Problem when checking for valid filetype

[Chris001]

Hello, I'm using the code below to check how many valid avi videos there are in a folder.

Every time a valid avi video has been found, 1 should be counted up (ct). This works fine if there are only valid avi videos in the folder, but if I rename a mp3 audio file to .avi and put that file in the folder with the valid avi videos, then ct always returns "0".

Does anybody know what is wrong?

Public Function GetFileType(xFile As String) As String
    On Error Resume Next
    Dim ID As String * 300
 
    Open xFile For Binary Access Read As #1
    Get #1, 1, ID
    Close #1
    GetFileType = Mid(ID, 9, 8)
End Function
 
 
 
Private Sub cmdCheck_Click()
  Dim ct As Integer
  Dim a As String
  Dim Valid_type As String
 
  ct = 0
  a = sPath & Dir(sPath & "*.avi")
  Valid_type = GetFileType(a)
  
  Do While LenB(a) > LenB(sPath)
    
    If Valid_type = "AVI LIST" Then
    ct = ct + 1
    End If
    
    a = sPath & Dir
  Loop
 
Msgbox ct
 
End Sub