Roku products seem to be subpar and defective.
I had the same issue which happened only within the first week of purchase from BestBuy. I swapped it and the second unit now has similar audio issues after 4 weeks.
Roku CS are non-supportive.
Both are Roku Ultra units BTW..
I am looking for a Roku alternative now.
When I say the codec doesn't matter, I mean I've tried converting to several that are suppose to be supported by Roku, various versions of h.264 and MKV. For the audio, usually the file comes as AAC (core audio). Handbrake offers HE-AAC, AAC Passthru, AC3, MP3 and Audio Passthru. I have only tried converting to Audio Passthru. Please explain how to set it up to use the TV audio.
I have an update on audio.
It doesn't seem to be device related but firmware.
Although my first R.U. had no sound (until reset), the second one dropped volume by more than 50% (until reset).
So I have a replacement Roku Ultra (my third in two months) and it does the same thing. It happened again just now.
I think this points the way to an issue with firmware on R.U. and not the devices themselves.