Awesome new app for chromecast: Wondershare DreamStream. FREE CODE for next few hours
I say "awesome" because this is the first clean solution to playing avi videos on the chromecast. Needless to say, it supports most of the other common file types too. Working flawlessly here on Windows 8.1 Update 1. It also does away with the need for the chrome browser for streaming local videos.
They are giving away free codes for the next few hours, so get it while you can.