The Chromecast conceptual model

Google makes a device called Chromecast. It's a relatively inexpensive way to turn any TV into a "Smart" TV capable of playing movies or music. It's a clever bit of engineering, but I've run into a few people who have trouble understanding how they work.

The key thing to understand is that the Chromecast is the device that's actually receiving and playing the movie (or whatever), and your phone is just the remote.

Here's how the process works at a high level:

1. You start watching a video on Youtube
2. 30 seconds in, you decide that you'd like to watch the rest on your TV, so you press the "Cast" button.
3. Your phone stops playing and tells the Chromecast "Get this video directly from Youtube and start playing at the 0:30 mark" 
4. When your phone initially asks the Chromecast to start playing, it also specifies a "default thing" to do when the Chromecast is finished. If the Chromecast is playing a Youtube video, it might automatically start playing another video. If it's playing a movie, it might switch to movie trailers when it's finished.
5. The Chromecast starts playing the video and announces that fact over the network.
6. From the Chromecast's perspective, your phone is no longer needed. Any phones on the network who see the "Now playing" message can control the Chromecast, but none HAVE TO control it. You can turn off your phone, leave the house and make a call, etc. without affecting what's playing.
7. To make the Chromecast stop, another device on the network (your phone, someone else's computer, etc.) must ask it to stop.
8. There can be problems when a phone makes assumptions about what the Chromecast is doing. For example, if there's a problem with a video and the Chromecast decides to stop or go to another video, your phone might not notice the change. So your phone says, "Playing your favorite song" while the Chromecast is actually playing "10-hour Nonstop Nyan Cat". Usually, pressing stop and play a few times on your phone will bring everything back into sync. The important thing to remember here is that it's the app on your phone that's confused, not the Chromecast. So, if the app won't stop the Chromecast, try another app (the Google Home app is often a good choice) or another phone.

I hope that this is helpful the next time you're trying to use a Chromecast.