This year I will be (trying!) to use Core Media Player for the category playlists.
I will also have one if not two back-up machines with VLC player on those.
In either case, when running maximized, these players fit to the available aspect ratio of the projector in the hall.
So, if we end up with an HD capable projector and you throw an older-style 720:480 AMV on it, it will show as centered within a black field.
Similarly, if we get an old, boat-anchor 640:480 projector and you throw 1:1.85 at it then the player should automatically letterbox it.
We all hope ...
But there are no restrictions on aspect ratios in the contest.
Each entry is individually play tested and confirm notices are sent privately to the creators.
These notices only report whether the playback was successful or not.
If not, I only state things like "Sound dropped out at 2min 38 sec" or other possible playback glitches.
I do not remark on the entertainment value of the AMV, i.e, "the story seemed to bog down around 2min 38sec."