Homepages Video Sound

Hello, i have this question:

I use a video which is throwed by visual composer,
unfortunately the video’s sound is only played some times. Can’t find when is this happening, i mean, sometimes i press F5 and there is it, so i scroll to see the video and it dissapears…. Mostly time i have no sound.

Any ideas about?

If helps its a video from YouTube, i’ve tested other videos without result.

WordPress version 4.7.3
PD: If you have no ideas about this, it would help if someone could tell me which file have to edit to use JavaScript to allow the sound in hard code.
Thx a lot
Regards