Screen casting means to put the screen image on other display devices.
For example, if you're watching a video on your cell phone and want to watch it on your TV, you can do that through the casting function.
However, the conditions for screen casting also need to be there, for example, Huawei P40 cell phone wireless screen casting function requires the big screen device to support the Miracast protocol, and the big screen device that does not support the Miracast protocol needs to be connected to the cell phone and the big screen device by the screen casting device. Screen casting via wireless WLAN LAN (WIFI) or wired HDMI interface.
Some TVs don't support direct casting, although there are many video APPs that support connecting through video box communication, connecting to the TV through the HDMI interface, and then the phone communicates with the video box through the wireless WLAN (WIFI) to ultimately realize the casting.