I want to create a website, a chat where people could discuss in real time. I also want them to exhange pictures, sounds, videos and have webcam. I want this for thousand (in the long term) of people at the same time. What is the best architecture for that ? just javascript, ajax, php and MySql ? Should I prefer Java and a war deployed on a Tomcat ? And what about GWT ? And what about websocket ?

I have no idea what to use there are so many web technologies, thanks in advance to advice me what to choose.

Jean Savant