Do I need to develop Android TV Receiver App to cast from existing sender app to "Chromecast with google tv" device?
I thought just web receiver app would be okay for casting without registered android TV app just like Chromecast.
You do not need to developer an Android TV receiver app to cast to the Chromecast with Google TV. A standard web receiver will work on this device the same as a typical device running the Android TV OS. The main reason to use the Cast Connect library to build an Android TV receiver app is if you already have an Android TV app and want to give a more robust casting experience (e.g., allowing users to control playback with their remote control or providing a UX that's easier with native Android code).