My Iphone 5 Playsback video with no sound?

Recently when I recorded some videos, I play them back but no SOUND but hissing noises. Its really frustrating cause I do alot of recordings… Tried resetting to factory 3times and did everything possible…

Seems like there's a problem with either the microphone which records the sound with the video or the speaker.
Better get it checked and fixed.
And try restoring it through iTunes which will reinstall the ios and it may fix the error.
If it still persists, get it checked and fixed.