Okay, tank you for your answers :) And sorry for the slow reaction...

I have this Samsung blu ray player and it support mkv files:

http://www.samsung.com/us/support/owners/product/BD-D6500/ZA

And I have a NAS and when I want to play mkv files from it to the player, the player says: This format isn't supported! (Mkv), but it play the MP4 format from it... when I play the mkv file from usb, it play it.

Have anyone any idea?

Thank you!