AVAudioCompressedBuffer 到 UInt8 数组，反之亦然

我想知道如何获取 AVAudioCompressedBuffer 的字节，然后 从字节重建 AVAudioCompressedBuffer。

下面的代码采用 AVAudioPCMBuffer，使用 AVAudioConverter 将其压缩为 AVAudioCompressedBuffer (iLBC) 并获取字节，然后将字节转换回 AVAudioCompressedBuffer (iLBC) 并解压缩回 AVAudioPCMBuffer 并播放缓冲区。将 AVAudioCompressedBuffer 转换为字节并返回时出现问题。如果我跳过此转换，音频将按预期播放。

我什至可以匹配compressedBuffer和compressedBuffer2的内容，这让我相信获取字节的机制并不完全正确。

// Do iLBC Compression
let compressedBuffer: AVAudioCompressedBuffer = self.compress(inBuffer: buffer)
// packetCapacity: 4, maximumPacketSize: 38
// self.player.scheduleBuffer(self.uncompress(inBuffer: compressedBuffer)) // This works perfectly

// Convert Buffer to Byte Array
let pointer1: UnsafeMutablePointer = compressedBuffer.data.bindMemory(to: UInt8.self, capacity: 152)
var audioByteArray = [UInt8](repeating: 0, count: 152)
pointer1.withMemoryRebound(to: UInt8.self, capacity: 152) { srcByteData in
    audioByteArray.withUnsafeMutableBufferPointer {
        $0.baseAddress!.initialize(from: srcByteData, count: 152)
    }
}

// Convert Byte Array to Buffer
let compressedBuffer2: AVAudioCompressedBuffer = AVAudioCompressedBuffer(format: AVAudioFormat.init(streamDescription: &self.descriptor)!, packetCapacity: 4, maximumPacketSize: 38)
let destination = compressedBuffer2.data
audioByteArray.withUnsafeBufferPointer {
    let src = UnsafeRawPointer($0.baseAddress!).bindMemory(to: UInt8.self, capacity: 152)
    destination.copyMemory(from: src, byteCount: 152)
}

// Do iLBC Decompression
let uncompressedBuffer: AVAudioPCMBuffer = self.uncompress(inBuffer: compressedBuffer2)
// Works perfectly with inBuffer: compressedBuffer

// Play Buffer
self.player.scheduleBuffer(uncompressedBuffer)
// Plays fine when 'let uncompressedBuffer: AVAudioPCMBuffer = self.uncompress(inBuffer: compressedBuffer)'

压缩和解压缩功能

let format = AVAudioFormat.init(commonFormat: AVAudioCommonFormat.pcmFormatFloat32, sampleRate: 16000, channels: 1, interleaved: false)
var compressedFormatDescriptor = AudioStreamBasicDescription(mSampleRate: 8000, mFormatID: kAudioFormatiLBC, mFormatFlags: 0, mBytesPerPacket: 0, mFramesPerPacket: 0, mBytesPerFrame: 0, mChannelsPerFrame: 1, mBitsPerChannel: 0, mReserved: 0)

func compress(inBuffer : AVAudioPCMBuffer) -> AVAudioCompressedBuffer {
    let inputFormat = inBuffer.format

    let converter = AVAudioConverter(from: inputFormat, to: self.compressedFormat!)

    let outBuffer = AVAudioCompressedBuffer(format: self.compressedFormat!, packetCapacity: 4, maximumPacketSize: 38)
    let inputBlock : AVAudioConverterInputBlock = { inNumPackets, outStatus in
        outStatus.pointee = AVAudioConverterInputStatus.haveData
        return inBuffer
    }
    var error : NSError?
    converter!.convert(to: outBuffer, error: &error, withInputFrom: inputBlock)

    return outBuffer
}

func uncompress(inBuffer : AVAudioCompressedBuffer) -> AVAudioPCMBuffer {
    let inputFormat = inBuffer.format
    let outputFormat = format

    let converter = AVAudioConverter(from: inputFormat, to: outputFormat!)

    let inputBlock : AVAudioConverterInputBlock = { inNumPackets, outStatus in
        outStatus.pointee = AVAudioConverterInputStatus.haveData
        return inBuffer
    }
    var error : NSError?
    let outBuffer: AVAudioPCMBuffer = AVAudioPCMBuffer(pcmFormat: outputFormat!, frameCapacity: 1600)!
    converter!.convert(to: outBuffer, error: &error, withInputFrom: inputBlock)

    return outBuffer
}

这就是我最终所做的。
主要的事情是在第二个 AVAudioCompressedBuffer 上设置 byteLength 和 packetCount。

iLBC 具有固定的帧大小（20ms 帧每块 304 位）
304 * 50 = 15200 = 15.2 kbit/s

AVAudioInputNode 的 AVAudioNodeTapBlock 每 100 毫秒触发一次。
字节长度 = 304 位 / 8 = 38 字节
数据包计数 = 5

这将导致 5 * 38 * 10 * 8 = 15200 = 15.2 kbit/s。

下面的代码显示了所写的所有内容。
所以，发生的事情是
1) 将 AVAudioPCMBuffer 从麦克风转换为 AVAudioCompressedBuffer (iLBC)
2) 将 AVAudioCompressedBuffer (iLBC) 转换为 [UInt8]（5 * 38 = 190 字节）。
3）将[UInt8]转换为AVAudioCompressedBuffer（iLBC）
4) 将 AVAudioCompressedBuffer (iLBC) 转换为 AVAudioPCMBuffer
5) 播放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)