While playing back videos or if i am using the phone, the sound either automatically reduces in volume to about 1/2 or cuts out completely.  If I do nothing, after a few minutes, the sound returns to normal but then goes back down.  I have to stop and restart the video a couple of times to get the sound back (when it cuts out completely) however the problem still exists.  Also, I notice that when I disable the WiFi, I can not re-enable it without rebooting the phone.

Hi.
Go to the dial interface and dial "*#87#" and it can to calibrate the sound.
More phone issues, you can contact our professional after-sales directly. 
After-sales email: support02@blackview.hk
Have a nice day!

This is not calibration and it doesn't work. This is software problem and you need to fix it. Also is there second speaker? Because only one gives sound