Question

我已使用AudioBufferList功能将音频文件读入ExtAudioFileRead。
这是音频的ASBD：

AudioStreamBasicDescription importFormat;

importFormat.mFormatID          = kAudioFormatLinearPCM;
importFormat.mFormatFlags       = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
importFormat.mBytesPerPacket    = 4;
importFormat.mFramesPerPacket   = 1;
importFormat.mBytesPerFrame     = 4;
importFormat.mChannelsPerFrame  = 2;
importFormat.mBitsPerChannel    = 16;
importFormat.mSampleRate = [[AVAudioSession sharedInstance] sampleRate];

所以我们得到了两个通道的交错音频，每个通道有16位符号int AudioBufferList init：

UInt32 *audioData = (UInt32 *) calloc (totalFramesInFile, sizeof (UInt32));

AudioBufferList *bufferList;
bufferList = (AudioBufferList *) malloc (sizeof (AudioBufferList));

// buffers amount is 1 because audio is interleaved
bufferList->mNumberBuffers = 1;

bufferList->mBuffers[0].mNumberChannels  = 2;
bufferList->mBuffers[0].mDataByteSize    = totalFramesInFile * sizeof(UInt32);
bufferList->mBuffers[0].mData            = audioData;

阅读缓冲区：

CheckError(ExtAudioFileRead (
                             audioFileObject,
                             &numberOfPacketsToRead,
                             bufferList), "error ExtAudioFileRead");

audioFileObject是ExtAudioFileRef的实例，它是在代码中启动的，我没有在此处粘贴以节省空间。
我想要完成的是修改渲染回调中的音频样本。

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


    ViewController *view = (__bridge ViewController *) inRefCon;

    soundStruct *soundStruct = (soundStruct *) &view->mys;

    SInt64            frameTotalForSound        = soundStruct->frameCount;

    soundStruct->isPlaying = true;

    UInt32 *audioData   = soundStruct->audioData;

    UInt32 sampleNumber = soundStruct->sampleNumber;

    for( int i = 0; i < ioData->mNumberBuffers; i++){

        AudioBuffer buffer = ioData->mBuffers[i];
        UInt32 *frameBuffer = buffer.mData;

        for(UInt32 frame = 0; frame < inNumberFrames; frame++) {

            // here I fill the buffer with my audio data.
            // i need to get left and right channel samples 
            // from  audioData[sampleNumber], modify them
            // and write into frameBuffer 

            frameBuffer[frame] = audioData[sampleNumber];

            sampleNumber++;

            if(sampleNumber > frameTotalForSound) {
                soundStruct->isPlaying = false;
                AudioOutputUnitStop(soundStruct->outputUnit);
            }
        }
    }

    soundStruct->sampleNumber = sampleNumber;

    return noErr;

}

是否可以从UInt32音频数据阵列中获取Sint16左右声道样本？

Answer 1

让this.wrongLocation.add(graphics);和audioData都为frameBuffer s：

SInt16

您的缓冲区大小计算应为SInt16 *audioData; // ... SInt16 *frameBuffer; soundStruct`或添加类型转换。

然后您可以像这样访问交错的样本：

n * 2 * sizeof(SInt16) and you'll either need to change

Answer 2

@Rhythmic Fistman，非常感谢 - 它有所帮助。
我无法设置frameBuffer以此方式工作。声音在输出处失真。我想这是因为AudioUnit需要一帧中的两个通道数据。或许还有其他解释。
这是我修改的代码，希望它能帮到某人：

audioData init：

SInt16 *audioData = (SInt16 *) malloc (sizeof(SInt16) * totalFramesInFile * 2);

修改了渲染回调：

OSStatus MyCallback (void *inRefCon,
             AudioUnitRenderActionFlags *ioActionFlags,
             const AudioTimeStamp *inTimeStamp,
             UInt32 inBusNumber,
             UInt32 inNumberFrames,
             AudioBufferList *ioData)
{
    ViewController *view = (__bridge ViewController *) inRefCon;

    soundStruct *soundStruct  = (soundStruct *) &view->mys;

    SInt64 frameTotalForSound = soundStruct->frameCount;

    soundStruct->isPlaying = true;

    SInt16 *audioData   = soundStruct->audioData;

    UInt32 sampleNumber = soundStruct->sampleNumber;

    for( int i = 0; i < ioData->mNumberBuffers; i++){
        AudioBuffer buffer = ioData->mBuffers[i];
        SInt16 *frameBuffer = (SInt16*) ioData->mBuffers[0].mData;

        for(UInt32 frame = 0; frame < inNumberFrames * 2; frame+=2) {

            /* .. some samples modification code .. */

            // left channel
            frameBuffer[frame] = audioData[sampleNumber];
            // right channel
            frameBuffer[frame + 1] = audioData[sampleNumber + 1];

            sampleNumber +=2;

            if(sampleNumber > frameTotalForSound * 2) {
                soundStruct->isPlaying = false;
                AudioOutputUnitStop(soundStruct->outputUnit);
            }
        }
    }

    soundStruct->sampleNumber = sampleNumber;
    return noErr;
}

ios Core音频：如何从带有交错音频的AudioBuffer中获取样本

2 个答案: