a ".ahf" file is not a video format. It's really a file that just tells the AH Film Viewer program what happened, where at etc. and then the Film Viewer program generates game footage from that.
What you need to do is download a program like Fraps (
www.fraps.com) and record what you're watching on the film viewer. What Fraps records will be in an AVI video file. Note: Fraps recordings are lightly compressed so 30 seconds of film can be hundres of megabytes. You'd need to compress the footage with another program.
Otherwise, you can output AVI video files through the AH Film Viewer as well. Just click the Save As AVI button on the top right hand of the film viewer. This is the easiest way to get video files.