If you're interested in HDMI audio, I have code for that lying around. The current best Rust source is in [1], but I also have a local branch with hand-tuned asm for the terc4 encoding. It's maybe 25% faster, which might be significant, as the per-scanline CPU load does go up a fair amount.

[1]: https://github.com/DusterTheFirst/pico-dvi-rs/blob/main/src/...