Missing required codecs is a big culprit to MP4 no sound error when playing MP4 files with Windows Media Player, QuickTime, VLC media player, or other players.
Install Required Audio Codecs for MP4 Playing If you are using earphones, you should make sure that they are properly plugged in and working. Also, check the audio settings on your computer to ensure that the volume is turned up and not muted. You have to ensure that the audio is not muted or turned off in the media player you are using, like Windows Media Player, QuickTime, VLC, etc. Check the Audio Settings to Fix MP4 No Sound Error