can't record videos from front camera iphone 6 plus

Hi,
right now i am using iphone 6 plus ios version 8.3. I have been using this phone since 3 months and haven't had no problem but now i am having an issue regarding a video recording. I came to know about this issue from a software called viber. I called my mum from viber everything was fine but as soon as i made loud speaker my mum can't hear my voice so i thought it might be the viber problem so i wished to check my microphone and checked the video recording from rear camera and in voice memo. Everything worked like a charm but today morning i tried to record video from my front camera and played the video but there was no sound it just sounds like hisssss. I thought it would be a software problem so i updated the software to 8.2 but still the same issue. Anybody knows about this problem or can fix it?? I don't want to ruin my phone its just 3 month old. Please....