使用音频单元播放音频文件？

Question

在openframeworks和这个网站http://atastypixel.com/blog/using-remoteio-audio-unit的帮助下，我已经成功地使用audio Units将麦克风中的音频录制成音频文件。

我希望能够将文件流回音频单元并播放音频。根据Play an audio file using RemoteIO and Audio Unit的说法，我可以使用ExtAudioFileOpenURL和ExtAudioFileRead。但是，我如何播放我的缓冲区中的音频数据？

这是我目前所拥有的：

static OSStatus setupAudioFileRead() {
    //construct the file destination URL
    CFURLRef destinationURL = audioSystemFileURL();
    OSStatus status = ExtAudioFileOpenURL(destinationURL, &audioFileRef);
    CFRelease(destinationURL);

    if (checkStatus(status)) { ofLog(OF_LOG_ERROR, "ofxiPhoneSoundStream: Couldn't open file to read"); return status; }

    while( TRUE ) {
        // Try to fill the buffer to capacity.
        UInt32 framesRead = 8000;
        status = ExtAudioFileRead( audioFileRef, &framesRead, &inputBufferList );

        // error check
        if( checkStatus(status) ) { break; }

        // 0 frames read means EOF.
        if( framesRead == 0 ) { break; }

        //play audio???
    }

    return noErr;
}

Answer 1

来自作者：http://atastypixel.com/blog/using-remoteio-audio-unit/，如果你向下滚动到回放部分，尝试如下所示：

static OSStatus playbackCallback(void *inRefCon, 
                                  AudioUnitRenderActionFlags *ioActionFlags, 
                                  const AudioTimeStamp *inTimeStamp, 
                                  UInt32 inBusNumber, 
                                  UInt32 inNumberFrames, 
                                  AudioBufferList *ioData) {    
    // Notes: ioData contains buffers (may be more than one!)
    // Fill them up as much as you can. Remember to set the size value in each buffer to match how
    // much data is in the buffer.

for (int i=0; i < ioData->mNumberBuffers; i++) 
{ 
    AudioBuffer buffer = ioData->mBuffers[i];
    // copy from your whatever buffer data to output buffer
    UInt32 size = min(buffer.mDataByteSize, your buffer.size); 
    memcpy(buffer.mData, your buffer, size);
    buffer.mDataByteSize = size; // indicate how much data we wrote in the buffer

    // To test if your Audio Unit setup is working - comment out the three 
    // lines above and uncomment the for loop below to hear random noise  
    /*
    UInt16 *frameBuffer = buffer.mData;
    for (int j = 0; j < inNumberFrames; j++) {
        frameBuffer[j] = rand();
    }
    */
}
return noErr;
}

如果你只是想从麦克风录制到一个文件并回放，那么苹果的Speakhere样例可能更好用。

Answer 2

基本上是1、创建一个RemoteIO单元(参考创建RemoteIO的参考资料)；

1. 创建FilePlayer音频单元，它是读取音频文件并将文件中的音频数据提供给输出单元的专用音频单元，例如，在步骤1中创建的RemoteIO单元。要实际使用FilePlayer，需要进行大量设置(指定播放哪个文件、播放文件的哪部分等)。需要在it；
2. 上设置RemoteIO单元的kAudioUnitProperty_SetRenderCallback和kAudioUnitProperty_StreamFormat属性。第一个属性本质上是一个回调函数，RemoteIO单元从该回调函数中提取音频数据并播放。第二个属性必须根据FilePlayer支持的StreamFormat进行设置。它可以从在步骤3中设置的回调FilePlayer.
3. Define上调用的get-property函数派生而来，其中最重要的操作是请求FilePlayer呈现到回调提供的缓冲区中，为此您需要在FilePlayer.
4. Finally上调用AudioUnitRender()启动RemoteIO单元来播放文件。

上面只是对在iOS上使用音频单元播放文件的基本操作的初步概述。您可以参考Chris Adamson和Kevin Avila的Learning Core Audio了解详细信息。

Answer 3

这是一种相对简单的方法，它利用了Tasty博客中提到的音频单元。在录音回调中，您可以使用ExtAudioFileRead将来自文件的数据填充到缓冲区中，而不是使用麦克风中的数据填充缓冲区。我将尝试在下面粘贴一个示例。请注意，这只适用于.caf文件。

在start方法中，调用一个readAudio或initAudioFile函数，该函数只获取有关文件的所有信息。

- (void) start {
readAudio();
OSStatus status = AudioOutputUnitStart(audioUnit);
checkStatus(status);
}

现在，在readAudio方法中，初始化音频文件引用。

ExtAudioFileRef fileRef;

void readAudio() {
NSString * name = @"AudioFile";
NSString * source = [[NSBundle mainBundle] pathForResource:name ofType:@"caf"];
const char * cString = [source cStringUsingEncoding:NSASCIIStringEncoding];
CFStringRef str = CFStringCreateWithCString(NULL, cString, kCFStringEncodingMacRoman);
CFURLRef inputFileURL = CFURLCreateWithFileSystemPath(kCFAllocatorDefault, str, kCFURLPOSIXPathStyle, false);

AudioFileID fileID;
OSStatus err = AudioFileOpenURL(inputFileURL, kAudioFileReadPermission, 0, &fileID);
CheckError(err, "AudioFileOpenURL");


err = ExtAudioFileOpenURL(inputFileURL, &fileRef);
CheckError(err, "ExtAudioFileOpenURL");

err = ExtAudioFileSetProperty(fileRef, kExtAudioFileProperty_ClientDataFormat, sizeof(AudioStreamBasicDescription), &audioFormat);
CheckError(err, "ExtAudioFileSetProperty");
}

现在您已经有了音频数据，下一步就很简单了。在recordingCallback中，从文件而不是麦克风中读取数据。

static OSStatus recordingCallback(void *inRefCon,
                              AudioUnitRenderActionFlags *ioActionFlags,
                              const AudioTimeStamp *inTimeStamp,
                              UInt32 inBusNumber,
                              UInt32 inNumberFrames,
                              AudioBufferList *ioData) {

// Because of the way our audio format (setup below) is chosen:
// we only need 1 buffer, since it is mono
// Samples are 16 bits = 2 bytes.
// 1 frame includes only 1 sample

AudioBuffer buffer;

buffer.mNumberChannels = 1;
buffer.mDataByteSize = inNumberFrames * 2;
buffer.mData = malloc( inNumberFrames * 2 );

// Put buffer in a AudioBufferList
AudioBufferList bufferList;
bufferList.mNumberBuffers = 1;
bufferList.mBuffers[0] = buffer;

// Then:
// Obtain recorded samples
OSStatus err = ExtAudioFileRead(fileRef, &inNumberFrames, &bufferList);

// Now, we have the samples we just read sitting in buffers in bufferList
// Process the new data
[iosAudio processAudio:&bufferList];

// release the malloc'ed data in the buffer we created earlier
free(bufferList.mBuffers[0].mData);

return noErr;
}

这对我很有效。