I'll throw my 2 cents in and plug Emit. It lets you stream movies/music from your computer to your phone via Wifi and 3G/4G. Automatically transcodes, 2 minute setup time and support for Linux/OSX/Windows.
Free version is ad supported but works fine.
Edit - You can also pre-encode and download videos to your phone for when you're offline. I don't use this very often, but some people might be interested in it. There are faster ways but my gf likes it because it's a simple solution.
I'm not sure if you're specifically trying to avoid installing further software, but Emit is a decent video streamer. I use it on my Nexuses and, while it's not mind-blowing (would it kill one of these apps to have a playlist function?), it does the job.
Edit: I tried Emit (http://www.emitapp.com) as suggested by someone else in this thread. I think I'm going to switch to it because of the slicker interface and ability to share mapped network drives. You can also set a preset bitrate for when you're on 3G.
Subsonic does on-the-fly conversion, so if you're out of the house on 3G and don't want to stream a high quality video, it will downconvert the quality to 200k or 500k or whatever you want, so it can use your crappy mobile bandwidth. It basically loads up a flash video in a browser window and you can full screen it. It's weird, but it works!
It's kindof a pain to set up, but it's nice once it's going!
Also, I did have some minor issues sharing network drives. You can't do mapped drives. You have to have the direct network path (//steve/files/video/)
Also, you should know some things about port forwarding on your router(s) before you attempt to set up mobile or WAN access to your videos.
For LAN streaming on the same wifi as your server, you can just use ES File Explorer and a video player (I use MX Video Player) like that other guy suggested.
The question is why does it get detected as a virus and what are you going to do to mitigate that?
Edit: Here is the website for those that want to get the server for the PC.