@jhalewood You can use JPEG/MJPEG, which is what Motion webcam server provides (see DSF in the linked article). Basically you can use any format that can be displayed in a browser; if it cannot be rendered using an img tag, you can still embed the remote stream using an iframe.
AFAIK only MJPEG is generally supported in browsers. If rtsp was supported, I'd add support for it, too.