Unfortunately, there is no way to add additional codec support to any Roku. Your only options are to either re-encode your videos using H.264 or H.265, or use a DLNA server to transcode and stream the videos to your player. I do the latter, using Serviio as my DLNA server. There's also Plex, which can act as a DLNA server or use its native Roku app. And there are many other possible choices that support all the usual operating systems.
The disadvantage of running a DLNA server is the need to keep a separate computer (or NAS) running on your network. However, it has a major advantage in that you can now stream your media to any device on your network, and support more than one stream at a time, depending on your server hardware's capabilities. Since I leave all of my computers on 24/7 anyway, there's no down side for my operation.
Nvidia Shield, Roku Stick (2016), and Ultra (2016), Insignia Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network. Samsung JU7100 4K TV, Yamaha RX-V583, CenturyLink DSL