Question

是否有一种简单的方法可以让DirectShow检测网络摄像头是否已插入（USB），或者有人拔掉它（然后轮询或搜索）？

我见过Microsoft Media Foundation的代码，但它很复杂，并且Media Foundation不能安装在＆lt; Vista，afaik。

Thx，WW

Answer 1

我使用WMI事件观察器在属性字符串中查找PID（某些摄像机可能会根据驱动程序触发事件两次）。这是一个VB.Net示例：

 Dim CamEventWatcher As ManagementEventWatcher
 Public Delegate Sub SetMessageCallback(ByVal [_Msg] As Boolean)

Private Sub MessageCallback(ByVal _Msg As Boolean)
    If (_Msg) Then
        'cam connected
    Else
        'camera removed
    End If
End Sub

Private Sub RemoveCameraUSBHandler()
    Try
        If Not CamEventWatcher Is Nothing Then
            CamEventWatcher.Stop()
        End If
    Catch ex As Exception

    End Try
End Sub

Private Sub AddCameraUSBHandler()
    Dim q As WqlEventQuery

    Dim scope As ManagementScope = New ManagementScope("root\CIMV2")

    scope.Options.EnablePrivileges = True

    Try

        q = New WqlEventQuery()

        q.EventClassName = "__InstanceOperationEvent"

        q.WithinInterval = New TimeSpan(0, 0, 1)

        q.Condition = "TargetInstance ISA 'Win32_USBControllerdevice'"

        CamEventWatcher = New ManagementEventWatcher(scope, q)

        AddHandler CamEventWatcher.EventArrived, AddressOf CamUSBEvent

        CamEventWatcher.Start()
    Catch ex As Exception
    End Try
End Sub

Private iCreatedFired As Integer = 0
Private iRemovedFired As Integer = 0
Public Sub CamUSBEvent(ByVal sender As System.Object, ByVal e As EventArrivedEventArgs)
    If e.NewEvent.ClassPath.ClassName = "__InstanceCreationEvent" Then

        Dim sAntecedent As String
        Dim sDependent As String

        sAntecedent = e.NewEvent.Properties("TargetInstance").Value.Properties("Antecedent").Value.ToString() + ControlChars.CrLf

        sDependent = e.NewEvent.Properties("TargetInstance").Value.Properties("Dependent").Value.ToString() + ControlChars.CrLf

        If sDependent.Contains(CAM_DEV_ID) Then
            iCreatedFired += 1
            If (iCreatedFired = 1) Then
                e.NewEvent.Dispose()
                Return
            End If
            iCreatedFired = 0
            iRemovedFired = 0
            Dim _delegate As New SetMessageCallback(AddressOf MessageCallback)
            Me.Invoke(_delegate, New Object() {True})

        End If
    ElseIf e.NewEvent.ClassPath.ClassName = "__InstanceDeletionEvent" Then

        Dim sAntecedent As String
        Dim sDependent As String

        sAntecedent = e.NewEvent.Properties("TargetInstance").Value.Properties("Antecedent").Value.ToString() + ControlChars.CrLf

        sDependent = e.NewEvent.Properties("TargetInstance").Value.Properties("Dependent").Value.ToString() + ControlChars.CrLf

        If sDependent.Contains(CAM_DEV_ID) Then
            iRemovedFired += 1
            If (iRemovedFired = 1) Then
                e.NewEvent.Dispose()
                Return
            End If
            iCreatedFired = 0
            iRemovedFired = 0
            Dim _delegate As New SetMessageCallback(AddressOf MessageCallback)
            Me.Invoke(_delegate, New Object() {False})
        End If
    End If

    e.NewEvent.Dispose()
End Sub

directshow - 如何检测网络摄像头插头/拔出？

1 个答案: