do i need the chromecast app to cast
The following is a partial list of apps compatible with Google Cast, and the platforms on which each can run. The first Google Cast receiver released was Google's Chromecast in July 2013; a digital media player in the form of an HDMI dongle, the device streams media wirelessly via Wi-Fi after a selection is made through a supported mobile or web app, such as those listed below. Unofficial Google Cast receivers followed, before Google released a second official receiver, the Nexus Player, in November 2014.
List of apps with Google Cast support