My videos on my iPhone 4S has no sound?

Okay YouTube videos sounds ringtones and message sounds works except my videos I can her the backing sounds but not my voice how can I fix it. It's really annoying

You should turn off/on your phone and see if its fixed. If there's something wrong with your phone, you should get it to a phone fixer guy (sry i don't know what its called) and get it checked up.

That happened to my friends iPhone4 and she had to send it away to be fixed.