[Help] is it possible to change startup videos?

Ok. So my reasons to change them is that, I'm basically making a stupid meme texture pack type of thing in the game that I'm only doing for me and my friends since it includes a lot of injokes. And including that I want to change the startup videos to basically sorta troll them in the boot up of the game. So I took the video I wanted, put it in Sony Vegas, exported it as an avi with the same name as the original. Replaced the original (I did keep the original in a separate folder. Well. I have all the textures and sounds in a backup just in case), opened the game, and i could hear the audio of the one I put, but it did not show the video. I only replaced the startup_Undertow.avi since I was testing if it would work. And when the audio ended it showed the startup_TTS.avi fine. Do I need any specifications as how I export it? Please Its something I really want to do to show my friends and have some fun.