WASAPI capture in F#

wasapi_capture.fs

open System.Runtime.InteropServices
open NAudio.CoreAudioApi
    
module NativeMethods =
    [<DllImport("api-ms-win-core-synch-l1-2-0.dll")>]
    extern System.IntPtr CreateEvent(System.IntPtr lpEventAttributes, bool bManualReset, bool bInitialState, System.IntPtr lpName)

    [<DllImport("api-ms-win-core-handle-l1-1-0.dll")>]
    extern bool CloseHandle(System.IntPtr hObject)

    [<DllImport("api-ms-win-core-synch-l1-2-0.dll")>]
    extern int WaitForSingleObject(System.IntPtr hEvent, int milliseconds)

[<EntryPoint>]
let main args =
    // デフォルトのキャプチャデバイス取得
    let deviceEnumerator = new MMDeviceEnumerator()
    let device = (DataFlow.Capture, Role.Console) |> deviceEnumerator.GetDefaultAudioEndpoint
    printfn "Default Capture Device: %s" device.FriendlyName
  
      // AudioClient取得
    let client = device.AudioClient
    
    // 初期化
    (
        AudioClientShareMode.Shared,
        AudioClientStreamFlags.EventCallback,
        client.DefaultDevicePeriod,
        client.DefaultDevicePeriod,
        (48000, 16, 2) |> NAudio.Wave.WaveFormat,
        System.Guid.Empty
    ) |> client.Initialize

    // バッファイベントを登録する
    let frameEventWaitHandle = (System.IntPtr.Zero, false, false, System.IntPtr.Zero) |> NativeMethods.CreateEvent
    frameEventWaitHandle |> client.SetEventHandle

    // バッファサイズを取得する
    let bufsize = client.BufferSize

    // AudioCaptureClient取得
    let captureClient = client.AudioCaptureClient

    // キャプチャ開始
    () |> client.Start

    let mutable stop = false
 
    async{
        // Enterキーが押されたら終了
        () |> stdin.ReadLine |> ignore
        printfn "enter key pressed"
        stop <- true
    } |> Async.StartAsTask |> ignore
    
    while not stop do
        // バッファがいっぱいになるまで待つ
        (frameEventWaitHandle, -1) |> NativeMethods.WaitForSingleObject |> ignore
                
        // バッファ取得
        let mutable numFrameToRead = 0
        let mutable bufferFlags = AudioClientBufferFlags.None
        let p = captureClient.GetBuffer(&numFrameToRead, &bufferFlags)

        match bufferFlags with
        | AudioClientBufferFlags.None -> 
            printfn "numFrameToRead: %d" numFrameToRead

            //////////////
            // 何かする //
            //////////////
        | _ -> ()

        // バッファ解放
        numFrameToRead |> captureClient.ReleaseBuffer
    done

    // キャプチャ停止
    () |> client.Stop

    // 後始末
    frameEventWaitHandle |> NativeMethods.CloseHandle |> ignore
    () |> client.Dispose
    () |> device.Dispose
    () |> deviceEnumerator.Dispose
    0