Screen recording video has no sound when exported

In regards to this question "My screen recording videos will play the microphone audio (i.e. talking/ambient sound) along with app audio (in-game sounds) when played in the Photos app or when sent via iMessage.

However, when exported to any other app -- Instagram, Twitter, Youtube, Tumblr, even iMovie -- the videos only have the app audio and no external sound".

A SOLUTION that worked for me was disabling silent mode on the iPhone device and voila the sound works when uploading video to Social sites