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Convert AVAudioPCMBuffer to NSData and back

How to convert AVAudioPCMBuffer to NSData? If it should be done as

let data = NSData(bytes: buffer.floatChannelData, length: bufferLength)

then how to calculate bufferLength?

And how to convert NSData to AVAudioPCMBuffer?

like image 658
Shmidt Avatar asked Jan 20 '15 15:01

Shmidt


2 Answers

Buffer length is frameCapacity * bytesPerFrame. Here are functions that can do conversion between NSData and AVAudioPCMBuffer.

extension AVAudioPCMBuffer {
    func data() -> Data {
        let channelCount = 1  // given PCMBuffer channel count is 1
        let channels = UnsafeBufferPointer(start: self.floatChannelData, count: channelCount)
        let ch0Data = NSData(bytes: channels[0], length:Int(self.frameCapacity * self.format.streamDescription.pointee.mBytesPerFrame))
        return ch0Data as Data
    }
}

func toPCMBuffer(data: NSData) -> AVAudioPCMBuffer? {
    let audioFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 8000, channels: 1, interleaved: false)!  // given NSData audio format
    guard let PCMBuffer = AVAudioPCMBuffer(pcmFormat: audioFormat, frameCapacity: UInt32(data.length) / audioFormat.streamDescription.pointee.mBytesPerFrame) else {
        return nil
    }
    PCMBuffer.frameLength = PCMBuffer.frameCapacity
    let channels = UnsafeBufferPointer(start: PCMBuffer.floatChannelData, count: Int(PCMBuffer.format.channelCount))
    data.getBytes(UnsafeMutableRawPointer(channels[0]) , length: data.length)
    return PCMBuffer
}
like image 175
Rod Chen Avatar answered Nov 01 '22 17:11

Rod Chen


Copying the buffers is much easier if you copy via the audioBufferList API's. This also works no matter what the format is of the actual buffer.

extension Data {
    init(buffer: AVAudioPCMBuffer, time: AVAudioTime) {
        let audioBuffer = buffer.audioBufferList.pointee.mBuffers
        self.init(bytes: audioBuffer.mData!, count: Int(audioBuffer.mDataByteSize))
    }

    func makePCMBuffer(format: AVAudioFormat) -> AVAudioPCMBuffer? {
        let streamDesc = format.streamDescription.pointee
        let frameCapacity = UInt32(count) / streamDesc.mBytesPerFrame
        guard let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: frameCapacity) else { return nil }

        buffer.frameLength = buffer.frameCapacity
        let audioBuffer = buffer.audioBufferList.pointee.mBuffers

        withUnsafeBytes { (bufferPointer) in
            guard let addr = bufferPointer.baseAddress else { return }
            audioBuffer.mData?.copyMemory(from: addr, byteCount: Int(audioBuffer.mDataByteSize))
        }

        return buffer
    }
}
like image 35
Brian King Avatar answered Nov 01 '22 17:11

Brian King