I don't use Chromecast but after some Google Fu it's apparent that native RTSP streams from most IP cams cannot be streamed directly to Chromecast. I believe only Google's "Nest" cams are readily streamed to it with not much fuss.
The RTSP stream from the
Uniview must be converted first to HLS format using a PC / laptop or Raspberry Pi and third party software.
The most popular third party software for such conversion is VLC. There will be some delay on the live stream, maybe as little a 5 seconds but possibly as much as 30 depending on the complexity of the RTSP stream (camera resolution, bitrate, etc.) and the processing ability of the PC or laptop when using VLC to render the compatible stream that Chromecast wants.
So if it sounds like you're up to it, find the URL for your cam's RTSP stream, get your PC or Pi ready, install VLC and jump in. Here's a fairly good guide with a video and I'm sure there are many more, maybe some better. ==>>
How to stream video from security camera to Chromecast