Movie Quality using Plex on Roku

I have successfully set up My Cloud Home with Plex and ripped some movies in MP4 format. Watching through Plex on my iphone or ipad is great, but through Roku (on more than one TV) the quality isnt as good. The audio is fine but the video is choppy. I’m using WinX DVD Ripper on an iMac.

Any ideas what i can do?