Dive into HTML5 ( diveinto.html5doctor.com ) is an online book by Mark Pilgrim that is a great resource for learning about many features of HTML5. The book gives a history of HTML5, and includes chapters on drawing, video, geolocation, local storage, and offline apps. There are a few features of HTML5 (and related APIs) that it does not describe, including Web Workers and Web Sockets.
HTML5 Rocks http://www.html5rocks.com/en/tutorials/video/basics/
Dive into HTML5
This online book has a good history of HTML5 video, but the part about which browsers support which video formats and codecs is out of date. You don't need to know which browsers support the different video formats. You don't need to know or read the parts of this web site that tell how to encode video.
Mozilla Developer Network on HTML5 media, including audio: https://developer.mozilla.org/en-US/docs/Web/Guide/HTML/Using_HTML5_audio_and_video
HTML5 Canvas Tutorials http://www.html5canvastutorials.com/tutorials/html5-canvas-element/
Dive into HTML5 diveinto.html5doctor.com/canvas.html
Here are a few links to web pages that have information about video codecs, including browser support for codecs:
Keep in mind that it can be difficult to determine if a particular browser supports a particular video codec. The charts and information included in some of the links above can be helpful, but they aren't necessarily up to date or well-explained. For example, diveinto.html5doctor.com says that IE 9.0+ will play WebM, but from what I have read, it looks like it requires the installion of software components that aren't included with the browser. You don't have to know which browsers support which codecs for quizzes or tests.