What is Chromecast built-in and how can I use it?

Chromecast built-in - formerly Google Cast - is a technology that allows you to stream music directly from your smartphone to selected Wi-Fi speakers via music apps without any prior knowledge or technical effort. By tapping the corresponding streaming icon on supported apps, a sound system such as MOTIV® GO VOICE can be selected as a player.

More info is available here: Streaming with Chromecast built-in