Mic crashes when number of channels > 32

[b-ma]

test with blackhole 64ch

[orottier]

It's probably due to the hard limit on the Rust side

/// Maximum number of channels for audio processing
pub const MAX_CHANNELS: usize = 32;

This limit has been put in place so we can keep audio buffers (specifically, the AudioRenderQuantum) fully on the stack and not add some indirection to the heap.
Increasing the limit will hit performance both in CPU and RAM usage. Also what should the new limit be, 64, 256? There is no clean solution there.

Perhaps changing to a SmallVec that keeps buffers up to 32 channels (or less) on the stack and spills to the heap when there is more would be fine. It would have a small CPU usage impact for all users (also the ones with small number of channels). We could benchmark this.

Probably we should move this issue to https://github.com/orottier/web-audio-api-rs/

[b-ma]

Hey,

Just to explain a bit more (I just threw this to not forget, but it was a bit too laconic :). I didn't try to grab more than 32 channels with the mic, it was just the fact that more input channels were available from the virtual soundcard that made the script crash. I will try to recreate the setup, will be more clear.

For now, I think this would be ok to just clamp to max number of channels.

[orottier]

Alright sure! The actual error message would be useful to have.
In any case I think the discussion in the linked issue is worth having. If I remember correctly, at least Firefox has no limits on the number of channels

[sletz]

AFAICS this number of channels <= 32 is part of the WebAudio API specification itself, where the exact wording for numberOfInputChannels and numberOfOutputChannels to Values of up to 32 must be supported.