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| WASAPI | |
|---|---|
| Name | WASAPI |
| Developer | Microsoft |
| Released | 2007 |
| Latest release | Windows Vista and later |
| Platform | Windows |
| License | Proprietary |
WASAPI
WASAPI is a low-level audio API introduced by Microsoft for Windows audio pipeline control. It provides client applications with access to audio endpoints and supports shared and exclusive modes for rendering and capturing audio. The interface is integral to modern multimedia stacks and interacts with kernel-mode drivers and user-mode clients.
WASAPI operates within the Windows multimedia ecosystem alongside DirectSound, MME, Core Audio APIs, Media Foundation, and Windows Driver Model components. Designed for professional audio and consumer scenarios, WASAPI interfaces with endpoint devices managed by Windows Audio, Audio Session API, Kernel Streaming, and the Windows Vista audio architecture introduced during the development of Longhorn. Its design addresses needs from digital audio workstations used by artists associated with Ableton Live and Pro Tools workflows to playback engines in applications like VLC media player and foobar2000.
WASAPI's architecture connects user-mode clients to kernel-mode audio drivers via the Windows Audio Session API, IMSClient, and endpoint enumeration provided by Device Manager and Plug and Play. The model differentiates between endpoint devices such as USB audio devices from vendors like Focusrite and M-Audio and integrated chipsets from Realtek. It leverages concepts from COM and uses interfaces influenced by DirectX and Windows Runtime patterns. The architecture interacts with policy and session components from Windows Audio Service and coordinates timing with scheduler facilities like Windows Timer and High Precision Event Timer.
WASAPI supports multiple stream types, including render and capture streams used by players like Winamp and recorders such as Audacity. It exposes two principal modes: shared mode, where the system mixer handled by Audio Engine performs format conversion and resampling similar to components in Media Foundation Transforms, and exclusive mode, where an application obtains direct access to endpoint hardware akin to ASIO drivers used in professional studios collaborating with manufacturers like Steinberg and Yamaha. Stream formats often involve standards from IEC 60958, IEC 61937, and PCM formats used in Compact Disc production.
WASAPI's performance characteristics are crucial for low-latency scenarios in virtual instruments from Native Instruments and live audio processing in installations by Avid Technology. Exclusive mode minimizes intermediary processing and can achieve hardware-level latencies comparable to ASIO by bypassing the system mixer and reducing buffering. Shared mode introduces mixing latency similar to what is experienced in Windows Media Player and streaming services like Spotify running on Windows. Clock drift and synchronization with external instruments using protocols such as MIDI and timecode standards like SMPTE require careful handling of sample rates and buffer sizes.
Developers use COM interfaces exposed by WASAPI within environments such as Microsoft Visual Studio, leveraging languages like C++, C#, and bridging libraries for Python and Rust. Common interfaces include device enumerators, endpoint volume controls, and render/capture clients accessed via methods comparable to patterns in Win32 API. Sample applications and SDK examples are often distributed with Windows SDK and demonstrated in tutorials at conferences like Microsoft Build and CES sessions. Integration practices reference driver models from Windows Driver Kit and diagnostics from Event Viewer.
WASAPI is supported on Windows versions from Windows Vista onward and integrates with audio subsystems used by commercial DAWs from Steinberg, Avid, and Image-Line. It coexists with legacy APIs such as MME and DirectSound through the system's compatibility layers and can be used alongside multimedia frameworks including GStreamer and FFmpeg when combined with platform-specific backends. Hardware compatibility extends across certified Windows Hardware Certification devices, including professional interfaces by Universal Audio and consumer devices by Intel-based OEMs and Dell and HP systems.
WASAPI participates in Windows security models controlling device access through user session isolation implemented in Session 0 Isolation and permissioning under User Account Control. Access to audio endpoints can be mediated by policies set via Group Policy and by per-application consent mechanisms similar to those managed by Windows Privacy Settings. Driver signing enforced by Kernel Mode Code Signing and kernel-level protections from PatchGuard help ensure integrity of audio drivers, while sandboxed applications in Microsoft Store contexts face additional capability declarations.
Category:Audio software Category:Microsoft APIs Category:Windows APIs