The SDK provides special .ConversionTimeOut property to control the length of the video to convert (in milliseconds). So if you have infinitely looped SWF movie then you can set .ConversionTimeOut property to the required duration in milliseconds.
Imports BytescoutSWFToVideoLib
Module Module1
Sub Main()
' Create an instance of SWFToVideo ActiveX object
Dim converter As New SWFToVideo()
' Set debug log
'converter.SetLogFile("log.txt")
' Register SWFToVideo
converter.RegistrationName = "demo"
converter.RegistrationKey = "demo"
' Add SWF file and set its output filename
converter.SetMovie("HelloWorld.swf", "result.avi")
' This property is for one-frame or endless SWF movies.
' Will stop conversion after specified time (milliseconds).
converter.ConversionTimeOut = 5000 ' 5000ms = 5s
' Set output movie dimensions
converter.OutputWidth = 640
converter.OutputHeight = 480
' Run conversion
converter.RunAndWait()
' Open the result movie in default media player
Process.Start("result.avi")
End Sub
End Module