如何扭转音频文件？ [英] How to reverse an audio file?

问题描述

我想扭转现有的音频文件（如WAV，CAF，...）iOS上。任何建议如何实现这一目标？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

我在一个示例应用程序，它记录哪些用户说和向后播放这些工作。我已经使用CoreAudio的实现这一点。链接到应用code。

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.

由于每个样品是长度为16比特（2字节）（单信道）。可以通过开始在记录的末端和阅读向后其复制到不同的缓冲器在一个时间加载每个样品。当你到了数据的开始你已经扭转了数据和播放将发生逆转。

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);

这篇关于如何扭转音频文件？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！