Audio ToolBox 解码

音频解码器

官方文档：https://developer.apple.com/documentation/audiotoolbox/audio_converter_services?language=occ

1.创建音频转换器 AudioConverterNewSpecific

/*!
    @function   AudioConverterNewSpecific
    @abstract   Create a new AudioConverter using specific codecs.

    @param      inSourceFormat
                    The format of the source audio to be converted.
    @param      inDestinationFormat
                    The destination format to which the audio is to be converted.
    @param      inNumberClassDescriptions
                    The number of class descriptions.
    @param      inClassDescriptions
                    AudioClassDescriptions specifiying the codec to instantiate.
    @param      outAudioConverter
                    On successful return, points to a new AudioConverter instance.
    @result     An OSStatus result code.
    
    @discussion
                This function is identical to AudioConverterNew(), except that the client may
                explicitly choose which codec to instantiate if there is more than one choice.
*
extern OSStatus
AudioConverterNewSpecific(  const AudioStreamBasicDescription * inSourceFormat,
                            const AudioStreamBasicDescription * inDestinationFormat,
                            UInt32                              inNumberClassDescriptions,
                            const AudioClassDescription *       inClassDescriptions,
                            AudioConverterRef __nullable * __nonnull outAudioConverter)

例子

//1.音频来源格式
AudioStreamBasicDescription inSourceFormat = {
        .mSampleRate         = 48000,
        .mFormatID           = kAudioFormatMPEG4AAC,
        .mChannelsPerFrame   = 2,
        .mFramesPerPacket    = 1024,
    }; 
//2.要转换成的音频格式     
AudioStreamBasicDescription inDestinationFormat = {0};
inDestinationFormat.mSampleRate = 48000;
inDestinationFormat.mFormatID = kAudioFormatLinearPCM;
inDestinationFormat.mChannelsPerFrame  = 1;
inDestinationFormat.mFormatID          = kAudioFormatLinearPCM;
inDestinationFormat.mFormatFlags       = (kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked);
inDestinationFormat.mFramesPerPacket   = 1;
inDestinationFormat.mBitsPerChannel    = 16;
inDestinationFormat.mBytesPerFrame     = inDestinationFormat.mBitsPerChannel / 8 *inDestinationFormat.mChannelsPerFrame;
inDestinationFormat.mBytesPerPacket    = inDestinationFormat.mBytesPerFrame * inDestinationFormat.mFramesPerPacket;
inDestinationFormat.mReserved          =  0;

//3.创建AudioClassDescription
- (AudioClassDescription *)getAudioCalssDescriptionWithType:(AudioFormatID)type fromManufacture:(uint32_t)manufacture {
    static AudioClassDescription desc;
    UInt32 decoderSpecific = type;
    UInt32 size;
    OSStatus status = AudioFormatGetPropertyInfo(kAudioFormatProperty_Decoders,
                                                 sizeof(decoderSpecific),
                                                 &decoderSpecific,
                                                 &size);
    if (status != noErr) {
        NSLog(@"Error！：硬解码AAC get info 失败, status= %d", (int)status);
        return nil;
    }
    //计算aac解码器的个数
    unsigned int count = size / sizeof(AudioClassDescription);
    //创建一个包含count个解码器的数组
    AudioClassDescription description[count];
    //将满足aac解码的解码器的信息写入数组
    status = AudioFormatGetProperty(kAudioFormatProperty_Decoders,
                                    sizeof(decoderSpecific),
                                    &decoderSpecific,
                                    &size,
                                    &description);
    if (status != noErr) {
        NSLog(@"Error！：硬解码AAC get propery 失败, status= %d", (int)status);
        return nil;
    }
    for (unsigned int i = 0; i < count; i++) {
        if (type == description[i].mSubType && manufacture == description[i].mManufacturer) {
            desc = description[i];
            return &desc;
        }
    }
    return nil;
}

4.创建AuidoConverter
//获取解码器的描述信息  
AudioClassDescription *audioClassDesc = [self getAudioCalssDescriptionWithType:destFormatID fromManufacture:kAppleHardwareAudioCodecManufacturer];
    
// Create the AudioConverterRef.
AudioConverterRef converter = NULL;
if (![self checkError:AudioConverterNewSpecific(&inSourceFormat, &inDestinationFormat, inDestinationFormat.mChannelsPerFrame, audioClassDesc, &converter) withErrorString:@"Audio Converter New failed"]) {
     return NULL;
}else {
     printf("Audio converter create successful \n");
}

2.解码 AudioConverterFillComplexBuffer

/*!
    @function   AudioConverterFillComplexBuffer
    @abstract   Converts data supplied by an input callback function, supporting non-interleaved
                and packetized formats.

