I have iphone 7 i which recorded video's sound becomes very low sometimes and then become normal. This is below audible in sometimes. Please help

Hi there, kamalfromtanakpur!
Thanks for reaching out to the Apple Support Communities! It sounds like you are having an issue with videos recorded and the sound not working properly and I am happy to help out! Take a look at this article with the best steps to follow to Get help with the microphones on your iPhone, iPad, and iPod touch. This article will give you steps you can try to troubleshoot your issue along with the nest steps to take if the issues continue.
Cheers!