On the Web, documents are identified using URLs, describing the transfer protocol, and often the server host and file location. When viewing a document, the browser identifies the document type either by examining parts of the URL, or, if the transfer protocol is HTTP, by looking at headers sent by the HTTP-server.
There are several ways to make a Web browser handle documents of which it has no built in knowledge, in our case video. The browser may start a helper application, an external program written to handle the video. For simple animations, server push, client pull or animated GIFs may be used.
Full integration of video may be achieved in several way, including the brute force method of rewriting the browser source code. Rewriting the source code makes it hard to incorporate several extensions from various developers. Plug-ins allow browser code extension without changing the code, using dynamically loaded libraries. Using plug-ins, developers may distribute platform dependent, precompiled extensions to several popular browser programs. Java applets are programs written in the Java language, interpreted by Java Virtual Machines in several of the major browsers. The main benefit of Java is portability, as Java programs are not compiled to machine code, but rather to Java byte code. Currently, Java has little built-in support for video, but the future will hopefully change this.