Device not seeing certain files

Hi
New to Serviio and these forums.
I have no problems with my device (LG HB405SU Blu Ray Player) seeing serviio and the files. However it only shows .mkv format. It will not show mp4 or .avi.
I have Serviio installed on my desktop PC running Win7 Professional 64 bit.
Anyone have any ideas as to why?
Thanks
New to Serviio and these forums.
I have no problems with my device (LG HB405SU Blu Ray Player) seeing serviio and the files. However it only shows .mkv format. It will not show mp4 or .avi.
I have Serviio installed on my desktop PC running Win7 Professional 64 bit.
Anyone have any ideas as to why?
Thanks