如何反转音频文件? [英] How to reverse an audio file?

问题描述

我想在 iOS 上反转现有的音频文件(例如 WAV、CAF 等).关于如何实现这一目标的任何建议?开源库?

I'd like to reverse an existing audio file (e.g. WAV, CAF, ...) on iOS. Any suggestions on how to achieve this? Open-source libraries?

推荐答案

我已经开发了一个示例应用程序，它记录用户所说的内容并向后播放.我已经使用 CoreAudio 来实现这一点.链接到应用代码.

I have worked on a sample app, which records what user says and plays them backwards. I have used CoreAudio to achieve this. Link to app code.

因为每个样本的大小为 16 位(2 字节)(单声道).您可以通过在记录结束时开始向后读取，将每个样本复制到不同的缓冲区中，从而一次加载每个样本.当您到达数据的开头时，您已反转数据并且播放将反转.

As each sample is 16-bits in size(2 bytes)(mono channel). You can load each sample at a time by copying it into a different buffer by starting at the end of the recording and reading backwards. When you get to the start of the data you have reversed the data and playing will be reversed.

    // set up output file
AudioFileID outputAudioFile;

AudioStreamBasicDescription myPCMFormat;
myPCMFormat.mSampleRate = 16000.00;
myPCMFormat.mFormatID = kAudioFormatLinearPCM ;
myPCMFormat.mFormatFlags =  kAudioFormatFlagsCanonical;
myPCMFormat.mChannelsPerFrame = 1;
myPCMFormat.mFramesPerPacket = 1;
myPCMFormat.mBitsPerChannel = 16;
myPCMFormat.mBytesPerPacket = 2;
myPCMFormat.mBytesPerFrame = 2;


AudioFileCreateWithURL((__bridge CFURLRef)self.flippedAudioUrl,
                       kAudioFileCAFType,
                       &myPCMFormat,
                       kAudioFileFlags_EraseFile,
                       &outputAudioFile);
// set up input file
AudioFileID inputAudioFile;
OSStatus theErr = noErr;
UInt64 fileDataSize = 0;

AudioStreamBasicDescription theFileFormat;
UInt32 thePropertySize = sizeof(theFileFormat);

theErr = AudioFileOpenURL((__bridge CFURLRef)self.recordedAudioUrl, kAudioFileReadPermission, 0, &inputAudioFile);

thePropertySize = sizeof(fileDataSize);
theErr = AudioFileGetProperty(inputAudioFile, kAudioFilePropertyAudioDataByteCount, &thePropertySize, &fileDataSize);

UInt32 dataSize = fileDataSize;
void* theData = malloc(dataSize);

//Read data into buffer
UInt32 readPoint  = dataSize;
UInt32 writePoint = 0;
while( readPoint > 0 )
{
    UInt32 bytesToRead = 2;

    AudioFileReadBytes( inputAudioFile, false, readPoint, &bytesToRead, theData );
    AudioFileWriteBytes( outputAudioFile, false, writePoint, &bytesToRead, theData );

    writePoint += 2;
    readPoint -= 2;
}

free(theData);
AudioFileClose(inputAudioFile);
AudioFileClose(outputAudioFile);

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