VB.Net Capture Video Using avicap32.dll without UI

Question

I am trying to create an application that records a video using avicap32.dll, but without using an user interface. The sample code that I found(the only code that shows how to record a video and not just capture an image) uses an hWnd that required the handle-ID of a picture-box. Is there any way that I can circumvent this, and just connect to the driver, record and save the video?

My code below:

    Imports System
    Imports System.Runtime.InteropServices
    Public Class Recorder
        Const WM_CAP_START = &H400S
        Const WS_CHILD = &H40000000
        Const WS_VISIBLE = &H10000000

        Const WM_CAP_DRIVER_CONNECT = WM_CAP_START + 10
        Const WM_CAP_DRIVER_DISCONNECT = WM_CAP_START + 11
        Const WM_CAP_EDIT_COPY = WM_CAP_START + 30
        Const WM_CAP_SEQUENCE = WM_CAP_START + 62
        Const WM_CAP_FILE_SAVEAS = WM_CAP_START + 23

        Const WM_CAP_SET_SCALE = WM_CAP_START + 53
        Const WM_CAP_SET_PREVIEWRATE = WM_CAP_START + 52
        Const WM_CAP_SET_PREVIEW = WM_CAP_START + 50

        Const SWP_NOMOVE = &H2S
        Const SWP_NOSIZE = 1
        Const SWP_NOZORDER = &H4S
        Const HWND_BOTTOM = 1

        Declare Function capGetDriverDescriptionA Lib "avicap32.dll" (ByVal wDriverIndex As Short, ByVal lpszName As String, ByVal cbName As Integer, ByVal lpszVer As String, ByVal cbVer As Integer) As Boolean

        Declare Function capCreateCaptureWindowA Lib "avicap32.dll" (ByVal lpszWindowName As String, ByVal dwStyle As Integer, ByVal x As Integer, ByVal y As Integer, ByVal nWidth As Integer, ByVal nHeight As Short, ByVal hWnd As Integer, ByVal nID As Integer) As Integer

        Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Integer, ByVal Msg As Integer, ByVal wParam As Integer, <MarshalAs(UnmanagedType.AsAny)> ByVal lParam As Object) As Integer

        Private Shared Function ReturnDriver() As Integer 'As String
            Dim DriverName As String = Space(100)
            Dim DriverVersion As String = Space(100)
            'Dim ReturnDriverName As String = ""
            Dim DriverIndex As Integer = Nothing
            For i As Integer = 0 To 9
                If capGetDriverDescriptionA(i, DriverName, 80, DriverVersion, 80) Then
                    'lstVideoSources.Items.Add(DriverName.Trim)
                    'ReturnDriverName = DriverName.Trim
                    DriverIndex = i
                    Exit For
                End If
            Next
            Return DriverIndex
        End Function

        Public Shared Sub StartRecording()
            Dim DriverVersion As Integer = ReturnDriver()
            If SendMessage(0, WM_CAP_DRIVER_CONNECT, DriverVersion, 0) Then
                SendMessage(0, WM_CAP_SEQUENCE, 0, 0)
            End If
        End Sub

        Public Shared Sub StopRecording()
            SendMessage(0, WM_CAP_FILE_SAVEAS, 0, "C:\records\" & Now().ToString() & ".avi")
        End Sub
    End Class

Answer 1

I have found an answer. I am generally used to web development, and not so much windows forms development, and I realized that I can create a variable of type picture-box, and voila, I had a handle to reference.

For information, I have my code below, after I re-factored it a bit.

Const WM_CAP_START = &H400S
Const WS_CHILD = &H40000000
Const WS_VISIBLE = &H10000000

Const WM_CAP_DRIVER_CONNECT = WM_CAP_START + 10
Const WM_CAP_DRIVER_DISCONNECT = WM_CAP_START + 11
Const WM_CAP_EDIT_COPY = WM_CAP_START + 30
Const WM_CAP_SEQUENCE = WM_CAP_START + 62
Const WM_CAP_FILE_SAVEAS = WM_CAP_START + 23

Const WM_CAP_SET_SCALE = WM_CAP_START + 53
Const WM_CAP_SET_PREVIEWRATE = WM_CAP_START + 52
Const WM_CAP_SET_PREVIEW = WM_CAP_START + 50

Const SWP_NOMOVE = &H2S
Const SWP_NOSIZE = 1
Const SWP_NOZORDER = &H4S
Const HWND_BOTTOM = 1

Declare Function capGetDriverDescriptionA Lib "avicap32.dll" (ByVal wDriverIndex As Short, ByVal lpszName As String, ByVal cbName As Integer, ByVal lpszVer As String, ByVal cbVer As Integer) As Boolean

Declare Function capCreateCaptureWindowA Lib "avicap32.dll" (ByVal lpszWindowName As String, ByVal dwStyle As Integer, ByVal x As Integer, ByVal y As Integer, ByVal nWidth As Integer, ByVal nHeight As Short, ByVal hWnd As Integer, ByVal nID As Integer) As Integer

Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Integer, ByVal Msg As Integer, ByVal wParam As Integer, <MarshalAs(UnmanagedType.AsAny)> ByVal lParam As Object) As Integer

Declare Function SetWindowPos Lib "user32" Alias "SetWindowPos" (ByVal hwnd As Integer, ByVal hWndInsertAfter As Integer, ByVal x As Integer, ByVal y As Integer, ByVal cx As Integer, ByVal cy As Integer, ByVal wFlags As Integer) As Integer

Declare Function DestroyWindow Lib "user32" (ByVal hndw As Integer) As Boolean

Private hWnd As Integer
Private DriverVersion As Integer
Private mypicture As PictureBox = New PictureBox()

Public Sub New()
    DriverVersion = ReturnDriver()
    hWnd = capCreateCaptureWindowA(DriverVersion, WS_VISIBLE Or WS_CHILD, 0, 0, 0, 0, mypicture.Handle.ToInt32, 0)
End Sub

Private Function ReturnDriver() As Integer
    Dim DriverName As String = Space(100)
    Dim DriverVersion As String = Space(100)
    Dim DriverIndex As Integer = Nothing
    For i As Integer = 0 To 9
        If capGetDriverDescriptionA(i, DriverName, 80, DriverVersion, 80) Then
            DriverIndex = i
            Exit For
        End If
    Next
    Return DriverIndex
End Function

Public Sub StartRecording()
    If SendMessage(hWnd, WM_CAP_DRIVER_CONNECT, DriverVersion, 0) Then
        SendMessage(hWnd, WM_CAP_SEQUENCE, 0, 0)
    End If
End Sub

Public Sub StopRecording(byval FileName As String)
    Try
        FileName = "C:/records/_" & FileName & ".avi"
        SendMessage(hWnd, WM_CAP_FILE_SAVEAS, 0, FileName)
        SendMessage(hWnd, WM_CAP_DRIVER_DISCONNECT, DriverVersion, 0)
        System.IO.File.Delete("C:/CAPTURE.avi")
    Catch ex As Exception

    End Try
End Sub

No that I have the code running, I see that the videos cannot be compressed using avicap32.dll and it is saving 200 MB videos for 10 second captures. It seems like I'll have to make sense of DirectShow.net.

Answer 2

What you want very likely cannot be done. VFW and even some DS filters/players require an hWnd to draw the video output. Without it, there is no video output and therefore nothing to capture. You could try to trick it by drawing to a hidden or offscreen control, but then Windows just skips painting because it is offscreen. VFW just isnt very flexible.