CHROMECAST does NOTHING seems to be the short answer!
At least until you download SPECIAL APPS: Chrome Browser first of all, then you can "cast"
whatever you see in the browser to your TV (may be really laggy).
Then a special (new) version of YouTube app, then you can "cast" some YouTube content to your TV.
Apparently everything you want to "cast" requires it's own app!
Confirm or dispute, anyone? Thanks.
Further grousing: DLNA works badly, but is BUILT INTO (apparently?) both Gallery and the Video Player on my Samsung GS3.
But ChromeCast is built into NOTHING (although it comes from Google, who originated Android!)
(OK now it is built into Chrome Browser and Youtube App, and more apps as time goes by)
Apples and Oranges, I guess, DLNA came from some committee sort of organization I think.