With Plex for Android, you can send any video from your device's 'camera roll' to your Chromecast, Android TV, Fire TV, Plex Home Theater, and even Xbox One and Playstation 4 (after prior installation of their respective official apps). In addition, you can control the videos directly from the screen of the device as if it were a remote control.
It's important to note that even though Plex for Android is a free app, this version only lets you play a minute of video or audio. To be able to watch longer multimedia files, you have to unlock the full version. The good thing about this is that it gives you the chance to decide whether or not it's worth it.
Plex for Android is a video, audio, and picture streaming app that you can use to send all your multimedia content to other devices with bigger screens.