Plugin options metatitle and metasubtitle are optional, allow to display media title and subtitle on both, player container and chromecast receiver. If you prefer Chromecast button in control bar (right from fulscreen button) than a bigger button in the top-left corner of the player you can use another Chromecast plugin option button:'controlbar'.
If you want to enable subtitle Tracks for any media, you must enable CORS for both your track streams and your media streams. If you do not have CORS headers available even for your simple mp4 media on your server, and you then add a simple subtitle track, you will not be able to stream your media unless you update your server to include the appropriate CORS headers. Read more on https://developers.google.com/cast/docs/... You may also need to set crossorigin attribute for video tag, e.g. crossorigin="anonymous".