在iOS和Mac OS X中，音频队列Audio Queues是一个用来录制和播放音频的软件对象，也就是说，可以用来录音和播放，录音能够获取实时的PCM原始音频数据。
数据介绍
（1）In CBR (constant bit rate) formats, such as linear PCM and IMA/ADPCM, all packets are the same size.
（2）In VBR (variable bit rate) formats, such as AAC, Apple Lossless, and MP3, all packets have the same number of frames but the number of bits in each sample value can vary.
（3）In VFR (variable frame rate) formats, packets have a varying number of frames. There are no commonly used formats of this type.
-(void)copyEncoderCookieToFile
{
// Grab the cookie from the converter and write it to the destination file.
UInt32 cookieSize = 0;
OSStatus error = AudioConverterGetPropertyInfo(_encodeConvertRef, kAudioConverterCompressionMagicCookie, &cookieSize, NULL);
// If there is an error here, then the format doesn't have a cookie - this is perfectly fine as som formats do not.
// log4cplus_info("cookie","cookie status:%d %d",(int)error, cookieSize);
if (error == noErr && cookieSize != 0) {
char *cookie = (char *)malloc(cookieSize * sizeof(char));
// UInt32 *cookie = (UInt32 *)malloc(cookieSize * sizeof(UInt32));
error = AudioConverterGetProperty(_encodeConvertRef, kAudioConverterCompressionMagicCookie, &cookieSize, cookie);
// log4cplus_info("cookie","cookie size status:%d",(int)error);
if (error == noErr) {
error = AudioFileSetProperty(mRecordFile, kAudioFilePropertyMagicCookieData, cookieSize, cookie);
// log4cplus_info("cookie","set cookie status:%d ",(int)error);
if (error == noErr) {
UInt32 willEatTheCookie = false;
error = AudioFileGetPropertyInfo(mRecordFile, kAudioFilePropertyMagicCookieData, NULL, &willEatTheCookie);
printf("Writing magic cookie to destination file: %u\n cookie:%d \n", (unsigned int)cookieSize, willEatTheCookie);
} else {
printf("Even though some formats have cookies, some files don't take them and that's OK\n");
}
} else {
printf("Could not Get kAudioConverterCompressionMagicCookie from Audio Converter!\n");
}
free(cookie);
}
}
Magic cookie 是一种不透明的数据格式，它和压缩数据文件与流联系密切，如果文件数据为CBR格式（无损），则不需要添加头部信息，如果为VBR需要添加,// if collect CBR needn't set magic cookie , if collect VBR should set magic cookie, if needn't to convert format that can be setting by audio queue directly.
(5).AudioQueue中注册的回调函数
// AudioQueue中注册的回调函数
static void inputBufferHandler(void * inUserData,
AudioQueueRef inAQ,
AudioQueueBufferRef inBuffer,
const AudioTimeStamp * inStartTime,
UInt32 inNumPackets,
const AudioStreamPacketDescription* inPacketDesc) {
// 相当于本类对象实例
TVURecorder *recoder = (TVURecorder *)inUserData;
/*
inNumPackets 总包数：音频队列缓冲区大小 （在先前估算缓存区大小为kXDXRecoderAACFramesPerPacket*2）/ （dataFormat.mFramesPerPacket (采集数据每个包中有多少帧，此处在初始化设置中为1) * dataFormat.mBytesPerFrame（每一帧中有多少个字节，此处在初始化设置中为每一帧中两个字节）），所以可以根据该公式计算捕捉PCM数据时inNumPackets。
注意：如果采集的数据是PCM需要将dataFormat.mFramesPerPacket设置为1，而本例中最终要的数据为AAC,因为本例中使用的转换器只有每次传入1024帧才能开始工作,所以在AAC格式下需要将mFramesPerPacket设置为1024.也就是采集到的inNumPackets为1，在转换器中传入的inNumPackets应该为AAC格式下默认的1，在此后写入文件中也应该传的是转换好的inNumPackets,如果有特殊需求需要将采集的数据量小于1024,那么需要将每次捕捉到的数据先预先存储在一个buffer中,等到攒够1024帧再进行转换。
