iOS中获取音频流并提取pcm
最近工作中涉及采集手机麦克风的声音并且播放出来，我先后试了两种获取麦克风声音的方案：
1.此方案是通过AVCaptureSession获取的原始音频流，这个回调返回的音频数据
-(void)audioWithSampleBuffer:(CMSampleBufferRef)sampleBuffer {
}
格式为CMSampleBufferRef，现在要从中提取pcm数据才能播放，方法如下：
-(NSData *)convertAudioSamepleBufferToPcmData:(CMSampleBufferRef)sampleBuffer {
//获取pcm数据大小
size_t size = CMSampleBufferGetTotalSampleSize(sampleBuffer);
//分配空间
int8_t *audio_data = (int8_t *)malloc(size); memset(audio_data, 0, size);
//获取CMBlockBuffer, 这里面保存了PCM数据
CMBlockBufferRef blockBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
//将数据copy到我们分配的空间中
CMBlockBufferCopyDataBytes(blockBuffer, 0, size, audio_data);
NSData *data = [NSData dataWithBytes:audio_data length:size];
free(audio_data);
return data;
}
拿到这个data，就能直接播放了，此处参考了文章：https://blog.csdn.net/baidu_32469997/article/details/70017321
2.这个方案是通过AudioUnit获取的原始音频流，AudioUnit不详细介绍了，以下介绍从AudioUnit获取的原始数据中提取pcm：
首先AudioUnit有个录音的回调：
static OSStatus recordingCallback(void *inRefCon,
AudioUnitRenderActionFlags *ioActionFlags,
const AudioTimeStamp *inTimeStamp,
UInt32 inBusNumber,
UInt32 inNumberFrames,
AudioBufferList *ioData) {
// Because of the way our audio format (setup below) is chosen:
// we only need 1 buffer, since it is mono
// Samples are 16 bits = 2 bytes.
// 1 frame includes only 1 sample
AudioBuffer buffer;
buffer.mNumberChannels = 1;
buffer.mDataByteSize = inNumberFrames * 2;
buffer.mData = malloc( inNumberFrames * 2 );
// Put buffer in a AudioBufferList
AudioBufferList bufferList;
bufferList.mNumberBuffers = 1;
bufferList.mBuffers[0] = buffer;
// Then:
// Obtain recorded samples
OSStatus status;
status = AudioUnitRender([ystAudio audioUnit], ioActionFlags, inTimeStamp, inBusNumber, inNumberFrames, &bufferList);
checkStatus(status);
// Now, we have the samples we just read sitting in buffers in bufferList
// Process the new data
[ystAudio processAudio:&bufferList];
// release the malloc'ed data in the buffer we created earlier
free(bufferList.mBuffers[0].mData);
return noErr;
}
拿到这个bufferList，然后开始转换：
- (void) processAudio: (AudioBufferList*) bufferList{
AudioBuffer sourceBuffer = bufferList->mBuffers[0];
// fix tempBuffer size if it's the wrong size
if (tempBuffer.mDataByteSize != sourceBuffer.mDataByteSize) {
free(tempBuffer.mData);
tempBuffer.mDataByteSize = sourceBuffer.mDataByteSize;
tempBuffer.mData = malloc(sourceBuffer.mDataByteSize);
}
// copy incoming audio data to temporary buffer
memcpy(tempBuffer.mData, bufferList->mBuffers[0].mData, bufferList->mBuffers[0].mDataByteSize);
NSData *data = [NSData dataWithBytes:sourceBuffer.mData length:bufferList->mBuffers[0].mDataByteSize];
}
这里的data拿到的就是pcm数据了
