Google Chromecast owners will soon be able to cast a file natively from their device's local storage via a "Cast File" option, currently available in select builds of Chrome in beta form. The feature can only be enabled via a flag for the time being. Rather than delving into the Chrome://flags menu, you'll have to use command line flags when booting up Chrome. The new feature presents a simple "Cast File" option in the Cast menu, which allows users to pick a piece of local media like a video file, audio file, or picture, then send it out to any Chromecast-enabled display.
The new feature does not bring support for any additional file formats. Many file formats are supported by default, but some common formats for older files like DIVX and 3GP are not on board. That said, simply choose a compatible file in the file picker that pops up when clicking on "Cast File", and it will automatically go into fullscreen mode on the chosen player. In order to run the experimental feature on Windows, you'll need to right-click on your Chrome or Chromium shortcut, click on "Properties", then add the text "--enable-features=EnableCastLocalMedia", without the quotes, into the target line of the shortcut. On Mac OS, you'll need to use the command line to run Chrome, then add in that flag text as a post-argument. Linux users, meanwhile, can simply pop open the console and type in "chromium-browser" or "chrome" and then the flag text. Depending on how your distro of choice handles privilege escalation, sudo may or may not be required. Generally, this will only be the case if your OS typically sandboxes internet apps, as seen in some versions of Puppy Linux.
This fairly basic feature has, up until now, required third-party apps or plugins. With the functionality intact, you'll be able to cast local files straight from Chrome without having to download or install anything first, and it should work with any Chromecast-enabled device, including TVs and speakers. For the time being, the feature is not present on Android, but it's not entirely unfeasible and may well come to the mobile sphere in due time.