audio File Stream Services关键数据结构

struct AudioStreamBasicDescription {
   Float64 mSampleRate;	//每秒播放的fram数目；
   UInt32  mFormatID;	//audio file 数据标志非零
   UInt32  mFormatFlags;//
   UInt32  mBytesPerPacket;	//一个packet中的字节数目，如果时可变的packet则为0；
   UInt32  mFramesPerPacket;	//packet中包含的frame数目，无压缩时为1，可变比特率时，一个达点儿的固定值例如在ACC中1024。
   UInt32  mBytesPerFrame;	//
   UInt32  mChannelsPerFrame;	//frame中包含的channel数目
   UInt32  mBitsPerChannel;	//The number of bits for one audio sample. 
   UInt32  mReserved;	//保留
};
typedef struct AudioStreamBasicDescription  AudioStreamBasicDescription;

struct AudioStreamPacketDescription {
   SInt64  mStartOffset;
   UInt32  mVariableFramesInPacket;
   UInt32  mDataByteSize;
};
typedef struct AudioStreamPacketDescription AudioStreamPacketDescription;

Constants
Sample Type Constants
#define kAudioUnitSampleFractionBits 24
Audio Data Format Identifiers
enum {
   kAudioFormatLinearPCM               = 'lpcm',
   kAudioFormatAC3                     = 'ac-3',
   kAudioFormat60958AC3                = 'cac3',
   kAudioFormatAppleIMA4               = 'ima4',
   kAudioFormatMPEG4AAC                = 'aac ',
   kAudioFormatMPEG4CELP               = 'celp',
   kAudioFormatMPEG4HVXC               = 'hvxc',
   kAudioFormatMPEG4TwinVQ             = 'twvq',
   kAudioFormatMACE3                   = 'MAC3',
   kAudioFormatMACE6                   = 'MAC6',
   kAudioFormatULaw                    = 'ulaw',
   kAudioFormatALaw                    = 'alaw',
   kAudioFormatQDesign                 = 'QDMC',
   kAudioFormatQDesign2                = 'QDM2',
   kAudioFormatQUALCOMM                = 'Qclp',
   kAudioFormatMPEGLayer1              = '.mp1',
   kAudioFormatMPEGLayer2              = '.mp2',
   kAudioFormatMPEGLayer3              = '.mp3',
   kAudioFormatTimeCode                = 'time',
   kAudioFormatMIDIStream              = 'midi',
   kAudioFormatParameterValueStream    = 'apvs',
   kAudioFormatAppleLossless           = 'alac'
   kAudioFormatMPEG4AAC_HE             = 'aach',
   kAudioFormatMPEG4AAC_LD             = 'aacl',
   kAudioFormatMPEG4AAC_ELD            = 'aace',
   kAudioFormatMPEG4AAC_HE_V2          = 'aacp',
   kAudioFormatMPEG4AAC_Spatial        = 'aacs',
   kAudioFormatAMR                     = 'samr',
   kAudioFormatAudible                 = 'AUDB',
   kAudioFormatiLBC                    = 'ilbc',
   kAudioFormatDVIIntelIMA             = 0x6D730011,
   kAudioFormatMicrosoftGSM            = 0x6D730031,
   kAudioFormatAES3                    = 'aes3'
};
AudioStreamBasicDescription Flags
enum {
   kAudioFormatFlagIsFloat                  = (1 << 0),    // 0x1
   kAudioFormatFlagIsBigEndian              = (1 << 1),    // 0x2
   kAudioFormatFlagIsSignedInteger          = (1 << 2),    // 0x4
   kAudioFormatFlagIsPacked                 = (1 << 3),    // 0x8
   kAudioFormatFlagIsAlignedHigh            = (1 << 4),    // 0x10
   kAudioFormatFlagIsNonInterleaved         = (1 << 5),    // 0x20
   kAudioFormatFlagIsNonMixable             = (1 << 6),    // 0x40
   kAudioFormatFlagsAreAllClear             = (1 << 31),
   
   kLinearPCMFormatFlagIsFloat              = kAudioFormatFlagIsFloat,
   kLinearPCMFormatFlagIsBigEndian          = kAudioFormatFlagIsBigEndian,
   kLinearPCMFormatFlagIsSignedInteger      = kAudioFormatFlagIsSignedInteger,
   kLinearPCMFormatFlagIsPacked             = kAudioFormatFlagIsPacked,
   kLinearPCMFormatFlagIsAlignedHigh        = kAudioFormatFlagIsAlignedHigh,
   kLinearPCMFormatFlagIsNonInterleaved     = kAudioFormatFlagIsNonInterleaved,
   kLinearPCMFormatFlagIsNonMixable         = kAudioFormatFlagIsNonMixable,
   kLinearPCMFormatFlagsSampleFractionShift = 7,
   kLinearPCMFormatFlagsSampleFractionMask  =
   (0x3F << kLinearPCMFormatFlagsSampleFractionShift),
   kLinearPCMFormatFlagsAreAllClear         = kAudioFormatFlagsAreAllClear,
   
   kAppleLosslessFormatFlag_16BitSourceData = 1,
   kAppleLosslessFormatFlag_20BitSourceData = 2,
   kAppleLosslessFormatFlag_24BitSourceData = 3,
   kAppleLosslessFormatFlag_32BitSourceData = 4
};
AudioStreamBasicDescription Flag Combinations Constants
enum {
#if TARGET_RT_BIG_ENDIAN
   kAudioFormatFlagsNativeEndian       = kAudioFormatFlagIsBigEndian,
#else
   kAudioFormatFlagsNativeEndian       = 0,
#endif
   
#if !CA_PREFER_FIXED_POINT
   kAudioFormatFlagsCanonical          =   kAudioFormatFlagIsFloat |
   kAudioFormatFlagsNativeEndian |
   kAudioFormatFlagIsPacked,
   kAudioFormatFlagsAudioUnitCanonical =   kAudioFormatFlagIsFloat |
   kAudioFormatFlagsNativeEndian |
   kAudioFormatFlagIsPacked |
   kAudioFormatFlagIsNonInterleaved,
#else
   kAudioFormatFlagsCanonical          =   kAudioFormatFlagIsSignedInteger |
   kAudioFormatFlagsNativeEndian |
   kAudioFormatFlagIsPacked,
   kAudioFormatFlagsAudioUnitCanonical =   kAudioFormatFlagIsSignedInteger |
   kAudioFormatFlagsNativeEndian |
   kAudioFormatFlagIsPacked |
   kAudioFormatFlagIsNonInterleaved |
   (kAudioUnitSampleFractionBits <<
   kLinearPCMFormatFlagsSampleFractionShift),
   
#endif
   
   kAudioFormatFlagsNativeFloatPacked  =   kAudioFormatFlagIsFloat |
   kAudioFormatFlagsNativeEndian |
   kAudioFormatFlagIsPacked
};
AudioSampleType
The canonical audio data sample type for input and output.
typedef SInt16 AudioSampleType;
AudioUnitSampleType
The canonical audio data sample type for audio processing.
typedef SInt32 AudioUnitSampleType;
#define kAudioUnitSampleFractionBits 24