Here's a bit more stuff from the same stable that says it relates to ubuntu 16.04:

http://linuxiumcomau.blogspot.com/2018/03/

This should be more appropriate.

I just found some stuff that sounds relevant, but I'm afraid it's a bit over my head. Maybe it may mean more to someone else. See the following link:

http://linuxiumcomau.blogspot.com/2017/10/fixing-broken-hdmi-audio.html

Good luck!

I am disappointed that this bug does not appear to be a priority. My Blackberry Playbook had this feature working years ago. Surely this is a fundamental requirement if we wish to talk about convergence. The comment by @dobey on github implies that if it's not supported by pulse-audio, then it won't get fixed. Surely that's not good enough? What do others think?

@advocatux Many thanks for your support.

I've noticed that System Settings crashes when I select ~/Security & Privacy/App Permissions. This happens on both my M10 tablet and also my Nexus 4 phone. Both of these devices are running xenial rc (UT v. 23). If anyone else can confirm this problem, please can someone skilled in the art log it as an issue. Thanks.

I'm pleased to report that this issue was resolved by replacing my youtube app with the one by Alan Pope. Youtube now runs sweetly on my tablet.

Youtube was working fine with OTA 4 stable on my M10 tablet. Then I installed OTA 5 stable and it now no longer works. If I try to launch it with either the webapp or the browser, the home page appears for an instant and is then replaced by an error message with a request to reload via the gadget at the foot of the page. I tried that and just got the same error message.
BTW, Youtube works fine with OTA 5 rc on my Nexus 4. One thing I've noticed is that the user agent is different between these two devices. I would be interested in your comments please.

Tonight, I discovered that the problem with my tablet with ebay was because for some reason it was displaying the mobile site. Previously the M10 had always displayed the classic site which worked fine on the tablet.
So I looked for a way to switch it back. I found that if I scrolled right to the bottom of the mobile site page, there was tiny clickable classic site emblem.
Clicking that control immediately switched the display back to classic mode and everything worked smoothly without any insecure connection messages.
In any case, on the tablet, classic mode is superior as more information is displayed.
I hope this information will be helpful for other M10 tablet users.

Seems to be fixed now: 49.8-2.1=47.7! 👍