Convert AVAudioPCMBuffer to NSData and back

Question

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?

score 35 · Accepted Answer · edited Nov 15 '21 at 15:29

35

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
}

edited Nov 15 '21 at 15:29

Eric

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answered May 24 '15 at 15:29

Rod Chen

482
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9

Me too @Massimo. – Brennan Mar 10 '17 at 19:44
4

I succeeded in transforming `NSData` in `AVAudioPCMBuffer` (I did not need the reverse, so don't have that code): http://pastebin.com/raw/m5c74FPA – Massimo Mar 13 '17 at 08:32
1

@Massimo how to reverse it, means AVAudioPCMBuffer to 16 bit NSData ? – Dipen Chudasama Aug 30 '17 at 12:37
objective-c answer? – Billy Caruso Mar 16 '19 at 01:53
2

For Swift 4, replace `streamDescription.memory` with `streamDescription.pointee`. – Avi Aug 06 '19 at 07:21
2

Hi is it ok to use `.floatChannelData` when the data is actually int16? – ch271828n Sep 17 '20 at 07:55

score 13 · Answer 2 · edited Mar 02 '20 at 16:47

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
    }
}

To avoid `'withUnsafeBytes' is deprecated: use 'withUnsafeBytes(_: (UnsafeRawBufferPointer) throws -> R) rethrows -> R'` warning with _Swift 5_, you can pass `addr.baseAddress` to `copyMemory` function instead of `addr`. — aleksmutlu, Nov 07 '19 at 09:09

Convert AVAudioPCMBuffer to NSData and back

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