4期_AVFoundation-AVAudioFormat

本文了解AVAudioFormat，通过这个类，我们可以读取到音频的采样率，通道数，量化数以及音频的setting等属性

音频格式，可以通过AVAudioFile获取，可以通过初始化AudioStreamBasicDescription得到

@interface AVAudioFormat : NSObject <NSSecureCoding> {
@private
    AudioStreamBasicDescription _asbd;
    AVAudioChannelLayout *_layout;
    AVAudioCommonFormat _commonFormat;
    void * _reserved;
}


/*! @property commonFormat
    @abstract An `AVAudioCommonFormat` identifying the format
    ？
*/
@property (nonatomic, readonly) AVAudioCommonFormat commonFormat;

/*! @property channelCount
    @abstract The number of channels of audio data.
    音频数据的通道数
*/
@property (nonatomic, readonly) AVAudioChannelCount channelCount;

/*! @property sampleRate
    @abstract A sampling rate in Hertz.
    以赫兹为单位的采样率
*/
@property (nonatomic, readonly) double sampleRate;

/*! @property streamDescription
    @abstract Returns the AudioStreamBasicDescription, for use with lower-level audio API's.
    较为低级的api，底层结构体
*/
@property (nonatomic, readonly) const AudioStreamBasicDescription *streamDescription;

/*! @property settings
    @abstract Returns the format represented as a dictionary with keys from AVAudioSettings.h.
    返回表示为带有AVAudioSettings.h中的键的字典的格式
*/
@property (nonatomic, readonly) NSDictionary<NSString *, id> *settings;
@end

/*! @property channelLayout
    @abstract The underlying AVAudioChannelLayout, if any.
    @discussion
        Only formats with more than 2 channels are required to have channel layouts.
    只有两个通道的音频才有此属性
*/
@property (nonatomic, readonly, nullable) AVAudioChannelLayout *channelLayout;

AVAudioCommonFormat

/*! 
    @enum       AVAudioCommonFormat
    @constant   AVAudioOtherFormat
                    A format other than one of the common ones below.
    @constant   AVAudioPCMFormatFloat32
                    Native-endian floats (this is the standard format).
    @constant   AVAudioPCMFormatFloat64
                    Native-endian doubles.
    @constant   AVAudioPCMFormatInt16
                    Signed 16-bit native-endian integers.
    @constant   AVAudioPCMFormatInt32
                    Signed 32-bit native-endian integers.
*/c
typedef NS_ENUM(NSUInteger, AVAudioCommonFormat) {
    AVAudioOtherFormat = 0,
    AVAudioPCMFormatFloat32 = 1,
    AVAudioPCMFormatFloat64 = 2,
    AVAudioPCMFormatInt16 = 3,
    AVAudioPCMFormatInt32 = 4
} NS_ENUM_AVAILABLE(10_10, 8_0);