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
?
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
}
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
}
}
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