How do media browser plugins function?

If I want to use Google Video chat on my browser I have to download and install a plugin for it to work.

I would like to make a piece of software that creates

some interactions with a video displayed in the browser.

I assume that it might be problematic doing it with one solution for all the browser, so if I might need to focus on only one browser lets talk about firefox, although I think the firefox addon SDK would not let me do 开发者_如何学JAVAa thing as complex as video interaction.

But how does the Google Video chat plugin work for the browsers? It's only an example for one of those plugins that lets you do activities (media in this case) with your browser which are normally impossible.

As I understand it, Google Video Chat uses Flash.

I'm looking for something official-looking to back that up now...

Edit: I think this explains it pretty well.

Flash Player exposes certain audio/video functions to the (SWF) application. But the Flash Player does not give access to the raw real-time audio/video data to the application. There are some ActionScript API classes and methods: the Camera class allows you to capture video from your camera, the Microphone class allows you to capture audio from your microphone, the NetConnection/NetStream classes allow you to stream the video from Flash Player to remote server and vice-versa, the Video class allows you to render video either captured by Camera or received on NetStream. Given these, to display the video in Flash Player the video must be either captured by Camera object or received from remote server on NetStream. Luckily, ActionScript allows you to choose which Camera to use for capture.

When the Google plugin is installed, it exposes itself as two Camera devices; actually virtual device drivers. These devices are called 'Google Camera Adaptor 0' and 'Google Camera Adaptor 1' which you can see in the Flash Player settings, when you right click on the video. One of the device is used to display local video and the other to display the remote participant video. The Google plugin also implements the full networking protocol and stack, which I think are based on the GTalk protocol. In particular, it implements XMPP with (P2P) Jingle extension, and UDP-based media transport for transporting real-time audio/video. The audio path is completely independent of the Flash Player. In the video path: the plugin captures video from the actual camera device installed on your PC, and sends it to the Flash Player via one of the virtual camera device driver. It also encodes and sends the video to the remote user. In the reverse direction, it receives video (over UDP) from the remote user, and gives it to the Flash Player via the second of the virtual camera device drivers. The SWF application running in the browser creates two Video objects, and attaches them to two Camera object, one each for the two virtual video device, instead of attaching it to your real camera device. This way, the SWF application can display both the local and remote video in the Flash application.