My wifes first shots were done afocal with a cannon powershot 495 by hand, with a dob and no tracking. This method produced some unreal images of Saturn and Jupiter using registax, most of them are better then the ones done with the celestron nextimager
You can always convert then video to a format that registax supports if need be, so no it doesn't have to be .avi. The main thing is the codec used and using the least compression possible to give registax the best quality data to work with. A big tip to make life better is to make or buy a bracket to hold your camera steady, and dont use digi zoom only optical. Here a useful link
http://www.astronomyforbeginners.com...phy/afocal.php