moq-audio 0.1.8

Native audio encoding/decoding for Media over QUIC
Documentation 
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//! A stand-in AAC encoder, so the AAC front end is testable on a host with no
//! platform encoder. A test opts in with [`install`]; every other test sees the
//! real tiers.

use std::cell::Cell;

use bytes::Bytes;

use super::Backend;
use crate::Error;
use crate::encode::{Encoded, Settings};

pub(crate) const NAME: &str = "stub";

/// The AudioToolbox AAC-LC encoder delay, which is what a real backend reports.
pub(crate) const DELAY: usize = 2112;

thread_local! {
	static INSTALLED: Cell<bool> = const { Cell::new(false) };
}

/// Stand the stub in for the platform tier on this thread until the guard drops.
pub(crate) fn install() -> Installed {
	INSTALLED.set(true);
	Installed(())
}

/// Whether this thread has the stub installed.
pub(super) fn installed() -> bool {
	INSTALLED.get()
}

/// Uninstalls the stub on drop.
pub(crate) struct Installed(());

impl Drop for Installed {
	fn drop(&mut self) {
		INSTALLED.set(false);
	}
}

/// Emits each frame's index as its payload, and cannot retune.
pub(crate) struct Stub {
	bitrate: u64,
	frames: u64,
}

impl Stub {
	pub(super) fn open(settings: &Settings) -> Result<Box<dyn Backend>, Error> {
		Ok(Box::new(Self {
			bitrate: settings.bitrate.map_or(128_000, |rate| rate.as_bps()),
			frames: 0,
		}))
	}
}

impl Backend for Stub {
	fn encode(&mut self, _pcm: &[f32]) -> Result<Encoded, Error> {
		let payload = Bytes::copy_from_slice(&self.frames.to_be_bytes());
		self.frames += 1;
		Ok(Encoded::new(payload))
	}

	fn reset(&mut self) {
		self.frames = 0;
	}

	fn set_bitrate(&mut self, bitrate: u64) -> Result<(), Error> {
		match bitrate == self.bitrate {
			true => Ok(()),
			false => Err(Error::Unsupported("the stub cannot change rate mid-stream".into())),
		}
	}

	fn bitrate(&self) -> u64 {
		self.bitrate
	}

	fn delay(&self) -> usize {
		DELAY
	}

	fn name(&self) -> &str {
		NAME
	}
}