core audio introduction

Core audio provides software interfaces for implementing audio features in applications for iOS and Mac OS X.  

 

In iOS, core audio capabilities include recording, playback, sound effects, positioning, format conversion, file stream parsing, a built-in equalizer and mixer, automatic access to audio input and output hardware, API to manage the audio aspects in the context of a device that can take phone calls, optimizations to extend battery life. 

In iOS, you can use core audio interfaces within Cocoa Touch applications, which are based on the Objective-C language. 

In Mac OS X, core audio capablities include recording, editing, playback, compression and decompression, MIDI, signal processing, file stream parsing, and audio synthesis. 

In Mac OS X, you can use core audio interfaces within a C, Objective-C, or C++ application. 

Note: Core Audio does not provide direct support for audio digital rights management (DRM).

 

     Figure 1-1  Mac OS X Core Audio architecture 

 

 

You find Core Audio application-level services in the Audio Toolbox and Audio Unit frameworks.

• Use Audio Queue Services to record, play back, pause, loop, and synchronize audio.

• Use Audio File, Converter, and Codec Services to read and write from disk and to perform audio data format transformations. In Mac OS X you can also create custom codecs.

• Use Audio Unit Services and Audio Processing Graph Services (represented in the figure as “Audio units”) to host audio units (audio plug-ins) in your application. In Mac OS X you can also create custom audio units to use in your application or to provide for use in other applications.

• Use Music Sequencing Services to play MIDI-based control and music data.

• Use Core Audio Clock Services for audio and MIDI synchronization and time format management.

• Use System Sound Services (represented in the figure as “System sounds”) to play system sounds and user-interface sound effects.

 Figure 1-2  iOS Core Audio architecture 

 

Core Audio in iOS is optimized for the computing resources available in a battery-powered mobile platform. There is no API for services that must be managed very tightly by the operating system—specifically, the HAL and the I/O Kit. However, there are additional services in iOS not present in Mac OS X. For example, Audio Session Services lets you manage the audio behavior of your application in the context of a device that functions as a mobile telephone and an iPod.