    @param      inAudioConverter
                    The AudioConverter to use.
    @param      inInputDataProc
                    A callback function which supplies the input data.
    @param      inInputDataProcUserData
                    A value for the use of the callback function.
    @param      ioOutputDataPacketSize
                    On entry, the capacity of outOutputData expressed in packets in the
                    converter's output format. On exit, the number of packets of converted
                    data that were written to outOutputData.
    @param      outOutputData
                    The converted output data is written to this buffer.
    @param      outPacketDescription
                    If non-null, and the converter's output uses packet descriptions, then
                    packet descriptions are written to this array. It must point to a memory
                    block capable of holding *ioOutputDataPacketSize packet descriptions.
                    (See AudioFormat.h for ways to determine whether an audio format
                    uses packet descriptions).
    @result     An OSStatus result code.

    @discussion
                Produces a buffer list of output data from an AudioConverter. The supplied input
                callback function is called whenever necessary.
*/
extern OSStatus
AudioConverterFillComplexBuffer(    AudioConverterRef                   inAudioConverter,
                                    AudioConverterComplexInputDataProc  inInputDataProc,
                                    void * __nullable                   inInputDataProcUserData,
                                    UInt32 *                            ioOutputDataPacketSize,
                                    AudioBufferList *                   outOutputData,
                                    AudioStreamPacketDescription * __nullable outPacketDescription)

例子

struct ConverterInfo {
    UInt32   sourceChannelsPerFrame;
    UInt32   sourceDataSize;
    void     *sourceBuffer;
    AudioStreamPacketDescription packetDesc;
};

typedef struct ConverterInfo ConverterInfoType;

OSStatus DecodeConverterComplexInputDataProc(AudioConverterRef              inAudioConverter,
                                             UInt32                         *ioNumberDataPackets,
                                             AudioBufferList                *ioData,
                                             AudioStreamPacketDescription   **outDataPacketDescription,
                                             void                           *inUserData) {
    ConverterInfoType *info = (ConverterInfoType *)inUserData;

    if (info->sourceDataSize <= 0) {
        ioNumberDataPackets = 0;
        return -1;
    }
    
    *outDataPacketDescription = &info->packetDesc;
    (*outDataPacketDescription)[0].mStartOffset             = 0;
    (*outDataPacketDescription)[0].mDataByteSize            = info->sourceDataSize;
    (*outDataPacketDescription)[0].mVariableFramesInPacket  = 0;
    
    ioData->mNumberBuffers              = 1;
    ioData->mBuffers[0].mData           = info->sourceBuffer;
    ioData->mBuffers[0].mNumberChannels = info->sourceChannelsPerFrame;
    ioData->mBuffers[0].mDataByteSize   = info->sourceDataSize;
    
    return noErr;
}

- (void)decodeFormatByConverter:(AudioConverterRef)audioConverter sourceBuffer:(void *)sourceBuffer sourceBufferSize:(UInt32)sourceBufferSize sourceFormat:(AudioStreamBasicDescription)sourceFormat dest:(AudioStreamBasicDescription)destFormat completeHandler:(void(^)(AudioBufferList *destBufferList, UInt32 outputPackets, AudioStreamPacketDescription *outputPacketDescriptions))completeHandler {

    // Note: audio convert must set 1024.
    UInt32 ioOutputDataPackets = kIOOutputDataPackets;
    UInt32 outputBufferSize = (UInt32)(ioOutputDataPackets * destFormat.mChannelsPerFrame * destFormat.mBytesPerFrame);
    // Set up output buffer list.
    AudioBufferList fillBufferList = {0};
    fillBufferList.mNumberBuffers = 1;
    fillBufferList.mBuffers[0].mNumberChannels  = destFormat.mChannelsPerFrame;
    fillBufferList.mBuffers[0].mDataByteSize    = outputBufferSize;
    fillBufferList.mBuffers[0].mData            = malloc(outputBufferSize * sizeof(char));
    
    ConverterInfoType userInfo        = {0};
    userInfo.sourceBuffer                = sourceBuffer;
    userInfo.sourceDataSize              = sourceBufferSize;
    userInfo.sourceChannelsPerFrame      = sourceFormat.mChannelsPerFrame;
    userInfo.packetDesc.mDataByteSize    = (UInt32)sourceBufferSize;
    userInfo.packetDesc.mStartOffset     = 0;
    userInfo.packetDesc.mVariableFramesInPacket = 0;
    
    AudioStreamPacketDescription outputPacketDesc = {0};
    OSStatus status = AudioConverterFillComplexBuffer(audioConverter,
                                                      DecodeConverterComplexInputDataProc,
                                                      &userInfo,
                                                      &ioOutputDataPackets,
                                                      &fillBufferList,
                                                      &outputPacketDesc);
    
    // if interrupted in the process of the conversion call, we must handle the error appropriately
    if (status != noErr) {
        if (status == kAudioConverterErr_HardwareInUse) {
            printf("Audio Converter returned kAudioConverterErr_HardwareInUse!\n");
        } else {
            if (![self checkError:status withErrorString:@"AudioConverterFillComplexBuffer error!"]) {
                return;
            }
        }
    } else {
        if (ioOutputDataPackets == 0) {
            // This is the EOF condition.
            status = noErr;
        }
        
        if (completeHandler) {
            completeHandler(&fillBufferList, ioOutputDataPackets, &outputPacketDesc);
        }
    }
}