How many times is video transferring using Chromecast?

Question

Setup: My home setup is quite simple. I have a Sky Router which provides wireless and wired contectivity to around a dozen devices. Two of those are Chromecast dongles that plug into our TVs.

Question: When using an iPad (or similar) to 'cast to a chromecast how many times is the video stream bouncing around my home? E.g. I can see two likely scenarios

1) The stream is sent from the internet, to my router, to my ipad then from my ipad to my Chromecast. Thus the stream is travelling twice on my home network and thus doubling the amount of local network usage (right?) as opposed to watching it locally on the iPad

2) the Chromecast software sets up the Chromecast to receive the video stream directly using magical Google elves, i.e. the stream comes from the internet, to my router to my Chromecast

Which of these is true (or close enough) or is there a 3rd option?

Answer 1

Only once.

The application on your ipad provides the chromecast with a specially formed URL to load the stream from - this can include other details, which app it's coming from, where about's in the stream to start etc.

Once it's loaded on the chromecast, no more 'streaming' data is going via your iPad - infact you can test this simply by turning your ipad off once you've loaded the stream on the chromecast.

Obviously if you're streaming something you're doing interactively on your iPad, this isn't the case - such as if your casting your browser activity, rather than simply casting the video.