Weak voice while recording on camera.

Hello everyone. Please help me with this issue on my iphone 6s plus. Why is my voice weak when im recording in the camera application of my iphone but when i used the camera on a third party app like on instagram, facebook, messenger, or snapchat, my voice is loud. Is this a software problem? Should I reset my phone? Or is this a hardware issue that I should fix by going to some technician? Thanks in advance for the answers. ❤️