It is possible to watch video playback in full-screen, right click anywhere in AKtion and choose "Full Screen", to exit, left or right click on the screen. You may need to enable this feature if it does not currently work.
If possible, use the XFree86 VidMode and DGA extensions. These extensions allow the application to automatically change the screen resolution to better fit the size of the video. Traditionally a video, of say, 320x200 would be scaled up on a 800x600 display. This scaling requires extra work and the result is not appealing at all. In the setup dialog there are two check boxes of interest
enable full screen mode
AKtion takes control of the mouse in full screen mode