I don't think that's because of Plex but just because the Chromecast wants one when you first start it up? I haven't had mine plugged in for a while but the first thing it does is demand a connection to a WLAN.
Here's my situation. I am going up north for a week with a bunch of kids and staying at a house that does not have internet access. I have all my streaming content/movies on a laptop (about 250GB) for them to watch when they want. Plex is installed on the laptop. My plan is to bring a wireless router with me so that the laptop and the Chromecast can talk to each other through it and stream content to a TV with the Chromecast. The fact that Chromecast requires an internet connection throws a monkey wrench into it.
Glimmer of hope: My phone has the mobile hotspot feature enabled so I can get internet access through it.
However, how do I get the laptop and the Chromecast to talk to each other while the Chromecast is also connected to the internet via the mobile hotspot? As far as I know, the phone cannot act as a wireless router. If it could do that I think the problem would be solved.
Would allowing the laptop to connect to the mobile hotspot and then somehow sharing that connection (essentially turning the laptop into a router) with the Chromecast work? In that situation would the Laptop be able to stream to the Chromecast?
Never mind. I'm confused. You'd need the laptop on the same WLAN as the Chromecast for that to work. So everything would have to run through your phone. Which would probably run about two hours unless it was plugged in to AC power. You'd be better off just plugging you laptop straight in to an HDMI port on the TV or whatever.
Aw hell, probably the easiest thing to do would be take my work laptop ,throw my old SSD into it , and install Windows 7. It has HDMI out. I guess I could play right from the laptop that way. Is there any software that I could use to control it remotely with my tablet or something ? I'll have to do some experimenting but would appreciate any advice you can provide.
I'm sure the kids would like to watch a movie at night sometimes. We'll be out on the beach/lake all day for the week. Anyway...I thought the laptop had HDMI out but it doesn't. BOO! I guess if they want to watch they can watch on the laptop! I will bring my router just on the odd chance that the house we're renting has internet access.