Iphone ios 7.1.2 after update two incident unable to control volume

Hi

Iphone 4 withafter updated to ios 7.1.2.

recently have two incident of volume control button unable to control the movie sound.

first incident happen off the phone for one day on back not sure how no problem in volume control.

this second incident recently happen on 2/5/2016, off the phone about two day, on back, fault still persist, reset all, fault still persist, hardware reset, fault still persist

but plug in headphone no issue to control the sound.

ringer no issue

bur all alert unable to hear any sound after select.

any can help to solve this?

Thanks