关于 -- IPhone 的音频队列服务

音频队列服务提供一个可能，那就是：把音频数据块填充到音频队列服务缓冲区中，从而达到播放声音的目的，这种方式很类似 Windows 中的 waveOutWrite 方法。这样，我们就可以通过这个方法实现播放从网络上传输过来的音频数据。

我们需要通过队列服务提供的 AQOutputCallback 回调中填充缓冲区，在这里，我们就可以填充从网络传输过来的数据。

参看代码：

AudioStreamBasicDescription format; // 声音格式设置，这些设置要和采集时的配置一致

memset(&format, 0, sizeof(format));

format.mSampleRate = 44100; // 采样率 (立体声 = 8000)

format.mFormatID = kAudioFormatLinearPCM; // PCM 格式

format.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;

format.mChannelsPerFrame = 1; // 1:单声道；2:立体声

format.mBitsPerChannel = 16; // 语音每采样点占用位数

format.mBytesPerFrame = (format.mBitsPerChannel / * format.mChannelsPerFrame;

format.mFramesPerPacket = 1;

format.mBytesPerPacket = format.mBytesPerFrame * format.mFramesPerPacket;

AudioQueueRef queue;

AudioQueueNewOutput(&format,

AQPlayer::AQOutputCallback,

this, // opaque reference to whatever you like

CFRunLoopGetCurrent(),

kCFRunLoopCommonModes,

0,

&queue);

const int bufferSize = 0xA000; // 48K - around 1/2 sec of 44kHz 16 bit mono PCM

for (int i = 0; i < kNumberBuffers; ++i)

AudioQueueAllocateBufferWithPacketDescriptions(queue, bufferSize, 0, &mBuffers[i]);

AudioQueueSetParameter(queue, kAudioQueueParam_Volume, 1.0);

UInt32 category = kAudioSessionCategory_MediaPlayback;

AudioSessionSetProperty(kAudioSessionProperty_AudioCategory, sizeof(category), &category);

AudioSessionSetActive(true);

// prime the queue with some data before starting

for (int i = 0; i < kNumberBuffers; ++i)

OutputCallback(queue, mBuffers[i]);

AudioQueueStart(queue, NULL);

在CallBack中填出数据：

void OutputCallback(void* inUserData, AudioQueueRef inAQ, AudioQueueBufferRef inCompleteAQBuffer) {

// Fill

//AQPlayer* that = (AQPlayer*) inUserData;

inCompleteAQBuffer->mAudioDataByteSize = next->mAudioDataBytesCapacity;

for (int i = 0; i < inCompleteAQBuffer->mAudioDataByteSize; ++i)

next->mAudioData[i] = rand();

AudioQueueEnqueueBuffer(queue, inCompleteAQBuffer, 0, NULL);

}

音频采集参看：http://developer.apple.com/library/ios/#documentation/MusicAudio/Conceptual/

AudioQueueProgrammingGuide/AQRecord/RecordingAudio.html