*/
// collect pcm data，可以在此存储
// First case : collect data not is 1024 frame, if collect data not is 1024 frame, we need to save data to pcm_buffer untill 1024 frame
memcpy(pcm_buffer+pcm_buffer_size, inBuffer->mAudioData, inBuffer->mAudioDataByteSize);
pcm_buffer_size = pcm_buffer_size + inBuffer->mAudioDataByteSize;
if(inBuffer->mAudioDataByteSize != kXDXRecoderAACFramesPerPacket*2)
NSLog(@"write pcm buffer size:%d, totoal buff size:%d", inBuffer->mAudioDataByteSize, pcm_buffer_size);
frameCount++;
// Second case : If the size of the data collection is not required, we can let mic collect 1024 frame so that don't need to write firtst case, but it is recommended to write the above code because of agility
// if collect data is added to 1024 frame
if(frameCount == totalFrames) {
AudioBufferList *bufferList = convertPCMToAAC(recoder);
pcm_buffer_size = 0;
frameCount = 0;
// free memory
free(bufferList->mBuffers[0].mData);
free(bufferList);
// begin write audio data for record audio only
// 出队
AudioQueueRef queue = recoder.mQueue;
if (recoder.isRunning) {
AudioQueueEnqueueBuffer(queue, inBuffer, 0, NULL);
}
}
}
inNumPackets是inPacketDescs参数中包描述符（packet descriptions）的数量，如果你正在录制一个VBR(可变比特率（variable bitrate））格式, 音频队列将会提供这个参数给你的回调函数，这个参数可以让你传递给AudioFileWritePackets函数. CBR (常量比特率（constant bitrate）) 格式不使用包描述符。对于CBR录制，音频队列会设置这个参数并且将inPacketDescs这个参数设置为NULL，官方解释为The number of packets of audio data sent to the callback in the inBuffer parameter.
// PCM -> AAC
AudioBufferList* convertPCMToAAC (AudioQueueBufferRef inBuffer, XDXRecorder *recoder) {
UInt32 maxPacketSize = 0;
UInt32 size = sizeof(maxPacketSize);
OSStatus status;
status = AudioConverterGetProperty(_encodeConvertRef,
kAudioConverterPropertyMaximumOutputPacketSize,
&size,
&maxPacketSize);
// log4cplus_info("AudioConverter","kAudioConverterPropertyMaximumOutputPacketSize status:%d \n",(int)status);
// 初始化一个bufferList存储数据
AudioBufferList *bufferList = (AudioBufferList *)malloc(sizeof(AudioBufferList));
bufferList->mNumberBuffers = 1;
bufferList->mBuffers[0].mNumberChannels = _targetDes.mChannelsPerFrame;
bufferList->mBuffers[0].mData = malloc(maxPacketSize);
bufferList->mBuffers[0].mDataByteSize = pcm_buffer_size;
AudioStreamPacketDescription outputPacketDescriptions;
/*
inNumPackets设置为1表示编码产生1帧数据即返回，官方：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. 在输入表示输出数据的最大容纳能力 在转换器的输出格式上，在转换完成时表示多少个包被写入
*/
UInt32 inNumPackets = 1;
status = AudioConverterFillComplexBuffer(_encodeConvertRef,
encodeConverterComplexInputDataProc, // 填充数据的回调函数
pcm_buffer, // 音频队列缓冲区中数据
&inNumPackets,
bufferList, // 成功后将值赋给bufferList
&outputPacketDescriptions); // 输出包包含的一些信息
log4cplus_info("AudioConverter","set AudioConverterFillComplexBuffer status:%d",(int)status);
if (recoder.needsVoiceDemo) {
// if inNumPackets set not correct, file will not normally play. 将转换器转换出来的包写入文件中，inNumPackets表示写入文件的起始位置
