I strongly recommend using something other than the built in DLNA server that comes in Windows. It does very little transcoding of the media can't be played by your Roku. The two I recommend the most is Serviio and Plex. Serviio has great support and is vastly customizable, while Plex offers a great user app for the Roku. Of course, RMP works with Plex as well if you enable DLNA in the Plex server settings.
Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.