Option Explicit
Sub test()
MsgBox TC24ToFrames("01:23:45:19")
End Sub
'HH:MM:SS:FF
Function TC24ToFrames(TC As String) As Long
Dim v As Variant
v = Split(TC, ":")
TC24ToFrames = v(3) + (v(2) * 24) + (v(1) * 24 * 60) + (v(0) * 60 * 60 * 24)
End Function