If you have a Safari Books Online, the Safari To Go app for Android is useful for reading the books (particularly offline) and watching the videos, but when you watch the videos there is no option to send it to Chromecast. It would be nice to watch the videos, which include training videos and popular conference sessions, on my TV using Chromecast.
Instead of using the Safari To Go app, go to http://m.safaribooksonline.com and log into your account there. When you start playing the video, maximize it and the Chromecast icon will appear in the upper left. Tap that icon, select your Chromecast device, and the video will appear there. As always, you can use your Android to control volume, pause/play, and seek within the video.