Bplex has hit it on the head. I use to run a torrent tracker site www.torrentstorage.com and found myself getting multiple dmca emails everyday. Torrent technology is a Grey area since the actual content is not hosted on the server. All you provide is a hash that allows users to connect to each other to share this content. Video hosting is the opposite. The content is actually on the server meaning it would make a easy way to prosecute you .
You must agree with the dmca and remove copyrighted content as its requested in a timely manner. keep in mind that it cost a lot on money for the owner to actually take you to court meaning a bulk of the threats are shallow .
keep in mind that all countries have different laws that don't apply everywhere. you need to know what laws apply to the country your server is located at. Until your site becomes a house hold name like youporn rebtube or so on you will stay under the radar. Most of these company can care less about a site that only get s a few hundred hits a day. They may make threats, but the reality of the situation is its not worth their time to fuck with you .
So its as easy as sticking to homemade videos and buying the rights to professional videos.
I must also tell you if you dont have a fat bank account or a shit load of time than you better consider trying to market something other than porn. The industry is cut throat and without 100 percent of your dedication you site will vanish just as fast as it arrived in your brain.
I currently make 600 - 1000 a month at www.monitorporn.com
You must be prepared to invest a 100 percent of that back or your not going to go anywhere.
Regards