Q:

Does the Google Cast extension for Google Chrome support 1080p?

In the Options for the Google Cast extension under 'Tab projection quality', there are three options:
Extreme (720p high bitrate)
 High (720p)
 Standard (480p)
1080p is not listed.
I assume if I play a 1080p video that it will work because it's sending the video url to Chromecast, but am I limited to 720p for regular HTML webpages?

A:

This appears to be more of a user question, not a development question.
The Google Cast extension for Chrome provides two major functions:

Chrome Mirroring - which is limited to 720p - This acts by encoding your tab to WebM/Opus and then sending to the Chromecast device.
The Google Cast API for Chrome which allows your webpage to cast a video to a Chromecast device.  Which, of course can be full 1080p.  Official documentation.

