video converter
 

please introduce me a cross-platform video converter with ability of converting wmv to vcd(DAT)

You can try Avidemux2 (I Think it takes wmv).

I don't think it does do wmv, i use it a bit and i think wmv's the only major file type it doesn't support. I think you need mencoder, that'll do all the file types and convert anything you want but i personally find the command line a bit of a bugger. There are a few gui's about though if you google them, nothing i'd really recommend exept maybe acidrip and i'm not certain that that does wmv's either.

I just checked Avidemux V2.3 handles wmv (at least the ones I tried).

Cool, i've found wmv's a nightmare so far but it seems that there's only version 1.something available on the ubuntu software channell so i got the newer one off the website.