I have a Samsung TV (UA55) which used to work quite well, but suddenly stopped. This article doesn't contain any solutions. It serves to exist as proof that the issue exists.
I tried to search for references to this issue but found that there are no results for the exact string "unknown audio playback error".
So here I am creating the first search result now.
Here's a link to a support thread on the Samsung Community Forums: https://us.community.samsung.com/t5/HD-and-UHD-TVs/YouTube-Music-won-t-play/m-p/1993968
Samsung have not acknowledged the issue and no solution is available at this time.
Samsung deleted the community forum thread without resolving the issue.