Avaudiocompressedbuffer to Uint8 Array and Vice Versa

AVAudioCompressedBuffer to UInt8 array and vice versa

This is what I ended up doing.

The main thing was setting byteLength and packetCount on the second AVAudioCompressedBuffer.

iLBC has a fixed frame size (304 bits per block for 20ms frames)

304 * 50 = 15200 = 15.2 kbit/s

AVAudioNodeTapBlock for an AVAudioInputNode fires every 100ms.

byteLength = 304bits / 8 = 38bytes

packetCount = 5

Which will result in 5 * 38 * 10 * 8 = 15200 = 15.2 kbit/s.

The code below shows everything written out.

So, what happens is

1) Convert AVAudioPCMBuffer from microphone to AVAudioCompressedBuffer (iLBC)

2) Convert AVAudioCompressedBuffer (iLBC) to [UInt8] (5 * 38 = 190 bytes).

3) Convert [UInt8] to AVAudioCompressedBuffer (iLBC)

4) Convert AVAudioCompressedBuffer (iLBC) to AVAudioPCMBuffer

5) Play AVAudioPCMBuffer

// Compress to iLBC
let packetCapacity = 5
let maximumPacketSize = 38
let capacity = packetCapacity * maximumPacketSize // 190

var descriptor = AudioStreamBasicDescription.init(mSampleRate: 8000, mFormatID: kAudioFormatiLBC, mFormatFlags: 0, mBytesPerPacket: 0, mFramesPerPacket: 0, mBytesPerFrame: 0, mChannelsPerFrame: 1, mBitsPerChannel: 0, mReserved: 0)
let ilbcformat = AVAudioFormat.init(streamDescription: &descriptor)

let compressor: AVAudioConverter = AVAudioConverter.init(from: self.format!, to: ilbcformat)!
let inputBlock : AVAudioConverterInputBlock = { inNumPackets, outStatus in
    outStatus.pointee = AVAudioConverterInputStatus.haveData
    return buffer
}
let compressedBuffer: AVAudioCompressedBuffer = AVAudioCompressedBuffer(format: ilbcformat, packetCapacity: 5, maximumPacketSize: 38)
compressor.convert(to: compressedBuffer, error: nil, withInputFrom: inputBlock)

// Convert to Bytes
let compressedBufferPointer = compressedBuffer.data.bindMemory(to: UInt8.self, capacity: 190)
var compressedBytes: [UInt8] = [UInt8].init(repeating: 0, count: 190)
compressedBufferPointer.withMemoryRebound(to: UInt8.self, capacity: 190) { sourceBytes in
    compressedBytes.withUnsafeMutableBufferPointer {
        $0.baseAddress!.initialize(from: sourceBytes, count: 190)
    }
}

// Convert to buffer
let compressedBuffer2: AVAudioCompressedBuffer = AVAudioCompressedBuffer.init(format: ilbcformat, packetCapacity: 5, maximumPacketSize: 38)
compressedBuffer2.byteLength = 190
compressedBuffer2.packetCount = 5
compressedBytes.withUnsafeMutableBufferPointer {
    compressedBuffer2.data.copyMemory(from: $0.baseAddress!, byteCount: 190)
}

// Uncompress to PCM
let uncompressor: AVAudioConverter = AVAudioConverter.init(from: ilbcformat, to: self.format!)!
let inputBlock2 : AVAudioConverterInputBlock = { inNumPackets, outStatus in
    outStatus.pointee = AVAudioConverterInputStatus.haveData
    return compressedBuffer2
}
let uncompressedBuffer: AVAudioPCMBuffer = AVAudioPCMBuffer.init(pcmFormat: self.format!, frameCapacity: 4410)!
uncompressor.convert(to: uncompressedBuffer, error: nil, withInputFrom: inputBlock2)

// Play Buffer
self.player.scheduleBuffer(uncompressedBuffer)

Decode AAC to PCM format using AVAudioConverter Swift

There were a few problems with your attempt:

1. you're not setting the multiple packet descriptions when you convert data -> AVAudioCompressedBuffer. You need to create them, as AAC packets are of variable size. You can either copy them from the original AAC buffer, or parse them from your data by hand (ouch) or by using the AudioFileStream api.

2. you re-create your AVAudioConverters over and over again - once for each buffer, throwing away their state. e.g. the AAC encoder for its own personal reasons needs to add 2112 frames of silence before it can get around to reproducing your audio, so recreating the converter gets you a whole lot of silence.

3. you present the same buffer over and over to the AVAudioConverter's input block. You should only present each buffer once.

