PortAudio Audio I/O Library

PortAudio is a free, cross-platform, open-source audio I/O library that provides a uniform API for recording and playing sound across multiple platforms. Originally developed by Phil Burk and Ross Bencina, PortAudio has become the standard portable audio library since 2000. Key features: unified C API for audio input and output supporting blocking (read/write) and callback-based audio processing paradigms. Cross-platform support on Windows (WASAPI, DirectSound, ASIO, WDM-KS), macOS (CoreAudio), Linux (ALSA, JACK, PulseAudio, OSS), and other Unix systems. Multiple host APIs selectable at runtime, enabling ASIO for low-latency professional audio on Windows or CoreAudio on macOS. Callback architecture with real-time audio processing via user-provided callback function called at audio interrupt level for zero-latency processing. Blocking I/O mode via read/write functions for simpler programming models and integration with non-real-time code. Sample format support including 8/16/24/32-bit integer, 32-bit float, and custom formats with automatic conversion. Adjustable buffer sizes and latency settings from sub-millisecond (ASIO) to high-latency for stable playback. Full-duplex (simultaneous record and play) and half-duplex operation. Multiple device support with device enumeration, channel count, and sample rate queries. Stream time tracking and synchronization for sample-accurate timing. Thread-safe API for multi-threaded applications. Used by Audacity, JACK, SDL, SFML, and hundreds of audio applications. Bindings available for Python (sounddevice, pyaudio), Ruby, Haskell, and more.