Hardware Reference
In-Depth Information
DirectX and Audio Support Hardware
Microsoft DirectX is a series of application programming interfaces (APIs) that sits between
multimedia applications and hardware. Unlike MS-DOS applications, which required developers to
develop direct hardware support for numerous models and brands of audio cards, video cards, and
game controllers, Windows applications use DirectX to “talk” to hardware in a more direct manner
than normal Windows drivers do. This improves program performance and frees the software
developer from the need to change the program to work with different devices. Instead, a game
developer must work with only the DirectX 3D renderer and other DirectX interface routines. Until
the introduction of DirectX 10 with Windows Vista, audio programming was also part of DirectX.
For more information about DirectX, see the
Chapter 12
section, “
Microsoft DirectX
,”
p.
646
.
Core Audio APIs for Windows
Although Windows Vista's changes to the desktop are well known, an equally significant change in
Windows Vista is how it works with audio. DirectX 10, the native version of DirectX included in
Windows Vista, no longer includes audio APIs such as DirectSound and DirectMusic. These and
other audio-oriented APIs now interface with Windows via the new Core Audio APIs originally
introduced in Windows Vista (see
http://msdn.microsoft.com/en-us/library/dd370784(v=vs.85).aspx
)
and improved in Windows 7 and Windows 8. These APIs include:
•
Multimedia Devices (MMDevice) API
—Clients use MMDevice to enumerate the audio
endpoint devices in the system.
•
Windows Audio Session API (WASAPI)
—Clients use WASAPI to create and manage audio
streams coming to or from audio endpoint devices.
•
DeviceTopology API
—Clients use DeviceTopology API for direct access to features such as
volume controls and multiplexers along the data paths of hardware devices inside audio
adapters.
•
EndpointVolume API
—Clients use the EndpointVolume API for direct access to volume
controls on audio endpoint devices. It is primarily used for the management of exclusive-mode
audio streams.
Some types of applications, such as media players, DVD players and BD media players, games, and
business applications that play sound files, such as presentation programs, connect to Core Audio
APIs via the higher-level APIs such as DirectSound or Media Foundation. However, professional
audio and real-time communications applications and third-party audio APIs typically access Core
Audio APIs directly.
Note
An audio endpoint device is a device such as a speaker, microphone, or other audio input
device such as Line In, volume controls, or analog-to-digital converters such as a Wave input
us/library/dd370793(v=vs.85).aspx
.
Windows 7 uses improved versions of the Core Audio APIs to provide low-latency audio streams,
playback of audio from portable media devices through your computer speakers, improved HDMI
