This is an example file for an HTML5 Video tutorial: http://edutechwiki.unige.ch/en/HTML5_audio_and_video
Look at the source if you don't want to read the EduTechWiki article ...
In this section we first will display different video formats. That way you can test your browser. We finally show how to define alternatives.
This example wouldn't work in a browser like IE9 that doesn't support Ogg
This example wouldn't work in a browser like Firfox that doesn't support mp4
This example wouldn't work in a browser like IE9 that doesn't support webm
This example should work in most current modern web browsers, since it defines the three most popular alternatives. However, defining a container format may not be enough, since each container may include different codecs. I.e. there are quality variants for mp4 and its better ones may not display in certain browsers/devices.