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Audio Family Design

All audio drivers, regardless of platform, must perform the same general actions. For input streams, drivers receive digital audio data from the hardware in a stream of frames consistent with the current sampling rate and audio format. They modify the data, if necessary, to a form acceptable to the clients of the device (say, 32-bit floating point) and make the altered frames accessible to those clients at the current sampling rate. In the reverse (output) direction, the job of the audio driver is essentially the same. It accepts digital audio data from the clients of the device, changes that stream of sample frames to a form required by the hardware (say, 16-bit integer), and gives the data to the device’s controller at the current sampling rate.

Drivers must also initially configure the hardware, respond to client requests to change device attributes (for example, volume), and notify clients when some attribute or state of the audio device has changed. They must guard against data corruption in a multithreaded environment, and they must be prepared to respond to systemwide events, such as sleep/wake notifications.

The Audio family provides object-oriented abstractions to help your driver deal with many of these things. The family itself takes care of much of the work for you; you just supply the behavior that is specific to your hardware. To do this, it is useful to know how your code fits together with the family implementation, which is what this chapter is about.

Contents:

The Classes of the Audio Family
The Audio I/O Model Up Close
Interfaces With the Audio HAL

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