A couple of tips for Roku users:
The Android apps Avia and AllCast now support casting to Roku as well as Chromecast (Avia just recently, AllCast for a long time - but they just fixed a bug that broke it with the Roku firmware version 6 update a while ago). Not only can they play local content from the Android device or a network server, many Android apps that stream web video allow you to select "Other" as the video player instead of using a built-in video player. That allows you to open the streaming video link in Avia or AllCast and cast it to the Roku. Avia requires you to install their Roku app, while AllCast uses a built-in function in the Roku firmware. Either way, it works very well. Both apps have a free version, but there's a small fee to unlock the full capability. Plex has always supported casting to Roku, but they don't offer the ability to cast web streams from other Android apps.
PlayOn allows you to stream web video that you can play in a browser window on your PC to your Roku. It uses a PlayOn server on your PC to relay the video to the Roku. They offer standard channels for all the U.S. network video-on-demand sites (CBS, NBC, ABC, CW etc) and free Hulu, plus many others. For sites not directly supported, they offer a PlayMark browser extension that can grab and bookmark the streaming url of video playing in your browser window. It works more effectively than other such tools. They also offer real-time recording of any of the channels they can stream. But there's a subscription cost: monthly, yearly, or lifetime.