【发布时间】：2012-07-09 02:01:33
【问题描述】：
目前，我正在做一个小测试项目，看看是否可以从 AVAssetReader 获取样本，以便在 iOS 上使用 AudioQueue 进行播放。
我读过这个： (Play raw uncompressed sound with AudioQueue, no sound) 还有这个：（How to correctly read decoded PCM samples on iOS using AVAssetReader -- currently incorrect decoding），
这两者实际上都有帮助。在阅读之前，我完全没有声音。现在，我得到了声音，但音频播放速度非常快。这是我第一次涉足音频编程，非常感谢任何帮助。
我这样初始化阅读器：
NSDictionary * outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:kAudioFormatLinearPCM], AVFormatIDKey,
[NSNumber numberWithFloat:44100.0], AVSampleRateKey,
[NSNumber numberWithInt:2], AVNumberOfChannelsKey,
[NSNumber numberWithInt:16], AVLinearPCMBitDepthKey,
[NSNumber numberWithBool:NO], AVLinearPCMIsNonInterleaved,
[NSNumber numberWithBool:NO], AVLinearPCMIsFloatKey,
[NSNumber numberWithBool:NO], AVLinearPCMIsBigEndianKey,
nil];
output = [[AVAssetReaderAudioMixOutput alloc] initWithAudioTracks:uasset.tracks audioSettings:outputSettings];
[reader addOutput:output];
...
我就这样抓取了数据：
CMSampleBufferRef ref= [output copyNextSampleBuffer];
// NSLog(@"%@",ref);
if(ref==NULL)
return;
//copy data to file
//read next one
AudioBufferList audioBufferList;
NSMutableData *data = [NSMutableData data];
CMBlockBufferRef blockBuffer;
CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(ref, NULL, &audioBufferList, sizeof(audioBufferList), NULL, NULL, 0, &blockBuffer);
// NSLog(@"%@",blockBuffer);
if(blockBuffer==NULL)
{
[data release];
return;
}
if(&audioBufferList==NULL)
{
[data release];
return;
}
//stash data in same object
for( int y=0; y<audioBufferList.mNumberBuffers; y++ )
{
// NSData* throwData;
AudioBuffer audioBuffer = audioBufferList.mBuffers[y];
[self.delegate streamer:self didGetAudioBuffer:audioBuffer];
/*
Float32 *frame = (Float32*)audioBuffer.mData;
throwData = [NSData dataWithBytes:audioBuffer.mData length:audioBuffer.mDataByteSize];
[self.delegate streamer:self didGetAudioBuffer:throwData];
[data appendBytes:audioBuffer.mData length:audioBuffer.mDataByteSize];
*/
}
最终将我们带到音频队列，以这种方式设置：
//Apple's own code for canonical PCM
audioDesc.mSampleRate = 44100.0;
audioDesc.mFormatID = kAudioFormatLinearPCM;
audioDesc.mFormatFlags = kAudioFormatFlagsAudioUnitCanonical;
audioDesc.mBytesPerPacket = 2 * sizeof (AudioUnitSampleType); // 8
audioDesc.mFramesPerPacket = 1;
audioDesc.mBytesPerFrame = 1 * sizeof (AudioUnitSampleType); // 8
audioDesc.mChannelsPerFrame = 2;
audioDesc.mBitsPerChannel = 8 * sizeof (AudioUnitSampleType); // 32
err = AudioQueueNewOutput(&audioDesc, handler_OSStreamingAudio_queueOutput, self, NULL, NULL, 0, &audioQueue);
if(err){
#pragma warning handle error
//never errs, am using breakpoint to check
return;
}
我们就这样排队
while (inNumberBytes)
{
size_t bufSpaceRemaining = kAQDefaultBufSize - bytesFilled;
if (bufSpaceRemaining < inNumberBytes)
{
AudioQueueBufferRef fillBuf = audioQueueBuffer[fillBufferIndex];
fillBuf->mAudioDataByteSize = bytesFilled;
err = AudioQueueEnqueueBuffer(audioQueue, fillBuf, 0, NULL);
}
bufSpaceRemaining = kAQDefaultBufSize - bytesFilled;
size_t copySize;
if (bufSpaceRemaining < inNumberBytes)
{
copySize = bufSpaceRemaining;
}
else
{
copySize = inNumberBytes;
}
if (bytesFilled > packetBufferSize)
{
return;
}
AudioQueueBufferRef fillBuf = audioQueueBuffer[fillBufferIndex];
memcpy((char*)fillBuf->mAudioData + bytesFilled, (const char*)(inInputData + offset), copySize);
bytesFilled += copySize;
packetsFilled = 0;
inNumberBytes -= copySize;
offset += copySize;
}
}
我试图尽可能地包含代码，以便让每个人都能轻松指出我在哪里是个白痴。话虽如此，我感觉我的问题出现在轨道阅读器的输出设置声明中或 AudioQueue 的实际声明中（我向队列描述我将发送什么样的音频）。事实是，我真的不知道如何在数学上实际生成这些数字（每个数据包的字节数，每个数据包的帧数，你有什么）。对此的解释将不胜感激，并提前感谢您的帮助。
【问题讨论】：
标签： objective-c ios core-audio audioqueueservices avassetreader