im not 100% if ps3 plays mkv's but i heard they do. but the movie must be under 4gb. ps3 only reads fat32 and you cant put anything over 4gb on a fat32 usb.

but if its a mkv i think i know where you got it from so use vuze and you might able to play it through vuze and get it to play on your ps3. but like i said, im not 100% but do a little bit more research about playing it through vuze and i think that should work

No the ps3 doesn't have mkv support... Only way to play an mkv file is through streaming it from your computer or have a jailbroken ps3 with showtime.