By getUserMedia() method we can get the audio and video stream in codec format through the microphone and webcam respectively.
After converted this codec format in url of user video, it would assigned into source tag under the video element to make complete video.
So the video we are getting from getUserMedia() api is like other usual video eg:-
<video width="320" height="240" controls>
<source src="http://www.w3schools.com/tags/movie.mp4" type="video/mp4">
<source src="http://www.w3schools.com/tags/movie.ogg" type="video/ogg">
Your browser does not support the video tag.
</video>
http://jsfiddle.net/ez3pA/2/
So you can do various things about video and canvas element together. We can get good examples of this on a site http://html5doctor.com/video-canvas-magic/