Sélection WaveIn comme source d'enregistrement

Bonjour, J'utilise le code suivant pour sélectionner la source WaveIn pour un enregistrement:

Code:

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Declare Function waveInOpen Lib "winmm.dll" Alias "waveInOpen" (ByVal lphWaveIn As Long, ByVal uDeviceID As Long, ByVal lpFormat As WAVEFORMAT, ByVal dwCallback As Long, ByVal dwInstance As Long, ByVal dwFlags As Long) As Long
  Private Format As WAVEFORMAT
  Structure WAVEFORMAT
    Dim wFormatTag As Integer
    Dim nChannels As Integer
    Dim nSamplesPerSec As Long
    Dim nAvgBytesPerSec As Long
    Dim nBlockAlign As Integer
    Dim wBitsPerSample As Integer
    Dim cbSize As Integer
  End Structure
  Structure WAVEHDR
    Dim lpData As Long
    Dim dwBufferLength As Long
    Dim dwBytesRecorded As Long
    Dim dwUser As Long
    Dim dwFlags As Long
    Dim dwLoops As Long
    Dim lpNext As Long
    Dim Reserved As Long
  End Structure
  Public Structure WaveFormatEx
    Public FormatTag As Int16
    Public Channels As Int16
    Public SamplesPerSec As Int32
    Public AvgBytesPerSec As Int32
    Public BlockAlign As Int16
    Public BitsPerSample As Int16
    Public ExtraDataSize As Int16
  End Structure
 
  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Format = New WaveFormat()
    Format.nChannels = 1
    Format.nSamplesPerSec = 44100
    Format.nAvgBytesPerSec = 44100
    Format.nBlockAlign = 1
    Format.wBitsPerSample = 8
    Format.cbSize = 0
    Dim hWaveIn As Long
    Dim rc As Long = waveInOpen(hWaveIn, -1, Format, 0, 0, 0)
  End Sub

L'application retourne une AccessViolationException à la ligne

Code:

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Dim rc As Long = waveInOpen(hWaveIn, -1, Format, 0, 0, 0)

Quelqu'un peut-il m'indiquer comment faire ?
Merci
JoceM