rill-io 0.5.0-beta.7

Audio I/O backends for Rill - CPAL, ALSA, PipeWire, JACK
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rill-io

Audio I/O backends — PortAudio, ALSA, PipeWire, JACK.

This crate provides I/O backends and the Output/Input graph nodes that own the reactive stream (process callback or similar).

I/O is split into three orthogonal traits:

  • IoDriver — set_process_callback, run, stop (owns the timing loop)
  • IoCapture — read_input(channel, &mut [f32]), num_input_channels()
  • IoPlayback — write_output(channel, &[f32]), num_output_channels()

A single backend struct (e.g. PipewireBackend) implements IoDriver and optionally IoCapture / IoPlayback. IoBackend is a backward-compatible alias: pub trait IoBackend: IoDriver {}.

The process callback is registered via IoDriver::set_process_callback().

Nodes

  • Output — Sink node. Holds Arc<dyn IoPlayback> and calls write_output() directly in consume(). The backend is injected via Sink::set_playback() by ProcessingState::wire_backends().

    let playback: Arc<dyn IoPlayback> = ...;
let mut output = Output::<f32, 256>::with_channels(playback, 2);

  • Input — Source node (push model). Holds Arc<dyn IoCapture>. Same pattern — Source::set_capture() injects the backend.

The process callback (registered by the orchestrator) does:

  1. Drain actor mailbox (SetParameter commands) into graph nodes
  2. ProcessingState::process_block(&tick) — generates, processes, propagates
  3. ProcessingState::send_clock_tick(&tick) — dispatches to control actors

Backends

Backend Feature Thread model
PortAudioBackend portaudio (default) RT callback, exact buffer size
PipewireBackend pipewire RT callback (PW thread)
JackBackend jack RT callback (JACK thread)
AlsaBackend alsa snd_pcm_wait() — poll‑driven, exact period required
NullBackend (always) No‑op, for testing

Sample rate negotiation:

  • JACK: reads client.sample_rate() after activation
  • ALSA: queries hw.get_rate() after set_rate(Nearest), checks hw.get_period_size() == BUF_SIZE
  • PipeWire: output uses requested rate, input reads negotiated rate atomically
  • PortAudio: opens stream with exact requested rate and buffer size
  • Null: uses config.sample_rate directly

Links