UserAgent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36

Steps to reproduce the problem:
Try to capture/record (share) the screen (the whole or application/window/tab only).

What is the expected behavior?

What went wrong?
As of today, screen capturing/recording (sharing) in Chrome is available via {"mandatory": {"chromeMediaSource": "screen"}} video constraint. But:

1. it's only for Android
2. it requires enabling chrome://flags#enable-usermedia-screen-capturing flag
3. "mandatory" is old constraint syntax
4. "chromeMediaSource" is non-standard, Chrome-only thing

Also Chrome has tab sharing implemented via {"mandatory": {"chromeMediaSource": "tab"}} video constraint, but it works only in Chrome extensions.

There is a W3C MediaCapture Screen Share API spec (https://w3c.github.io/mediacapture-screen-share/). What about implementing it for all platforms (desktop and mobile)?

Currently, Firefox has partially implemented W3C MediaCapture Screen Share API spec on all platforms (mobile and desktop, not only Android) without any flags:

* {"mediaSource": "window"} video constraint to capture only application window
* {"mediaSource": "application"} video constraint to capture all application windows

Some caveats:

* Firefox uses non-standard {"mediaSource": "screen"} video constraint instead of {"mediaSource": "monitor"} to capture the whole screen
* Currently, Firefox doesn't support {"mediaSource": "browser"} video constraint

Firefox (before version 52) requires to set media.getusermedia.screensharing.enabled to true and add the web app domain to media.getusermedia.screensharing.allowed_domains in about:config.

BTW, Chrome doesn't support combining screen capture video tracks with audio tracks.

In Firefox it's easy to create a stream that contains both audio and video tracks as well. Any combination of devices and constraints can be used when configuring.

Did this work before? No 

Does this work in other browsers? Yes

Chrome version:   Channel: canary
OS Version: 
Flash Version: 

This issue is for all platforms (desktop and mobile).