OSStatus status = AudioFileWritePackets(recoder.mRecordFile,
FALSE,
bufferList->mBuffers[0].mDataByteSize,
&outputPacketDescriptions,
recoder.mRecordPacket,
&inNumPackets,
bufferList->mBuffers[0].mData);
// log4cplus_info("write file","write file status = %d",(int)status);
recoder.mRecordPacket += inNumPackets; // Used to record the location of the write file,用于记录写入文件的位置
}
return bufferList;
}
1). AudioUnit是 iOS提供的为了支持混音，均衡，格式转换，实时输入输出用于录制，回放，离线渲染和实时回话(VOIP)，这让我们可以动态加载和使用，即从iOS应用程序中接收这些强大而灵活的插件。它是iOS音频中最低层，所以除非你需要合成声音的实时播放，低延迟的I/O，或特定声音的特定特点。
Audio unit scopes and elements ：
上图是一个AudioUnit的组成结构，A scope 主要使用到的输入kAudioUnitScope_Input和输出kAudioUnitScope_Output。Element 是嵌套在audio unit scope的编程上下文。
To find an audio unit at runtime, start by specifying its type, subtype, and manufacturer keys in an audio component description data structure. You do this whether using the audio unit or audio processing graph API.
- (void)initBuffer {
// 禁用AudioUnit默认的buffer而使用我们自己写的全局BUFFER,用来接收每次采集的PCM数据，Disable AU buffer allocation for the recorder, we allocate our own.
UInt32 flag = 0;
OSStatus status = AudioUnitSetProperty(_audioUnit,
kAudioUnitProperty_ShouldAllocateBuffer,
kAudioUnitScope_Output,
INPUT_BUS,
&flag,
sizeof(flag));
if (status != noErr) {
// log4cplus_info("Audio Recoder", "couldn't AllocateBuffer of AudioUnitCallBack, status : %d \n",status);
}
_buffList = (AudioBufferList*)malloc(sizeof(AudioBufferList));
_buffList->mNumberBuffers = 1;
_buffList->mBuffers[0].mNumberChannels = dataFormat.mChannelsPerFrame;
_buffList->mBuffers[0].mDataByteSize = kTVURecoderPCMMaxBuffSize * sizeof(short);
_buffList->mBuffers[0].mData = (short *)malloc(sizeof(short) * kTVURecoderPCMMaxBuffSize);
}
解析
本例通过禁用AudioUnit默认的buffer而使用我们自己写的全局BUFFER,用来接收每次采集的PCM数据，Disable AU buffer allocation for the recorder, we allocate our own.还有一种写法是可以使用回调中提供的ioData存储采集的数据，这里使用全局的buff是为了供其他地方使用，可根据需要自行决定采用哪种方式，若不采用全局buffer则不可采用上述禁用操作。
// 因为本例只做录音功能，未实现播放功能，所以没有设置播放相关设置。
- (void)setAudioUnitPropertyAndFormat {
OSStatus status;
[self setUpRecoderWithFormatID:kAudioFormatLinearPCM];
// 应用audioUnit设置的格式
status = AudioUnitSetProperty(_audioUnit,
kAudioUnitProperty_StreamFormat,
kAudioUnitScope_Output,
INPUT_BUS,
&dataFormat,
sizeof(dataFormat));
if (status != noErr) {
// log4cplus_info("Audio Recoder", "couldn't set the input client format on AURemoteIO, status : %d \n",status);
}
// 去除回声开关
UInt32 echoCancellation;
AudioUnitSetProperty(_audioUnit,
kAUVoiceIOProperty_BypassVoiceProcessing,
kAudioUnitScope_Global,
0,
&echoCancellation,
sizeof(echoCancellation));
// AudioUnit输入端默认是关闭，需要将他打开
UInt32 flag = 1;
status = AudioUnitSetProperty(_audioUnit,
kAudioOutputUnitProperty_EnableIO,
kAudioUnitScope_Input,
INPUT_BUS,
&flag,
sizeof(flag));
if (status != noErr) {
// log4cplus_info("Audio Recoder", "could not enable input on AURemoteIO, status : %d \n",status);
}
}
-(void)setUpRecoderWithFormatID:(UInt32)formatID {
