If you can't hear the video, check the volume on the video player, your device, and on your earphones.
Also, check your network to see if you are having any other problems connecting to the Internet.
If you can't hear only certain videos, there may be a problem with the uploaded video. Please contact the holder (video sharer).
Note
If you can't hear the audio after trying all the above steps, close beSTREAM, remove the browser cache, and then try opening beSTREAM again.