title: ffmpeg output Filename from multiple source
body: <p>I want to have the output file to have same name from source ( for eg first filename from <code>list.txt</code>), how can I do it?</p>
  
  <p>This is the code I have which converts the all the .avi in folder to a single files and renames it to <code>output.avi</code>.</p>
  
  <p>Instead of <code>output.avi</code> I want the filename to be same as first filename from source folder or first filename from <code>list.txt</code>.</p>
  
  <pre><code>for %%f in (*.avi) do (
      echo file %%f &gt;&gt; list.txt
  )
  ffmpeg -f concat -safe 0 -i list.txt -c copy output.avi
  del list.txt
  </code></pre>
  
  <p>One more thing I want to know, is it possible to flip video horizontal or mirror it without re-encoding?</p>