Why my samsung tv sometimes do not play audio while a video is running


Hi, it is a weird problem that i face. I download some mp4 file and then play it using the usb slots avaiable in my samsung tv. The video is playing with audio, but randomly the sound gets muted and video only plays. The format is mp4. The problem is resolved , when i revert to
av mode or cable mode to view the tv channel and then again go to the media mode.
Why it is happening at some times causing break in continuous viewing of video with sound.
i tried to convert them to avi format, old video format and still the problem persists.
There are only limited menus that could be adjusted using the tools in the internal mode like sound and picture size etc.
The tv channels thro cable or av mode is working perfectly.
When viewing in pc, there is no sound problem. please.
Of late, i found that my query does not get any reply from experts