Videomaker – Learn video production and editing, camera reviews › Forums › Technique › Production Gear › Live Chromakey › If you don’t already have one
If you don't already have one you will need a software to make live streaming possible. I read good reviews about Wirecast (I use BoinxTV, Mac only). With that software you can attach hardware such as Blackmagic Intensity Shuttle with your S-video or composite cables. There are other cheaper alternatives such as an EasyCAP, but if you have the budget consider investing in Blackmagic products.