ExtAudioFileWrite到M4A/AAC未能上雙核設備（iPad 2的，iPhone 4S的）

Question

我寫了一個循環編碼通過我的應用程序使用的AAC擴展音頻文件服務產生的PCM音頻數據。編碼在後臺線程中同步發生，而不是實時發生。

的編碼工作完美無缺的ipad上1和iPhone 3GS/4兩者IOS 4和5然而，對於雙核設備（iPhone 4S，ipad的2）至ExtAudioFileWrite第三呼叫崩潰不具有堆棧跟蹤的編碼線程並沒有錯誤代碼。

這裏是有問題的代碼：

的數據格式

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; 
} 

呈現循環

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); 

所述PCM幀被適當地創建，但ExtAudioFileWrite失敗第二/第三時間它被稱爲。

任何想法？謝謝！

Answer 1

我有，我正在試圖使用擴展音頻文件服務，以流PCM聲音轉換成M4A文件在iPad 2似乎一切所不同的是ExtAudioFileWrite每次調用返回的錯誤代碼工作的一個非常類似的問題 - 66567（kExtAudioFileError_MaxPacketSizeUnknown）。我最終發現的解決方案是將「編解碼器製造商」設置爲軟件而不是硬件。所以，放置

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

將客戶端設置數據格式之前。

這將導致我相信，蘋果的硬件編解碼器只能支持非常特殊的編碼，但軟件編解碼器可以更可靠地做你想做的。就我而言，軟件編解碼器轉換爲m4a的時間比將完全相同的文件寫入LPCM格式的時間長50％。

有誰知道蘋果是否指定了自己的音頻編解碼器的硬件能夠某處？看來，軟件工程師被卡住打在AudioStreamBasicDescription和AudioChannelLayout客戶端和文件到每一個可能的排列直到有工作設定〜20個參數的時間長的猜謎遊戲...