使用.caf播放ExtAudioFileRead音频文件不是同步的

Question

我的应用程序对来自麦克风输入的音频进行巨大的数据处理。为了获得一个“演示模式”，我想做同样的事情，基于本地的.caf音频文件。我设法得到了音频文件。现在，我尝试使用ExtAudioFileRead读取.caf文件，然后进行数据处理。

void readFile()
{
OSStatus err = noErr;

// Audio file
NSURL *path = [[NSBundle mainBundle] URLForResource:@"output" withExtension:@"caf"];
ExtAudioFileOpenURL((__bridge CFURLRef)path, &audio->audiofile);
assert(audio->audiofile);

// File's format.
AudioStreamBasicDescription fileFormat;
UInt32 size = sizeof(fileFormat);
err = ExtAudioFileGetProperty(audio->audiofile, kExtAudioFileProperty_FileDataFormat, &size, &fileFormat);

// tell the ExtAudioFile API what format we want samples back in
//bzero(&audio->clientFormat, sizeof(audio->clientFormat));
audio->clientFormat.mSampleRate         = SampleRate;
audio->clientFormat.mFormatID           = kAudioFormatLinearPCM;
audio->clientFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
audio->clientFormat.mFramesPerPacket    = 1;
audio->clientFormat.mChannelsPerFrame   = 1;
audio->clientFormat.mBitsPerChannel     = 16;//sizeof(AudioSampleType) * 8;
audio->clientFormat.mBytesPerPacket     = 2 * audio->clientFormat.mChannelsPerFrame;
audio->clientFormat.mBytesPerFrame      = 2 * audio->clientFormat.mChannelsPerFrame;
err = ExtAudioFileSetProperty(audio->audiofile, kExtAudioFileProperty_ClientDataFormat, sizeof(audio->clientFormat), &audio->clientFormat);

// find out how many frames we need to read
SInt64 numFrames = 0;
size = sizeof(numFrames);
err = ExtAudioFileGetProperty(audio->audiofile, kExtAudioFileProperty_FileLengthFrames, &size, &numFrames);

// create the buffers for reading in data
AudioBufferList *bufferList = malloc(sizeof(AudioBufferList) + sizeof(AudioBuffer) * (audio->clientFormat.mChannelsPerFrame - 1));
bufferList->mNumberBuffers = audio->clientFormat.mChannelsPerFrame;
for (int ii=0; ii < bufferList->mNumberBuffers; ++ii)
{
    bufferList->mBuffers[ii].mDataByteSize = sizeof(float) * (int)numFrames;
    bufferList->mBuffers[ii].mNumberChannels = 1;
    bufferList->mBuffers[ii].mData = malloc(bufferList->mBuffers[ii].mDataByteSize);
}

UInt32 maxReadFrames = 1024;
UInt32 rFrames = (UInt32)numFrames;
while(rFrames > 0)
{
    UInt32 framesToRead = (maxReadFrames > rFrames) ? rFrames : maxReadFrames;
    err = ExtAudioFileRead(audio->audiofile, &framesToRead, bufferList);
    [audio processAudio:bufferList];
    if (rFrames % SampleRate == 0)
        [audio realtimeUpdate:nil];
    rFrames = rFrames - maxReadFrames;
}

// Close the file
ExtAudioFileDispose(audio->audiofile);

// destroy the buffers
for (int ii=0; ii < bufferList->mNumberBuffers; ++ii)
{
    free(bufferList->mBuffers[ii].mData);
}
free(bufferList);
bufferList = NULL;
}

很明显，有些事情我不理解，或者ExtAudioFileRead做错了，因为这段代码根本不起作用。我有两个主要问题：

1. 该文件立即播放。我的意思是，44'100个样本显然不等于1秒。我的3分钟音频文件处理在几秒钟内完成.
2. 在处理过程中，我需要更新UI。所以我有一些dispatch_sync在processaudio和realtimeUpdate。这似乎真的没有得到ExtAudioFileRead的赞赏，而且被冻结了。谢谢你的帮助。

Answer 1

您编写的代码只是从文件中读取示例，然后调用processAudio。我们将尽快完成这一工作。一旦processAudio完成，就会读取下一批示例，并再次调用processAudio。您不应该假设从音频文件(这是一个低级别和非阻塞的os调用)读取的时间与音频读取所需的时间相同。如果您想按照示例速率处理文件中的音频，您可能应该使用AUFilePlayer音频单元。这可以以正确的速度播放文件，您可以使用回调在真实的音频时间内处理示例，而不是“尽可能快”。