title: Encode mp4 video with just audio
body: <p>I am working on a cordova app for iOS and Android and the app works on all devices I've tested except the OnePlus, where the audio does not work but the video does.  I've tried ogg and mp3 but to no avail.  However, mp4 videos play perfectly.</p>
  
  <p>As a hackish solution, I'd like to make all of my audio mp4 video that has no images and just audio.  Is this possible using ffmpeg or another too and will it play in the video tag?  If all else fails I can create a video with a single stock image, but I'm afraid that the result will be larger than what I'm looking for.</p>