IOS音频转换器 AudioConverterRef

1.创建

extern OSStatus
AudioConverterNewSpecific(  const AudioStreamBasicDescription * inSourceFormat,
const AudioStreamBasicDescription * inDestinationFormat,
UInt32                              inNumberClassDescriptions,
const AudioClassDescription *       inClassDescriptions,
AudioConverterRef __nullable * __nonnull outAudioConverter)

   inSourceFormat  和 inDestinationFormat 是传入的源音频格式和目标音频格式

   inNumberClassDescriptions 和 inClassDescriptions是传入的音频编码器描述类和它的个数

   outAudioConverter是传出的AudioConverter引用

      

AudioStreamBasicDescription inf = {0};
inf.mSampleRate = 44100;
inf.mChannelsPerFrame = 1;  //这里只能是1，否则报错
inf.mBitsPerChannel = 16;
inf.mFormatFlags =  kAudioFormatFlagIsSignedInteger | kAudioFormatFlagsNativeEndian | kAudioFormatFlagIsPacked;
inf.mFormatID = kAudioFormatLinearPCM;
inf.mFramesPerPacket = 1;
inf.mBytesPerFrame = inf.mBitsPerChannel * inf.mChannelsPerFrame / 8;
inf.mBytesPerPacket = inf.mFramesPerPacket*inf.mBytesPerFrame;

AudioStreamBasicDescription outf = { 0 };
outf.mFormatID = kAudioFormatMPEG4AAC;
outf.mFormatFlags = 0;
outf.mFramesPerPacket = 1024;
outf.mSampleRate = 44100;
outf.mChannelsPerFrame = 2;

<pre name="code" class="html">const OSType subtype = kAudioFormatMPEG4AAC;    // kAudioEncoderComponentType的时候使用目标类型
// kAudioDecoderComponentType的时候使用源类型

AudioClassDescription requestedCodecs[2] = {
{
kAudioEncoderComponentType,
subtype,
kAppleSoftwareAudioCodecManufacturer
},
{
kAudioEncoderComponentType,
subtype,
kAppleHardwareAudioCodecManufacturer
}
};
AudioConverterRef audioConverter;
OSStatus result = AudioConverterNewSpecific(inputFormat, outputFormat,2, requestedCodecs, &audioConverter);

2.释放

extern OSStatus
AudioConverterDispose(  AudioConverterRef   inAudioConverter)

inAudioConverter是AudioConverter的引用

if(audioConverter != NULL){
<span style="white-space:pre">	</span>AudioConverterDispose(audioConverter);
}

3.编码

extern OSStatus
AudioConverterFillComplexBuffer(    AudioConverterRef                   inAudioConverter,
AudioConverterComplexInputDataProc  inInputDataProc,
void * __nullable                   inInputDataProcUserData,
UInt32 *                            ioOutputDataPacketSize,
AudioBufferList *                   outOutputData,
AudioStreamPacketDescription * __nullable outPacketDescription)

inAudioConverter是传入的AudioConverter的引用

inInputDataProc是用户自己实现的获取编码数据的Callback函数（

inInputDataProcUserData是获取编码数据的Callback函数中使用的用户数据（一般传输编码session对象）

ioOutputDataPacketSize输出数据长度(通过获取AudioConverter的kAudioConverterPropertyMaximumOutputPacketSize属性获取或自定义足够的长度）

outOutputData输出数据

outPacketDescription输出数据描述

static OSStatus FillAudioDataCallback(AudioConverterRef inAudioConverter, UInt32 *ioNumberDataPackets,AudioBufferList *bufferList, AudioStreamPacketDescription **outDataPacketDescription, void *inUserData)

void *data = malloc(length);

UInt32 outputDataPackets = 1;

AudioBufferList outputData;
outputData.mNumberBuffers = 1;
outputData.mBuffers[0].mNumberChannels = 2;// 输出类型声道数
outputData.mBuffers[0].mDataByteSize = (UInt32)length;
outputData.mBuffers[0].mData = data;

AudioStreamPacketDescription outputPacketDescription;
OSStatus status = AudioConverterFillComplexBuffer(audioConverter, FillAudioDataCallback(__bridge void *)self, &outputDataPackets, &outputData, &outputPacketDescription);