How to reverse an audio file?

Question

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?

Answer 1

Kiran's answer in Swift 2.2:

    let forwardAudioURL: NSURL = ... // wherever your original audio is
    let reversedAudioURL: NSURL = ... // wherever you want the reversed file to go

    // Load forward audio into originalAudioFile
    var originalAudioFile: AudioFileID = nil
    let possibleError1 = AudioFileOpenURL(forwardAudioURL,
                                          AudioFilePermissions.ReadPermission,
                                          0,
                                          &originalAudioFile)

    // Load the size in bytes of the original audio into originalAudioSize variable
    var originalAudioSize: Int64 = 0
    var propertySize: UInt32 = 8
    let possibleError2 = AudioFileGetProperty(originalAudioFile,
                                              kAudioFilePropertyAudioDataByteCount,
                                              &propertySize,
                                              &originalAudioSize)

    if possibleError1 != 0 || possibleError2 != 0 {
        // Handle errors if you want
    }

    // Set up file that the reversed audio will be loaded into
    var reversedAudioFile: AudioFileID = nil
    var format = AudioStreamBasicDescription()
    format.mSampleRate = 16000
    format.mFormatID = kAudioFormatLinearPCM
    format.mChannelsPerFrame = 1
    format.mFramesPerPacket = 1
    format.mBitsPerChannel = 16
    format.mBytesPerPacket = 2
    format.mBytesPerFrame = 2
    AudioFileCreateWithURL(reversedAudioURL,
                           kAudioFileCAFType,
                           &format,
                           AudioFileFlags.EraseFile,
                           &reversedAudioFile)

    // Read data into the reversedAudioFile
    var readPoint: Int64 = originalAudioSize
    var writePoint: Int64 = 0
    var buffer: Int16 = 0
    while readPoint > 0 {
        var bytesToRead: UInt32 = 2;
        AudioFileReadBytes(originalAudioFile,
                           false,
                           readPoint,
                           &bytesToRead,
                           &buffer)
        AudioFileWriteBytes(reversedAudioFile,
                            false,
                            writePoint,
                            &bytesToRead,
                            &buffer)
        writePoint += 2
        readPoint -= 2
    }
    AudioFileClose(originalAudioFile)
    AudioFileClose(reversedAudioFile)