「这是我参与2022首次更文挑战的第7天，活动详情查看：2022首次更文挑战」。 这篇文章讲解使用AudioToolBox硬解码音频，关于使用AudioToolBox硬编码音频，使用VideoToolBox编解码视频，可以看我之前的文章。
AudioToolBox
- 和VideoToolBox一样，一个纯C偏底层的框架
- 输入AAC数据，解码出PCM
用到的几个核心函数
AudioConverterNewSpecific，初始化音频转化器- 参数1：输入音频格式描述
- 参数2：输出音频格式描述
- 参数3：class desc的数量
- 参数4：class desc
- 参数5：创建的解码器
AudioFormatGetPropertyInfo,获取解码器的信息- 参数1：编码器类型（解码）
- 参数2：类型描述大小
- 参数3：类型描述
- 参数4：大小
AudioFormatGetProperty，获取编码器属性格式AudioConverterFillComplexBuffer,配置解码的数据，开始解码
一 初始化音频转化器
- 这里也可以像编码一样接收到数据在创建
- 输入参数我直接从默认配置里拿了，假设编码解码的配置是一样，应用到实际项目应适当修改
- mSampleRate 采样率
- mChannelsPerFrame 输出声道数
- mFormatID 输出格式
- mFormatFlags 编码格式
- mFramesPerPacket 每一个packet帧数
- mBitsPerChannel 数据中每个通道的采样位数
- mBytesPerFrame 每一帧大小
- mBytesPerPacket 每个packet大小帧大小 * 帧数）
- mReserved 对其方式 0(标识8字节对其)
#pragma mark - 创建解码器
- (void)setupDecoder {
// 输出参数pcm
AudioStreamBasicDescription outputAudioDes = {0};
outputAudioDes.mSampleRate = (Float64)_config.sampleRate; // 采样率*
outputAudioDes.mChannelsPerFrame = (UInt32)_config.channelCount; // 输出声道数*
outputAudioDes.mFormatID = kAudioFormatLinearPCM; // 输出格式*
outputAudioDes.mFormatFlags = (kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked); // 编码 12*
outputAudioDes.mFramesPerPacket = 1; // 每一个packet帧数 ；*
outputAudioDes.mBitsPerChannel = 16; // 数据帧中每个通道的采样位数。*
// 每一帧大小（采样位数 / 8 *声道数）*
outputAudioDes.mBytesPerFrame = outputAudioDes.mBitsPerChannel / 8 *outputAudioDes.mChannelsPerFrame;
// 每个packet大小（帧大小 * 帧数）*
outputAudioDes.mBytesPerPacket = outputAudioDes.mBytesPerFrame * outputAudioDes.mFramesPerPacket;
outputAudioDes.mReserved = 0; //对其方式 0(8字节对齐)*
// 输入参数aac，原文件格式*
AudioStreamBasicDescription inputAduioDes = {0};
inputAduioDes.mSampleRate = (Float64)_config.sampleRate;
inputAduioDes.mFormatID = kAudioFormatMPEG4AAC;
inputAduioDes.mFormatFlags = kMPEG4Object_AAC_LC;
inputAduioDes.mFramesPerPacket = 1024;
inputAduioDes.mChannelsPerFrame = (UInt32)_config.channelCount;
// 填充输出相关信息*
UInt32 inDesSize = sizeof(inputAduioDes);
AudioFormatGetProperty(kAudioFormatProperty_FormatInfo, 0, NULL, &inDesSize, &inputAduioDes);
// 获取解码器的描述信息(只能传入software)*
AudioClassDescription *audioClassDesc = [self getAudioCalssDescriptionWithType:outputAudioDes.mFormatID fromManufacture:kAppleSoftwareAudioCodecManufacturer];
/** *创建converter*
*参数1：输入音频格式描述*
*参数2：输出音频格式描述*
*参数3：class desc的数量*
*参数4：class desc*
*参数5：创建的解码器*
*/
OSStatus status = AudioConverterNewSpecific(&inputAduioDes, &outputAudioDes, 1, audioClassDesc, &_audioConverter);
if (status != noErr) {
NSLog(@"CQAudioDecoder - Error！：硬解码AAC创建失败, status= %d", (int)status);
return;
}
}
- 获取解码器的描述信息，创建解码器时需要用到
/**
*获取解码器类型描述*
*参数1：类型*
*/
- (AudioClassDescription *)getAudioCalssDescriptionWithType:(AudioFormatID)type fromManufacture: (uint32_t)manufacture {
static AudioClassDescription desc;
UInt32 decoderSpecific = type;
*// 获取满足AAC解码器的总大小*
UInt32 size;
