Q: HDMI no sound after an interval of time

Love my Macbook 12" as it replaces my desktop Mac Mini for everything.

Single connector USB-C to HDMI with sound output from a headphone jack routed to a amp from my BenQ XL2720Z Gaming monitor.

After boot up, sound seems normal from various activities like youtube, Facebook, some movie clips using mplayerx. However if I browse at long intervals without any sound output, I lose my sound. If I check my System Preferences/Sound, it is still showing that sound output is routed through my Displayport; nothing has changed. I tried plugging a headphone into the headphone jack to toggle the output but still no sound.

In order to reset this, in prior times turning the monitor off and on would work but no longer. Now I have to unplug the USB-C cable and replug it back it. You can hear the sound coming out of the internal speaker before routing back through the HDMi to my HDMI Headphone jack output.

Now I also use a program called InsomniaX to allow me to close my notebook.

The disappearance of sound after an interval of time happens with or without power. It could be a sound sleep problem of the Benq monitor in which if no sound output is detected it output through the headphone jack may automatically turn off (just guessing as there are no documented sound sleep output options). The intervals can be as short as a few seconds when I pause a movie and when I un-pause the movie, the sound is gone.

I did find a good workaround and that is to play an MP3 continuously in a loop using quicktime and turning the volume down to almost nothing. This seems to keep the HDMI speaker output locked throughout the whole time that I'm using the computer. Thus I always get sound from whatever I happen to wander into, such as a movie on Facebook, a webpage, youtube; otherwise it is a hit or miss situation and sometimes I don't know if the movie clip doesn't have sound or it was just my device that had suddenly decided to turn sound off.

I have searched the web for HDMI sound output, HDMI sound problems to no avail.

Remember this is different from HDMI No Sound as I do get sound through HDMI but after a given interval sometimes just pausing a movie, the sound is gone when un-paused. Yes, when sound is gone, it is gone from everything, including iTunes, quicktime, youtube and toggling output on system preference will toggle it to the internal speakers but will not toggle it back to HDMI even if does say HDMI but I get no sound.

Thanks for reading.