If Offline Explorer Enterprise is too expensive for you,

and you can't find any alternative with google,

then IMHO the best way to find software or components (like ActiveX and DLL) is
by contacting the developers of streaming media recorders supporting rtsp:// .ASF video streams.


You can also create a project at a freelance marketplace and find a skilled programmer that can develop a custom ActiveX, DLL,... supporting rtsp:// .asf recording.