You're hung up on mp4 vs wmv and you're wasting your time.
Those are container types - what matters are the streams codecs.
I attempted a write up for Chromecast on that subject here -
http://androidforums.com/index.php?posts/6323266
Saying that you have an mp4 is like saying that you're trying to ask out Smith - without saying if you mean Anna Bella Smith, Carly Mae Smith, or James Frederick Smith.
Converting to a wmv is like saying, if I change their last name to Jones do you know who I mean now?
What codecs are you trying to play?
X264 in the title suggests that it ought to contain an H.264 video codec stream - probably a good idea to be sure that you haven't converted your disks using 10-bit video.
The audio codec is equally important.
And avoid wmv files wherever possible - that's a vendor-specific container (always a bad idea) and it's Microsoft's idea on how to handle media (impossible to do worse and that's not an opinion or blind Microsoft hate). Stick with mp4 wherever possible.
You've also mentioned that the files are big?
What does that mean in numbers?