Core Audio is the digital audio infrastructure of iOS and OS X. It includes a set of software frameworks designed to handle the audio needs in your applications. Core Audio is tightly integrated into iOS and OS X for high performance and low latency.
In OS X, the majority of Core Audio services are layered on top of the Hardware Abstraction Layer (HAL) as shown in below figure. Audio signals pass to and from hardware through the HAL. You can access the HAL using Audio Hardware Services in the Core Audio framework when you require real-time audio. The Core MIDI (Musical Instrument Digital Interface) framework provides similar interfaces for working with MIDI data and devices.
You find Core Audio application-level services in the Audio Toolbox and Audio Unit frameworks.
- Use Audio Queue Services to record, playback, 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 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 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.
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 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.
In the figure, It provides a High-level view of the audio architecture in iOS