ExtAudioFileWrite到m4a / aac在双核设备上失败（ipad 2，iphone 4s） [英] ExtAudioFileWrite to m4a/aac failing on dual-core devices (ipad 2, iphone 4s)

问题描述

我写了一个循环来使用扩展音频文件服务将我的应用程序生成的pcm音频数据编码到aac。编码同步发生在后台线程中，而不是实时发生。

I wrote a loop to encode pcm audio data generated by my app to aac using Extended Audio File Services. The encoding takes place in a background thread synchronously, and not in real-time.

对于ios 4和5，编码在ipad 1和iphone 3gs / 4上完美运行但是，对于双核设备（iphone 4s，ipad 2），第三次调用ExtAudioFileWrite会使编码线程崩溃而没有堆栈跟踪且没有错误代码。

The encoding works flawlessly on ipad 1 and iphone 3gs/4 for both ios 4 and 5. However, for dual-core devices (iphone 4s, ipad 2) the third call to ExtAudioFileWrite crashes the encoding thread with no stack trace and no error code.

这是有问题的代码：

数据格式

AudioStreamBasicDescription AUCanonicalASBD(Float64 sampleRate, 
                                        UInt32 channel){
AudioStreamBasicDescription audioFormat;
audioFormat.mSampleRate         = sampleRate;
audioFormat.mFormatID           = kAudioFormatLinearPCM;
audioFormat.mFormatFlags        = kAudioFormatFlagsAudioUnitCanonical;
audioFormat.mChannelsPerFrame   = channel;
audioFormat.mBytesPerPacket     = sizeof(AudioUnitSampleType);
audioFormat.mBytesPerFrame      = sizeof(AudioUnitSampleType);
audioFormat.mFramesPerPacket    = 1;
audioFormat.mBitsPerChannel     = 8 * sizeof(AudioUnitSampleType);
audioFormat.mReserved           = 0;
return audioFormat;
}

AudioStreamBasicDescription MixdownAAC(void){
AudioStreamBasicDescription audioFormat;
audioFormat.mSampleRate         = 44100.0;
audioFormat.mFormatID           = kAudioFormatMPEG4AAC;
audioFormat.mFormatFlags        = kMPEG4Object_AAC_Main;
audioFormat.mChannelsPerFrame   = 2;
audioFormat.mBytesPerPacket     = 0;
audioFormat.mBytesPerFrame      = 0;
audioFormat.mFramesPerPacket    = 1024;
audioFormat.mBitsPerChannel     = 0;
audioFormat.mReserved           = 0;
return audioFormat;
}

渲染循环

OSStatus err;
ExtAudioFileRef outFile;
NSURL *mixdownURL = [NSURL fileURLWithPath:filePath isDirectory:NO];

// internal data format
AudioStreamBasicDescription localFormat = AUCanonicalASBD(44100.0, 2);

// output file format
AudioStreamBasicDescription mixdownFormat = MixdownAAC();
err = ExtAudioFileCreateWithURL((CFURLRef)mixdownURL,
                             kAudioFileM4AType,
                             &mixdownFormat, 
                             NULL,
                             kAudioFileFlags_EraseFile,
                             &outFile);


err = ExtAudioFileSetProperty(outFile, kExtAudioFileProperty_ClientDataFormat, sizeof(AudioStreamBasicDescription), &localFormat);

// prep
AllRenderData *allData = &allRenderData;
writeBuffer = malloc(sizeof(AudioBufferList) + (2*sizeof(AudioBuffer)));
writeBuffer->mNumberBuffers = 2;
writeBuffer->mBuffers[0].mNumberChannels = 1;
writeBuffer->mBuffers[0].mDataByteSize = bufferBytes;
writeBuffer->mBuffers[0].mData = malloc(bufferBytes);
writeBuffer->mBuffers[1].mNumberChannels = 1;
writeBuffer->mBuffers[1].mDataByteSize = bufferBytes;
writeBuffer->mBuffers[1].mData = malloc(bufferBytes);

memset(writeBuffer->mBuffers[0].mData, 0, bufferBytes);
memset(writeBuffer->mBuffers[1].mData, 0, bufferBytes);

UInt32 framesToGet;
UInt32 frameCount = allData->gLoopStartFrame;
UInt32 startFrame = allData->gLoopStartFrame;
UInt32 lastFrame = allData->gLoopEndFrame;

// write one silent buffer
ExtAudioFileWrite(outFile, bufferFrames, writeBuffer);

while (frameCount < lastFrame){

    // how many frames do we need to get
    if (lastFrame - frameCount > bufferFrames)
        framesToGet = bufferFrames;
    else
        framesToGet = lastFrame - frameCount;

    // get dem frames
    err = theBigOlCallback((void*)&allRenderData,
                            NULL, NULL, 1,
                           framesToGet, writeBuffer);

    // write to output file
    ExtAudioFileWrite(outFile, framesToGet, writeBuffer);

    frameCount += framesToGet;
}

// write one trailing silent buffer
memset(writeBuffer->mBuffers[0].mData, 0, bufferBytes);
memset(writeBuffer->mBuffers[1].mData, 0, bufferBytes);
processLimiterInPlace8p24(limiter, writeBuffer->mBuffers[0].mData, writeBuffer->mBuffers[1].mData, bufferFrames);
ExtAudioFileWrite(outFile, bufferFrames, writeBuffer);

err = ExtAudioFileDispose(outFile);

pcm帧已正确创建，但ExtAudioFileWrite在第二次/第三次调用时失败。

The pcm frames are properly created, but ExtAudioFileWrite fails the 2nd/3rd time it is called.

任何想法？谢谢！

推荐答案

我遇到了一个非常类似的问题，我试图使用扩展音频文件服务来传输PCM声音到了iPad上的m4a文件2.除了每次调用ExtAudioFileWrite都返回错误代码-66567（kExtAudioFileError_MaxPacketSizeUnknown）之外，一切似乎都有效。我最终找到的修复方法是将Codec Manufacturer设置为软件而不是硬件。所以放置

I had a very similar problem where I was attempting to use Extended Audio File Services in order to stream PCM sound into an m4a file on an iPad 2. Everything appeared to work except that every call to ExtAudioFileWrite returned the error code -66567 (kExtAudioFileError_MaxPacketSizeUnknown). The fix I eventually found was to set the "Codec Manufacturer" to software instead of hardware. So place

UInt32 codecManf = kAppleSoftwareAudioCodecManufacturer;
ExtAudioFileSetProperty(FileToWrite, kExtAudioFileProperty_CodecManufacturer, sizeof(UInt32), &codecManf);

。

这将使我相信Apple的硬件编解码器只能支持非常特定的编码，但软件编解码器可以更可靠地执行您想要的操作。在我的情况下，m4a的软件编解码器转换比将完全相同的文件写入LPCM格式要长50％。

This would lead me to believe that Apple's hardware codecs can only support very specific encoding, but the software codecs can more reliably do what you want. In my case, the software codec translation to m4a takes 50% longer than writing the exact same file to LPCM format.

有没有人知道Apple是否指定了某些地方的音频编解码器硬件有能力吗？似乎软件工程师正在玩这个长达数小时的猜谜游戏，即为客户端设置AudioStreamBasicDescription和AudioChannelLayout中的~20个参数，并将文件设置为每个可能的排列，直到某些工作正常...

Does anyone know whether Apple specifies somewhere what their audio codec hardware is capable of? It seems that software engineers are stuck playing the hours-long guessing game of setting the ~20 parameters in the AudioStreamBasicDescription and AudioChannelLayout for the client and for the file to every possible permutation until something works...

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