title: merge multiple videos and audios with ffmpeg
body: <p>I have used the program <strong>youtube-dl</strong> to download a Youtube playlist, i have chosen to download videos and audios separately, i have now a folder full of videos with their corresponding audios that i wish to merge together with ffmpeg.</p>
  
  <p>I need to do this using a batch script but the problem is that youtube-dl added aleatory letters after the original file's title so the videos doesn't have the same name as their corresponding audio, file names looks like this:</p>
  
  <pre><code>First title in the playlist 5J34JG.mp4
  First title in the playlist H3826D.webm
  Second title in the playlist 3748JD.mp4
  Second title in the playlist 6SHJFZ.webm
  </code></pre>
  
  <p>How to merge these multiple video/audio files using windows batch script and ffmpeg ?</p>
  
  <p>Edit: I forgot to mention that the .webm files are the audio files and that i have multiple files i can't rename them one by one.</p>