The usual method of coding a video a few years ago was to use the object tag with a classid for IE and a nested embed tag for Firefox. The classid varied according to the file type, like .mp4 .mpg .swf and a plugin is downloaded.
You can code for Flash without a classid but the viewer needs Adobe Flash Player already, or he gets a message to install it, which wastes time. This method validates because it doesn't use a nested embed tag (the embed tag doesn't validate) . See item 2 below which uses
<object type="application/x-shockwave-flash"
style="width: 500px; height: 450px; margin: auto;"
id="VideoPlayer" data="yourvideo.swf">
instead of a classid. Most new computers now have Flash Player installed so the classid method is less necessary especially if you think your viewers will have new computers.
See http://www.wickham43.net/flashvideo.php
I'm not an expert in coding video, it's still complicated.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.