iOS 音频处理, AVAudioEngine

音频处理的格式有 ASBD ， AudioStreamBasicDescription

和 ASPD, AudioStreamPacketDescription

有 ASPD ，就是压缩音频，例如 mp3

let isCompressed = packetDescriptionsOrNil != nil

没有 ASPD ，就使用 ASBD, 就是非压缩音频，例如 wav

压缩音频，里面的数据不均匀，每个包含有的帧数据不等

func ParserPacketCallback(_ context: UnsafeMutableRawPointer, _ byteCount: UInt32, _ packetCount: UInt32, _ data: UnsafeRawPointer, _ packetDescriptions: Optional<UnsafeMutablePointer<AudioStreamPacketDescription>>) {
    let parser = Unmanaged<Parser>.fromOpaque(context).takeUnretainedValue()
    let packetDescriptionsOrNil: UnsafeMutablePointer<AudioStreamPacketDescription>? = packetDescriptions
    let isCompressed = packetDescriptionsOrNil != nil
    os_log("%@ - %d [bytes: %i, packets: %i, compressed: %@]", log: Parser.loggerPacketCallback, type: .debug, #function, #line, byteCount, packetCount, "\(isCompressed)")
    
    /// At this point we should definitely have a data format
    guard let dataFormat = parser.dataFormat else {
        return
    }
    
    /// Iterate through the packets and store the data appropriately
    if isCompressed {
        guard let packetDesp = packetDescriptions else {
            return
        }
        for i in 0 ..< Int(packetCount) {
            let packetDescription = packetDesp[i]
            let packetStart = Int(packetDescription.mStartOffset)
            let packetSize = Int(packetDescription.mDataByteSize)
            let packetData = Data(bytes: data.advanced(by: packetStart), count: packetSize)
            parser.packets.append((packetData, packetDescription))
        }
    } else {
        let format = dataFormat.streamDescription.pointee
        let bytesPerPacket = Int(format.mBytesPerPacket)
        for i in 0 ..< Int(packetCount) {
            let packetStart = i * bytesPerPacket
            let packetSize = bytesPerPacket
            let packetData = Data(bytes: data.advanced(by: packetStart), count: packetSize)
            parser.packets.append((packetData, nil))
        }
    }
}

本文地址：https://blog.csdn.net/dengjiangszhan/article/details/109612365