在iOS和Mac OS X中，音頻隊列Audio Queues是一個用來錄製和播放音頻的軟件對象，也就是說，能夠用來錄音和播放，錄音可以獲取實時的PCM原始音頻數據。bash
數據介紹cookie
（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); } } 複製代碼
Magic cookie 是一種不透明的數據格式，它和壓縮數據文件與流聯繫密切，若是文件數據爲CBR格式（無損），則不須要添加頭部信息，若是爲VBR須要添加,// 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中註冊的回調函數
// AudioQueue中註冊的回調函數
static void inputBufferHandler(void * inUserData,
AudioQueueRef inAQ,
AudioQueueBufferRef inBuffer,
const AudioTimeStamp * inStartTime,
UInt32 inNumPackets,
const AudioStreamPacketDescription* inPacketDesc) {
// 至關於本類對象實例
TVURecorder *recoder = (TVURecorder *)inUserData;
/*
inNumPackets 總包數：音頻隊列緩衝區大小 （在先前估算緩存區大小爲kXDXRecoderAACFramesPerPacket*2）/ （dataFormat.mFramesPerPacket (採集數據每一個包中有多少幀，此處在初始化設置中爲1) * dataFormat.mBytesPerFrame（每一幀中有多少個字節，此處在初始化設置中爲每一幀中兩個字節）），因此能夠根據該公式計算捕捉PCM數據時inNumPackets。
注意：若是採集的數據是PCM須要將dataFormat.mFramesPerPacket設置爲1，而本例中最終要的數據爲AAC,由於本例中使用的轉換器只有每次傳入1024幀才能開始工做,因此在AAC格式下須要將mFramesPerPacket設置爲1024.也就是採集到的inNumPackets爲1，在轉換器中傳入的inNumPackets應該爲AAC格式下默認的1，在此後寫入文件中也應該傳的是轉換好的inNumPackets,若是有特殊需求須要將採集的數據量小於1024,那麼須要將每次捕捉到的數據先預先存儲在一個buffer中,等到攢夠1024幀再進行轉換。
*/
// collect pcm data，能夠在此存儲
// 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 // 出隊 AudioQueueRef queue = recoder.mQueue; if (recoder.isRunning) { AudioQueueEnqueueBuffer(queue, inBuffer, 0, NULL); } } } 複製代碼
inNumPackets是inPacketDescs參數中包描述符（packet descriptions）的數量，若是你正在錄製一個VBR(可變比特率（variable bitrate））格式, 音頻隊列將會提供這個參數給你的回調函數，這個參數可讓你傳遞給AudioFileWritePackets函數. CBR (常量比特率（constant bitrate）) 格式不使用包描述符。對於CBR錄製，音頻隊列會設置這個參數而且將inPacketDescs這個參數設置爲NULL，官方解釋爲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);
// 初始化一個bufferList存儲數據
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設置爲1表示編碼產生1幀數據即返回，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. 在輸入表示輸出數據的最大容納能力 在轉換器的輸出格式上，在轉換完成時表示多少個包被寫入 */ UInt32 inNumPackets = 1; status = AudioConverterFillComplexBuffer(_encodeConvertRef, encodeConverterComplexInputDataProc, // 填充數據的回調函數 pcm_buffer, // 音頻隊列緩衝區中數據 &inNumPackets, bufferList, // 成功後將值賦給bufferList &outputPacketDescriptions); // 輸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. 將轉換器轉換出來的包寫入文件中，inNumPackets表示寫入文件的起始位置 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,用於記錄寫入文件的位置 } return bufferList; } 複製代碼
1). AudioUnit是 iOS提供的爲了支持混音，均衡，格式轉換，實時輸入輸出用於錄製，回放，離線渲染和實時回話(VOIP)，這讓咱們能夠動態加載和使用，即從iOS應用程序中接收這些強大而靈活的插件。它是iOS音頻中最低層，因此除非你須要合成聲音的實時播放，低延遲的I/O，或特定聲音的特定特色。 Audio unit scopes and elements ：
上圖是一個AudioUnit的組成結構，A scope 主要使用到的輸入kAudioUnitScope_Input和輸出kAudioUnitScope_Output。Element 是嵌套在audio unit scope的編程上下文。
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默認的buffer而使用咱們本身寫的全局BUFFER,用來接收每次採集的PCM數據，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);
}
複製代碼
解析
本例經過禁用AudioUnit默認的buffer而使用咱們本身寫的全局BUFFER,用來接收每次採集的PCM數據，Disable AU buffer allocation for the recorder, we allocate our own.還有一種寫法是可使用回調中提供的ioData存儲採集的數據，這裏使用全局的buff是爲了供其餘地方使用，可根據須要自行決定採用哪一種方式，若不採用全局buffer則不可採用上述禁用操做。
// 由於本例只作錄音功能，未實現播放功能，因此沒有設置播放相關設置。
- (void)setAudioUnitPropertyAndFormat {
OSStatus status;
[self setUpRecoderWithFormatID:kAudioFormatLinearPCM];
// 應用audioUnit設置的格式
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);
}
// 去除回聲開關
UInt32 echoCancellation;
AudioUnitSetProperty(_audioUnit,
kAUVoiceIOProperty_BypassVoiceProcessing,
kAudioUnitScope_Global,
0,
&echoCancellation,
sizeof(echoCancellation));
// AudioUnit輸入端默認是關閉，須要將他打開
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. 此處的設置爲官方推薦設置,可根據具體需求修改部分設置
//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採集pcm須要這麼設置
}
}
複製代碼
-(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); } } 複製代碼
解析
Magic cookie 是一種不透明的數據格式，它和壓縮數據文件與流聯繫密切，若是文件數據爲CBR格式（無損），則不須要添加頭部信息，若是爲VBR須要添加,// 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.
