Ok, I see it now, they have updated it.
Some month's ago it did not work with mpg's, now it does. :)
Sorry, just tried it out on some mpg.
Gspots Says: type video/mpeg, all other info N.A.
Avicodec says: 1150kbps 29.970 FPS Res 352x240 4:3 Vcd
224kbps 2 channel, Mpg1 layer 2
So Gspost is not very usefull (newest version)