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flexaudio

Flexible, cross-platform audio capture for Rust. Capture from microphones, system output (loopback), individual processes, and microphone + system mix on Linux, Windows, and macOS through one unified API.

use flexaudio::{open, StreamConfig, SourceKind};

let mut stream = open(StreamConfig {
    kind: SourceKind::Mic,
    ..Default::default()
})?;
stream.start()?;
while let Some(chunk) = stream.poll_chunk() {
    let _ = chunk; // interleaved f32, plus frames / peak / rms / seq
}
stream.stop();
# Ok::<(), flexaudio::Error>(())

Capability matrix

Source	Linux	Windows	macOS
Microphone	✅ cpal/ALSA	✅ cpal/WASAPI	✅ cpal/CoreAudio
System output	✅ PipeWire	✅ WASAPI loopback	✅ CoreAudio taps
Per-process	✅ PipeWire	✅ WASAPI process	✅ CoreAudio taps

Highlights

open(StreamConfig) selects the right backend by source + OS.
Stream::poll_chunk / poll_event — simple pull loop; no callbacks required.
Stream::switch_source — hot-swap source without stopping the stream.
devices() enumerates devices; watch_devices() reports hotplug notifications on Linux via PipeWire. Windows/macOS return a no-op watcher.
processes() lists audio output session/stream owners on Linux/Windows and Core Audio processes on macOS, including input-only processes. Idle/stopped processes are included and the caller is excluded; use pid as target_pid for capture and is_output_active to check current playback.
SourceKind::Mix combines mic + system audio. Select each side with mix_mic_device_id / mix_system_device_id (None uses defaults), and set mix_mic_gain / mix_system_gain before mixing; gain applies afterward. device_id is ignored for Mix.
exclude_pids combines with exclude_self for system capture and the system side of Mix. Windows excludes one process-tree root (self when exclude_self is true, otherwise the first PID); every entry must equal that root, and distinct PIDs are rejected. macOS resolves audio objects once at start and honors device selection. Linux matches exact PIDs (application.process.id for pulse-proxied streams, pipewire.sec.pid for native clients), without descendants. Linux and Windows ignore system-device selection during exclusion.
Output is normalized interleaved f32 at a sample rate / channel count you choose (two-stage resampling internally).

Install

cargo add flexaudio@0.3

Permissions

Audio capture requires user consent: macOS TCC (kTCCServiceAudioCapture, add NSAudioCaptureUsageDescription to Info.plist), the Windows Microphone privacy setting, and a running PipeWire session on Linux for system/process capture. See the workspace README.

On macOS, system/process loopback (Core Audio process taps) requires macOS 14.4 or later.

MSRV

Rust 1.85.