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Audio Stream Basic Description

AudioStreamBasicDescription

Contains all the information needed for describing streams of audio data.

typedef struct AudioStreamBasicDescription {
Float64 mSampleRate;
UInt32 mFormatID;
UInt32 mFormatFlags;
UInt32 mBytesPerPacket;
UInt32 mFramesPerPacket;
UInt32 mBytesPerFrame;
UInt32 mChannelsPerFrame;
UInt32 mBitsPerChannel;
UInt32 mReserved;
} AudioStreamBasicDescription;

Discussion

The AudioStreamBasicDescription is the fundamental descriptive structure in Core Audio. The “Audio Format” API deals extensively with AudioStreamBasicDescription, as do most other parts of Core Audio.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

In this section:

Format IDs
Format Flags

Format IDs

These values reflect various audio formats available from within Core Audio, and are used to populate the mFormatID field in AudioStreamBasicDescription instances.

kAudioFormatLinearPCM = 'lpcm'

kAudioFormatAC3 = 'ac-3'

kAudioFormat60958AC3 ='cac3'

kAudioFormatMPEG = 'mpeg'

kAudioFormatAppleIMA4 = 'ima4'

kAudioFormatMPEG4AAC = 'aac '

kAudioFormatMPEG4CELP = 'celp'

kAudioFormatMPEG4HVXC = 'hvxc'

kAudioFormatMPEG4TwinVQ = 'twvq'

kAudioFormatTimeCode = 'time'

kAudioFormatMIDIStream = 'midi'

kAudioFormatParameterValueStream = 'apvs'

Format Flags

These values are used to fill the mFormatFlags field of an AudioStreamBasicDescription, and reflect the formatting of the audio stream data.

Standard flags:

kAudioFormatFlagIsFloat = (1L << 0)

kAudioFormatFlagIsBigEndian = (1L << 1)

kAudioFormatFlagIsSignedInteger = (1L << 2)

kAudioFormatFlagIsPacked = (1L << 3)

kAudioFormatFlagIsAlignedHigh = (1L << 4)

kAudioFormatFlagIsNonInterleaved = (1L << 5)

kAudioFormatFlagsAreAllClear = (1L << 31)

Linear PCM flags:

kLinearPCMFormatFlagIsFloat = kAudioFormatFlagIsFloat

kLinearPCMFormatFlagIsBigEndian = kAudioFormatFlagIsBigEndian

kLinearPCMFormatFlagIsSignedInteger = kAudioFormatFlagIsSignedInteger

kLinearPCMFormatFlagIsPacked = kAudioFormatFlagIsPacked

kLinearPCMFormatFlagIsAlignedHigh = kAudioFormatFlagIsAlignedHigh

kLinearPCMFormatFlagIsNonInterleaved = kAudioFormatFlagIsNonInterleaved

kLinearPCMFormatFlagsAreAllClear = kAudioFormatFlagsAreAllClear

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