6

我编写了一个循环，使用扩展音频文件服务将我的应用生成的 pcm 音频数据编码为 aac。编码在后台线程中同步进行，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），对 ExtAudioFileWrite 的第三次调用会使编码线程崩溃，没有堆栈跟踪和错误代码.

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 2 次/第 3 次调用时失败。

有任何想法吗？谢谢！

4

1 回答 1

18

我有一个非常相似的问题，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 返回错误代码 -66567（kExtAudioFileError_MaxPacketSizeUnknown）外，一切似乎都正常工作. 我最终找到的解决方法是将“编解码器制造商”设置为软件而不是硬件。所以放置

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

就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可靠地执行您想要的操作。就我而言，将软件编解码器转换为 m4a 比将完全相同的文件写入 LPCM 格式花费的时间要长 50%。

有谁知道苹果是否在某个地方指定了他们的音频编解码器硬件的能力？似乎软件工程师一直在玩长达数小时的猜谜游戏，即在 AudioStreamBasicDescription 和 AudioChannelLayout 中为客户端和文件设置约 20 个参数，直至出现任何可能的排列...

于 2012-03-22T18:19:14.790 回答