title: Python Youtube-dl convert to mp4
body: <p>(if it matters, I'm on windows)</p>
  <p>So I am trying to download a Youtube video in an Mp4 format (the program I am putting it into has limited compatibility) with audio but whatever I find online either doesn't work how people are saying it does (leading me to believe it is either outdated, missing context, or for a different OS) or is formatted in a way that doesn't make sense.</p>
  <p>My current code is :</p>
  <pre><code>if PreferredOutput == 1:
      with youtube_dl.YoutubeDL({'format' : 'bestvideo+bestaudio[ext=m4a]/bestvideo+bestaudio/best', 'merge-output-format' : 'mp4'}) as ydl:
          ydl.download([url])
  </code></pre>
  <p>but when I test it, it just seems to output the file as normal.(which I am guessing is the format the video file was uploaded to youtube as though I could be mistaken) What should I do/am I missing to make this only output (final) Mp4s? (after the fact ffmpeg conversion or something similar is fine for my purposes)</p>