video
body: <p>I need to concatenate 306 images using FFMPEG.
  so, I proceed with the following script shell :</p>
  
  <pre><code>touch input.txt
  
  for i in `seq 0 305`;
  do
    echo "file $i.png" &gt;&gt; input.txt
    echo "duration 1" &gt;&gt; input.txt
  done
  
  echo "file 305.png" &gt;&gt; input.txt
  
  ffmpeg -f concat -i input.txt -vf fps=10 -vsync vfr -pix_fmt yuv420p video.mp4
  </code></pre>
  
  <ol>
  <li>I can't find the right parameters for concat.</li>
  <li>I searching about duration, I can't find if it's possible to specify
  less than 1 second.</li>
  <li>Every time, I change fps, the duration of output video became so
  big; example: if fps = 10 , output video duration = 3060 seconds</li>
  </ol>
  
  <p>also, I tried :</p>
  
  <pre><code> 1. ffmpeg -f concat -i input.txt -vf fps=10 -vsync vfr -pix_fmt yuv420p
      video.mp4
   2. ffmpeg -f concat -i input.txt -y -vf fps=1 -crf 22 -threads 2
      -preset veryfast video.mp4
  </code></pre>
  
  <p>I tried also, with duration 1 for all images, the final video show only 1 image.</p>
  
  <p>I need to concat those images and produce a short output video. </p>
  
  <p>any idea </p>