I'd like to examine the possibility of writing an unofficial Windows 8 (WinRT/Metro) sender API for Chromecast. The goal would be to allow Windows 8 Store apps roughly the same functionality of iOS / Android apps through the official sender API available for those platforms.
I've noticed that, although the inner workings of the API haven't really been exposed yet, some of the source code for the Chromecast device is available, and there's an unofficial emulator for the device out on Github (https://github.com/dz0ny/leapcast).
Is this possible, given how Chromecast devices seem to take commands directly from Google?
ChromeCast is using a proprietary protocol called RAMP (Remote Application Media Protocol) to do media control. Once you have setup your ChromeCast device for development, the device will open a port for remote Chrome debugging. Open Chrome at your ChromeCast device IP address port 9222: http://192.168.0.x:9222/
You should see a page with a link to the receiver page of the currently running ChromeCast app. Click the link and then use Chrome developer tools on that page. Take a look at the network and console tabs to see the RAMP commands.
I have open sourced an Android app that shows you how to discover ChromeCast devices and setup the Websocket connection to handle the RAMP commands: https://github.com/entertailion/DIAL