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copied!<pre><code>- (void)modifySpeedOf:(CFURLRef)inputURL byFactor:(float)factor andWriteTo:(CFURLRef)outputURL { ExtAudioFileRef inputFile = NULL; ExtAudioFileRef outputFile = NULL; AudioStreamBasicDescription destFormat; destFormat.mFormatID = kAudioFormatLinearPCM; destFormat.mFormatFlags = kAudioFormatFlagsCanonical; destFormat.mSampleRate = 44100 * factor; destFormat.mBytesPerPacket = 2; destFormat.mFramesPerPacket = 1; destFormat.mBytesPerFrame = 2; destFormat.mChannelsPerFrame = 1; destFormat.mBitsPerChannel = 16; destFormat.mReserved = 0; ExtAudioFileCreateWithURL(outputURL, kAudioFileCAFType, &destFormat, NULL, kAudioFileFlags_EraseFile, &outputFile); ExtAudioFileOpenURL(inputURL, &inputFile); //find out how many frames is this file long SInt64 length = 0; UInt32 dataSize2 = (UInt32)sizeof(length); ExtAudioFileGetProperty(inputFile, kExtAudioFileProperty_FileLengthFrames, &dataSize2, &length); SInt16 *buffer = (SInt16*)malloc(kBufferSize * sizeof(SInt16)); UInt32 totalFramecount = 0; AudioBufferList bufferList; bufferList.mNumberBuffers = 1; bufferList.mBuffers[0].mNumberChannels = 1; bufferList.mBuffers[0].mData = buffer; // pointer to buffer of audio data bufferList.mBuffers[0].mDataByteSize = kBufferSize * sizeof(SInt16); // number of bytes in the buffer while(true) { UInt32 frameCount = kBufferSize * sizeof(SInt16) / 2; // Read a chunk of input ExtAudioFileRead(inputFile, &frameCount, &bufferList); totalFramecount += frameCount; if (!frameCount || totalFramecount >= length) { //termination condition break; } ExtAudioFileWrite(outputFile, frameCount, &bufferList); } free(buffer); ExtAudioFileDispose(inputFile); ExtAudioFileDispose(outputFile); } </code></pre> <p>it will change pitch based on factor</p>

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