Question

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。编码同步地在后台线程中进行，而不是实时进行。

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没有错误代码。

以下是相关代码：

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);

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

有什么想法吗？谢谢！

Answer 1

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将PCM声音流式传输到iPad 2上的m4a文件中。除了每次调用ExtAudioFileWrite都返回错误代码-66567之外，一切似乎都有效（kExtAudioFileError_MaxPacketSizeUnknown）。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

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

在您设置客户端数据格式之前。

这会让我相信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加可靠地执行您想要的操作。在我的情况下，软件编解码器转换为m4a所需的时间比将完全相同的文件写入LPCM格式长50％。

有谁知道Apple是否指定了音频编解码器硬件的功能？似乎软件工程师一直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，直到有效为止......

ExtAudioFileWrite到m4a / aac在双核设备上失败（ipad 2，iphone 4s）

1 个答案: