HomePod audio output when paired with tvOS is unreliable when watching in Channels.
Background
Channels uses its own custom video player. This allows it to play back codecs and video containers directly that would otherwise have to be transcoded/remuxed to play in the tvOS/iOS system video player, which only supports h.264 and h.265 with very limited container support.
The custom player also allows for many of the features you see in Channels and is not something that will change any time soon.
Many other media players (Plex, Emby, Jellyfin, and VLC) with custom players exhibit the same issues and all struggle to play back on HomePods correctly.
Our Efforts
HomePod output is something that is completely private to tvOS and we have no real interaction code wise.
We have spent many hours across many years making this better and have made some accomplishments. Though with each major update, Apple changes how HomePods work with tvOS, and there is no real documentation on this. It's all just magic and a big secret.
We have found and submitted bug reports for issues blocking better support. Apple has acknowledged them, though they have not implemented any changes to solve them.
Known Variables
Channels + Apple TV without HomePod pairing works totally fine.
Using PIP seems to make it worse, we suggest just not using PIP if you have paired HomePods.
Work Arounds
None at the moment.
Old Topics
Current Status
With the tvOS 17 update, HomePod support has gone from ok, to not very reliable again. Work will have to be done yet again to make changes to work with tvOS 17.