PyAudioCast

Cross-platform audio output library for Python, powered by Rust and CPAL.

Stream audio to any output device — including PipeWire/PulseAudio virtual sinks on Linux — with a simple Python API backed by a high-performance Rust core.

Features

• Cross-platform: Linux (ALSA/PipeWire/PulseAudio), Windows (WASAPI), macOS (CoreAudio)
• Auto-detect: Sample rate and channels are detected from the device — zero config needed
• Auto-negotiate: If the device doesn't support your sample rate, it automatically resamples and upmixes (e.g. 22050Hz mono TTS → 48000Hz stereo device)
• Device selection: List and select output devices by name, including PipeWire virtual sinks
• Streaming audio: Write audio data in chunks via a lock-free ring buffer — ideal for real-time TTS, generative audio, live effects, etc.
• Unified write(): Accepts bytes, numpy arrays (int16/int32/float32/float64), or list[float] — format is detected automatically
• Interruption: clear() instantly discards buffered audio and unblocks drain() — perfect for voice assistant barge-in
• Context manager: Clean resource management with with statement
• GIL-friendly: Releases the Python GIL during audio writes and drain, so other threads run freely
• Clean output: ALSA/JACK backend probe noise is automatically suppressed
• Debug logging: Enable detailed logs with PYAUDIOCAST_LOG=debug

Installation

From PyPI

pip install pyaudiocast

Note (Linux): Pre-built wheels require ALSA. Install libasound2 if not already present:

sudo apt install libasound2  # Debian/Ubuntu
sudo dnf install alsa-lib    # Fedora

From source (requires Rust toolchain)

# Install Rust if needed
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

# Linux: install ALSA development headers
sudo apt install libasound2-dev  # Debian/Ubuntu
sudo dnf install alsa-lib-devel  # Fedora

# Clone and install
git clone https://github.com/nicokim/PyAudioCast.git
cd PyAudioCast
pip install maturin
maturin develop

Development setup (with uv)

uv venv && source .venv/bin/activate
uv pip install maturin numpy pytest
maturin develop

Quick Start

import pyaudiocast

# List all output devices
for dev in pyaudiocast.list_output_devices():
    print(f"[{dev['index']}] {dev['name']} ({dev['type']})")

# Stream audio — sample rate and channels auto-detected from device
with pyaudiocast.AudioPlayer() as player:
    print(f"Using: {player.sample_rate}Hz, {player.channels}ch")
    player.write(audio_bytes)   # bytes, numpy array, or list[float]
    player.drain()              # wait for playback to finish

# Override sample rate if your source requires it (auto-resampled to device)
with pyaudiocast.AudioPlayer(sample_rate=22050) as player:
    player.write(tts_audio)
    player.drain()

# Stream to a specific device
with pyaudiocast.AudioPlayer(device="Virtual-Mic") as player:
    player.write(samples)
    player.drain()

# One-shot WAV playback
pyaudiocast.play_file("audio.wav", device="pulse")

Streaming with Interruption

For real-time applications like voice assistants, you can interrupt playback instantly:

import pyaudiocast
import threading

with pyaudiocast.AudioPlayer(sample_rate=22050) as player:
    # Stream TTS chunks as they arrive
    for chunk in tts_stream:
        player.write(chunk)
    player.drain()  # wait for playback to finish

# Interrupt from another thread (e.g., when user starts speaking)
def on_user_speech_detected(player):
    player.clear()  # instantly stops audio, unblocks drain()

clear() discards all buffered audio immediately. Any blocked drain() returns right away. Calling write() again resumes normal playback.

Supported Audio Formats

write() auto-detects the input format:

Input type	Format	Conversion
bytes	int16 little-endian PCM	Converted to float32
numpy.ndarray (int16)	int16 samples	Converted to float32
numpy.ndarray (int32)	int32 samples	Converted to float32
numpy.ndarray (float32)	float32 samples	Direct (no conversion)
numpy.ndarray (float64)	float64 samples	Converted to float32
list[float]	float32 samples (-1.0 to 1.0)	Direct

import numpy as np

with pyaudiocast.AudioPlayer() as player:
    # All of these work with the same write() method
    player.write(b"\x00\x00" * 100)                    # bytes (int16 LE)
    player.write(np.zeros(100, dtype=np.int16))         # numpy int16
    player.write(np.zeros(100, dtype=np.float32))       # numpy float32 (fastest)
    player.write(np.zeros(100, dtype=np.float64))       # numpy float64
    player.write(np.zeros(100, dtype=np.int32))         # numpy int32
    player.write([0.0] * 100)                           # list[float]

