The page http://www.w3schools.com/html/html_videos.asp incorrectly describes the technique being recommended. The page has "The example below uses the <video> element and tries to play the video either as MP4 or OGG. If that fails, the code "falls back" to try the <embed> element:" But the code that follows the statement takes a 3-step approach.
The description should be:
The example below uses the <video> element and tries to play the video either as MP4 or OGG. If that fails, the code "falls back" to try the <object> element to play the video as MP4. And if that fails, the code "falls back" to try the <embed> element to play the video as SWF:
There is a similar error in the corresponding page about playing audio.