Just so you know, if you are considering buying a Roku, Android USB Stick or WD Live box to watch .mkv or .flv files, DON'T! Vizio TV's Can Play Matroska and Flash (.mkv and .flv) Video Formats!
I now love my Vizio 70" TV even more... Yeap, besides .asf, .wmv, .avi (Xvid & Divx), .mp4, .mov, .mpg, .mpeg, .vob (DVD), and others that it can see from a USB device, you can change the file extension for .mkv and .flv to .mp4
and you will be able to see the file on the Vizio Media app, just click on it and it will load the correct codecs for the file and play it beautifully.
Note: .webm, and .rmvb won't play due to missing codecs (.RMVB will only show a black screnn with audio since it loads the .rm or .ra audio codecs).
My guess is that the processor they are using like the Armada on the Co-Star, can play many formats but due to licensing they do not enable all of them and only let you see some of them. Since the codecs are there, it by default loads the correct one to play the container even if it has another file extension just like VLC Player and others due.
Much better than a Roku (can only play .mp4 and some .mkv types) and no need to transcode or buy an Android box or WD live box