Why my phone audio reducing to minimum often?

[AC Question]

When I am trying to play movie, music or any videos with full volume. It is playing with full volume for few seconds later it is reducing to minimum volume. It works well with headphone, but not in speaker. Please provide a solution, I have spent more money on this phone but facing many problems.

 

[B. Diddy]

Welcome to Android Central! Which phone? Does the problem persist in Safe Mode?