API Reference

pyaudiocast.list_output_devices() -> list[dict]

Returns a list of available output devices. Each dict contains:

• name (str): Device name
• index (int): Device index
• type (str): "alsa" for ALSA/cpal devices, "pipewire" for PipeWire/PulseAudio sinks

pyaudiocast.AudioPlayer(device=None, sample_rate=None, channels=None)

Streaming audio player with ring buffer.

Parameter	Type	Default	Description
device	str | None	None	Device name (substring match) or None for default
sample_rate	int | None	None	Sample rate in Hz, or None to auto-detect
channels	int | None	None	Number of audio channels, or None to auto-detect

If sample_rate or channels don't match the device natively, pyaudiocast automatically resamples and/or upmixes to the device's supported configuration.

Methods:

Method	Description
write(data)	Write audio data (bytes, numpy array, or list[float])
drain()	Block until all buffered audio is played
clear()	Discard buffer and unblock drain() immediately
stop()	Stop playback and release resources

Properties:

Property	Type	Description
sample_rate	int	Requested sample rate (what you send)
channels	int	Requested channel count (what you send)
device_sample_rate	int	Actual device sample rate (what plays)
device_channels	int	Actual device channel count (what plays)
is_active	bool	Whether the player is active

Context manager: Supports with statement (calls stop() on exit).

pyaudiocast.play_file(path, device=None)

Play a WAV file to completion. Blocks until playback is done.

Device Selection

Default device

player = pyaudiocast.AudioPlayer()  # uses system default

ALSA device (by name substring)

player = pyaudiocast.AudioPlayer(device="pulse")
player = pyaudiocast.AudioPlayer(device="hw:CARD=Audio")

PipeWire/PulseAudio virtual sinks (Linux)

# Virtual sinks are auto-detected via pactl
player = pyaudiocast.AudioPlayer(device="Virtual-Mic")

PipeWire sinks are routed transparently through PULSE_SINK + the pulse ALSA device.

Environment Variables

Variable	Description	Example
PYAUDIOCAST_LOG	Enable debug logging. Uses env_logger filter syntax.	PYAUDIOCAST_LOG=debug

Logging

# Show everything (including ALSA/JACK backend messages)
PYAUDIOCAST_LOG=debug python my_script.py

# Show info and above
PYAUDIOCAST_LOG=info python my_script.py

# Default (no env var): warnings only, ALSA/JACK noise suppressed
python my_script.py

Cross-Platform Support

Platform	Backend	Device listing	Virtual sinks
Linux	ALSA + PipeWire/Pulse	Full	Yes (via pactl)
Windows	WASAPI	cpal devices	N/A
macOS	CoreAudio	cpal devices	N/A

The audio engine (cpal) is fully cross-platform. PipeWire/PulseAudio virtual sink detection uses pactl and is automatically compiled out on non-Linux systems via #[cfg(target_os = "linux")].

Architecture

Python (pyaudiocast)
  |
  +- write(data)  ->  auto-detect format  ->  convert to f32
  |     |
  |     v
  |  [resample + upmix if needed]
  |     |
  |     v
  |  Lock-free Ring Buffer (ringbuf crate)
  |     |
  |     v
  |  cpal audio callback (OS audio thread)
  |     |                          ^
  |     v                          |
  +- Speaker / Virtual Sink    clear() -> discard + silence

• Ring buffer: Lock-free producer/consumer. Python pushes samples, the OS audio callback pulls them — no locks in the audio path.
• GIL release: write() and drain() release the Python GIL during blocking operations.
• Sample conversion: All input formats are converted to float32 in Rust before entering the ring buffer.
• Auto-resample: If the device doesn't natively support the requested sample rate, linear interpolation resampling is applied transparently.
• Auto-upmix: Mono audio is automatically duplicated to stereo (or more channels) to match the device.
• Interruption: clear() sets an atomic flag checked by the audio callback, which discards remaining samples and outputs silence.

Running Tests

# Python tests
pytest tests/ -v

# Rust tests
cargo test

License

MIT