Well I’m late but for the next person who has the same query inorder to add Animated gifs to WP Headers you simply have to make sure the gif dimensions are smaller than or equal to whatever your header’s dimensions are. We have a video playlist header that I erroneously thought was 685×483 and have been making static images at that size for a year and always wondering why parts of them were always being cut off. Since I didn’t design the site I assumed that’s just the way it was with pics in the header. But after wanting to put an animated gif up and some research I came across the “gif will play if it’s smaller than the header window, but not if it’s bigger” solution. I’ve discovered my Header video window is 630×344 with my monitor set at 1680×1050 60Hz. You can see it here BCOMMTV.com
