I just bought a 1520 a few days ago from a Microsoft store for the $99 contract version. I copied a xvid and a divx movie directly over to my phone one on into the phone memory and the other on a SD card file explorer warned me that it might not play do you want to transcode it and it did both play fine and I have some .mkv files on it also all play fine not sure if it is a function of the codecs I installed on my laptop or not but can try it with a fresh computer to see. If I copy files over with the windows metro what do you want to do with this device wizard it does not give me the option to transcode
ThinkPad x230T running windows 8 enterprise 64bit and an ATT lumia 1520 RM-940 running nokia black update
To get moliplayer to see your copied files, you need to use the normal windows explorer view (not the app) and copy your files in the pictures/camera roll folder of the phone.
It will alert you saying you might not be able to play the files, but just ok it and go ahead! There has not been a file type moliplayer has not been able to play for me.