/**
*参数1：编码器类型（解码）*
*参数2：类型描述大小*
*参数3：类型描述*
*参数4：大小*
*/
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_Encoders, 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;
}
二 接收数据，调用音频转换器解码
- 实时接收数据，异步解码
- (void)audioDecodeWithAACData:(**NSData** *)aacData {
if (!_audioConverter) { return; }
dispatch_async(_decodeQueue, ^{
// 记录aac 作为参数参入 给到 解码回调函数*
CQAudioUserData userData = {0};
userData.channelCount = (UInt32)self.config.channelCount;
userData.data = (char *)[aacData bytes];
userData.size = (UInt32)aacData.length;
userData.packetDesc.mDataByteSize = (UInt32)aacData.length;
userData.packetDesc.mStartOffset = 0;
userData.packetDesc.mVariableFramesInPacket = 0;
// 输出大小和packet个数
UInt32 pcmBufferSize = (UInt32)(2048 * self.config.channelCount);
UInt32 pcmDataPacketSize = 1024;
// 创建临时容器pcm
uint8_t *pcmBuffer = malloc(pcmBufferSize);
memset(pcmBuffer, 0, pcmBufferSize);
// 输出buffer
AudioBufferList outAudioBufferList = {0};
outAudioBufferList.mNumberBuffers = 1;
outAudioBufferList.mBuffers[0].mNumberChannels = (uint32_t)self.config.channelCount;
outAudioBufferList.mBuffers[0].mDataByteSize = (UInt32)pcmBufferSize;
outAudioBufferList.mBuffers[0].mData = pcmBuffer;
// 输出描述
AudioStreamPacketDescription outputPacketDesc = {0};
// 配置填充函数，获取输出数据
OSStatus status = AudioConverterFillComplexBuffer(self.audioConverter, &AudioDecoderConverterComplexInputDataProc, &userData, &pcmDataPacketSize, &outAudioBufferList, &outputPacketDesc);
if (status != noErr) {
NSLog(@"Error: AAC Decoder error, status=%d",(int)status);
return;
}
// 如果获取到数据
if (outAudioBufferList.mBuffers[0].mDataByteSize > 0) {
NSData *rawData = [NSData dataWithBytes:outAudioBufferList.mBuffers[0].mData length:outAudioBufferList.mBuffers[0].mDataByteSize];
dispatch_async(self.callbackQueue, ^{
if (self.delegate && [self.delegate respondsToSelector:@selector(audioDecoder:didDecodeSuccessWithPCMData:)]) {
[self.delegate audioDecoder:self didDecodeSuccessWithPCMData:rawData];
}
});
}
free(pcmBuffer);
});
}
三 在回调里不断填充数据
#pragma mark - AudioToolBox
// 解码器回调函数，在这里填充回调数据
static OSStatus AudioDecoderConverterComplexInputDataProc( AudioConverterRef inAudioConverter, UInt32 *ioNumberDataPackets, AudioBufferList *ioData, AudioStreamPacketDescription **outDataPacketDescription, void *inUserData) {
CQAudioUserData *audioDecoder = (CQAudioUserData *)(inUserData);
if (audioDecoder->size <= 0) {
ioNumberDataPackets = 0;
return -1;
}
// 填充数据
*outDataPacketDescription = &audioDecoder->packetDesc;
(*outDataPacketDescription)[0].mStartOffset = 0;
(*outDataPacketDescription)[0].mDataByteSize = audioDecoder->size;
(*outDataPacketDescription)[0].mVariableFramesInPacket = 0;
ioData->mBuffers[0].mData = audioDecoder->data;
ioData->mBuffers[0].mDataByteSize = audioDecoder->size;
ioData->mBuffers[0].mNumberChannels = audioDecoder->channelCount;
return noErr;
}
