Pictures and Music are displayed fine but not mkv files

Hello there!
I am new here at Serviio and I have encountered a problem that seems rather strange. I have a SAMSUNG ue40d8000 (D8000 series) and while its IP is displayed to my laptop, the name of the TV is not (unrecognized device). Furthermore and more important, in the TV's menu the pictures and music are displayed perfectly (accessed as well), but my movies, which are all .mkv files, are not. In detail, thumbnails of the movies are displayed, but when I am trying to access the file, I get a ''not supported file format''.
Can somebody help me with this, with simple steps, as I am not familiarised with transcoding, etc.?
Thanks in advance!
I am new here at Serviio and I have encountered a problem that seems rather strange. I have a SAMSUNG ue40d8000 (D8000 series) and while its IP is displayed to my laptop, the name of the TV is not (unrecognized device). Furthermore and more important, in the TV's menu the pictures and music are displayed perfectly (accessed as well), but my movies, which are all .mkv files, are not. In detail, thumbnails of the movies are displayed, but when I am trying to access the file, I get a ''not supported file format''.
Can somebody help me with this, with simple steps, as I am not familiarised with transcoding, etc.?
Thanks in advance!