// Notice : The settings here are official recommended settings,can be changed according to specific requirements. 此处的设置为官方推荐设置,可根据具体需求修改部分设置
//setup auido sample rate, channel number, and format ID
memset(&dataFormat, 0, sizeof(dataFormat));
UInt32 size = sizeof(dataFormat.mSampleRate);
AudioSessionGetProperty(kAudioSessionProperty_CurrentHardwareSampleRate,
&size,
&dataFormat.mSampleRate);
dataFormat.mSampleRate = kXDXAudioSampleRate;
size = sizeof(dataFormat.mChannelsPerFrame);
AudioSessionGetProperty(kAudioSessionProperty_CurrentHardwareInputNumberChannels,
&size,
&dataFormat.mChannelsPerFrame);
dataFormat.mFormatID = formatID;
dataFormat.mChannelsPerFrame = 1;
if (formatID == kAudioFormatLinearPCM) {
if (self.releaseMethod == XDXRecorderReleaseMethodAudioQueue) {
dataFormat.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;
}elseif (self.releaseMethod == XDXRecorderReleaseMethodAudioQueue) {
dataFormat.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
}
dataFormat.mBitsPerChannel = 16;
dataFormat.mBytesPerPacket = dataFormat.mBytesPerFrame = (dataFormat.mBitsPerChannel / 8) * dataFormat.mChannelsPerFrame;
dataFormat.mFramesPerPacket = kXDXRecoderPCMFramesPerPacket; // 用AudioQueue采集pcm需要这么设置
}
}
-(void)copyEncoderCookieToFile
{
// Grab the cookie from the converter and write it to the destination file.
UInt32 cookieSize = 0;
OSStatus error = AudioConverterGetPropertyInfo(_encodeConvertRef, kAudioConverterCompressionMagicCookie, &cookieSize, NULL);
// If there is an error here, then the format doesn't have a cookie - this is perfectly fine as som formats do not.
// log4cplus_info("cookie","cookie status:%d %d",(int)error, cookieSize);
if (error == noErr && cookieSize != 0) {
char *cookie = (char *)malloc(cookieSize * sizeof(char));
// UInt32 *cookie = (UInt32 *)malloc(cookieSize * sizeof(UInt32));
error = AudioConverterGetProperty(_encodeConvertRef, kAudioConverterCompressionMagicCookie, &cookieSize, cookie);
// log4cplus_info("cookie","cookie size status:%d",(int)error);
if (error == noErr) {
error = AudioFileSetProperty(mRecordFile, kAudioFilePropertyMagicCookieData, cookieSize, cookie);
// log4cplus_info("cookie","set cookie status:%d ",(int)error);
if (error == noErr) {
UInt32 willEatTheCookie = false;
error = AudioFileGetPropertyInfo(mRecordFile, kAudioFilePropertyMagicCookieData, NULL, &willEatTheCookie);
printf("Writing magic cookie to destination file: %u\n cookie:%d \n", (unsigned int)cookieSize, willEatTheCookie);
} else {
printf("Even though some formats have cookies, some files don't take them and that's OK\n");
}
} else {
printf("Could not Get kAudioConverterCompressionMagicCookie from Audio Converter!\n");
}
free(cookie);
}
}
解析
Magic cookie 是一种不透明的数据格式，它和压缩数据文件与流联系密切，如果文件数据为CBR格式（无损），则不需要添加头部信息，如果为VBR需要添加,// if collect CBR needn't set magic cookie , if collect VBR should set magic cookie, if needn't to convert format that can be setting by audio queue directly.
