HTML5 media plugin

I enabled the HTML5 media plugin, then I went to Chrome and IE browser to open a video file. it still let me install "QuickTime" plugin. from the code, I can see no matter I use or not the HTML5 media plugin, it uses "embed" tag which to use QuickTime". Do I need to change "embed" to "video" tag in the code?
Many thanks.

The HTML5 Media plugin will only work on some kinds of files, the ones that are supported by the browsers and/or can be filled in with the Flash component the plugin uses.

What was the extension or MIME type of the file that's not working? You can change the extensions and types in the Configure page for the plugin, but something like .avi isn't going to work on many or most platforms.