If you come across an embedded video online that isn't piped in from YouTube, odds are pretty good that it's running on JW Player. The HTML5 and Flash video player from this company is used on more than 2 million websites including Kickstarter, Electronic Arts, and ESPN. That's why it's kind of a big deal that JW Player is adding support for Chromecast.
Just like when watching a YouTube video, JW Player will have a Chromecast button that can be used to beam the video to your TV. The Chromecast implementation from JW Player could also enable multiscreen experiences where a casted video is accompanied by clickable information or sharing controls on the second screen device.
This isn't going to happen overnight, unfortunately. The company is planning to add support to a few big partners as a beta run, then expand support later.