4. the bit rate of 32000 didn't work (for me)

That's all I can think of right now. Try the following modifications to your code instead which you now call like so:

(p.s. I changed some of the mono to stereo so I could play the round trip buffers on my mac, whose microphone input is strangely stereo - you might need to change it back)

(p.p.s there's obviously some kind of round trip / serialising/deserialising attempt going on here, but what exactly are you trying to do? do you want to stream AAC audio from one device to another? because it might be easier to let another API like AVPlayer play the resulting stream instead of dealing with the packets yourself)

let aacBuffer = AudioBufferConverter.convertToAAC(from: buffer, error: nil)!
let data = Data(bytes: aacBuffer.data, count: Int(aacBuffer.byteLength))
let packetDescriptions = Array(UnsafeBufferPointer(start: aacBuffer.packetDescriptions, count: Int(aacBuffer.packetCount)))
let aacReverseBuffer = AudioBufferConverter.convertToAAC(from: data, packetDescriptions: packetDescriptions)!
// was aacBuffer2
let pcmReverseBuffer = AudioBufferConverter.convertToPCM(from: aacReverseBuffer, error: nil)

class AudioBufferFormatHelper {

    static func PCMFormat() -> AVAudioFormat? {
        return AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 44100, channels: 1, interleaved: false)
    }

    static func AACFormat() -> AVAudioFormat? {

        var outDesc = AudioStreamBasicDescription(
            mSampleRate: 44100,
            mFormatID: kAudioFormatMPEG4AAC,
            mFormatFlags: 0,
            mBytesPerPacket: 0,
            mFramesPerPacket: 0,
            mBytesPerFrame: 0,
            mChannelsPerFrame: 1,
            mBitsPerChannel: 0,
            mReserved: 0)
        let outFormat = AVAudioFormat(streamDescription: &outDesc)
        return outFormat
    }
}

class AudioBufferConverter {
    static var lpcmToAACConverter: AVAudioConverter! = nil

    static func convertToAAC(from buffer: AVAudioBuffer, error outError: NSErrorPointer) -> AVAudioCompressedBuffer? {

        let outputFormat = AudioBufferFormatHelper.AACFormat()
        let outBuffer = AVAudioCompressedBuffer(format: outputFormat!, packetCapacity: 8, maximumPacketSize: 768)

        //init converter once
        if lpcmToAACConverter == nil {
            let inputFormat = buffer.format

            lpcmToAACConverter = AVAudioConverter(from: inputFormat, to: outputFormat!)
//            print("available rates \(lpcmToAACConverter.applicableEncodeBitRates)")
//          lpcmToAACConverter!.bitRate = 96000
            lpcmToAACConverter.bitRate = 32000    // have end of stream problems with this, not sure why
        }

        self.convert(withConverter:lpcmToAACConverter, from: buffer, to: outBuffer, error: outError)

        return outBuffer
    }

    static var aacToLPCMConverter: AVAudioConverter! = nil

    static func convertToPCM(from buffer: AVAudioBuffer, error outError: NSErrorPointer) -> AVAudioPCMBuffer? {

        let outputFormat = AudioBufferFormatHelper.PCMFormat()
        guard let outBuffer = AVAudioPCMBuffer(pcmFormat: outputFormat!, frameCapacity: 4410) else {
            return nil
        }

        //init converter once
        if aacToLPCMConverter == nil {
            let inputFormat = buffer.format

            aacToLPCMConverter = AVAudioConverter(from: inputFormat, to: outputFormat!)
        }

        self.convert(withConverter: aacToLPCMConverter, from: buffer, to: outBuffer, error: outError)

        return outBuffer
    }

    static func convertToAAC(from data: Data, packetDescriptions: [AudioStreamPacketDescription]) -> AVAudioCompressedBuffer? {

        let nsData = NSData(data: data)
        let inputFormat = AudioBufferFormatHelper.AACFormat()
        let maximumPacketSize = packetDescriptions.map { $0.mDataByteSize }.max()!
        let buffer = AVAudioCompressedBuffer(format: inputFormat!, packetCapacity: AVAudioPacketCount(packetDescriptions.count), maximumPacketSize: Int(maximumPacketSize))
        buffer.byteLength = UInt32(data.count)
        buffer.packetCount = AVAudioPacketCount(packetDescriptions.count)

        buffer.data.copyMemory(from: nsData.bytes, byteCount: nsData.length)
        buffer.packetDescriptions!.pointee.mDataByteSize = UInt32(data.count)
        buffer.packetDescriptions!.initialize(from: packetDescriptions, count: packetDescriptions.count)

        return buffer
    }

    private static func convert(withConverter: AVAudioConverter, from sourceBuffer: AVAudioBuffer, to destinationBuffer: AVAudioBuffer, error outError: NSErrorPointer) {
        // input each buffer only once
        var newBufferAvailable = true

        let inputBlock : AVAudioConverterInputBlock = {
            inNumPackets, outStatus in
            if newBufferAvailable {
                outStatus.pointee = .haveData
                newBufferAvailable = false
                return sourceBuffer
            } else {
                outStatus.pointee = .noDataNow
                return nil
            }
        }

        let status = withConverter.convert(to: destinationBuffer, error: outError, withInputFrom: inputBlock)
        print("status: \(status.rawValue)")
    }
}

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