The interactive nature of the Web often requires that sites feature embedded video content. At one point, there was no standard way to accomplish this goal. Each Web master took a different approach to embedding video clips, so visitors were often expected to spend a fair amount of time installing various plug-ins if they wished to be able to see all of the applicable content on the site.
When Flash® video arrived on the scene, it quickly became the standard for video content online. The program was installed on nearly every computer, so visitors didn't need to waste time searching for a number of different plug-ins. Unfortunately, Adobe® Flash® uses large amounts of processor time and slows down your general computing speed in a significant way. Windows Media®, Quicktime®, and Real Media video formats can be used instead of Flash, but support for these formats is not as widespread.
The video tag is new in HTML 5. If you're planning to make a Web site using this tag, keep in mind that you can write text between the start and end tags that will show older browsers they do not support this tag. Unfortunately, visitors who expect to see video on your site are likely to be very frustrated when they receive this message. People generally like to stick with the technology they are the most comfortable with, so they may resent being forced to upgrade browsers in order to properly view your Web site.
If you believe a significant number of your site visitors will be using older browsers, using Flash® to embed video onto your Web pages may be the best approach. When using the video tag to add video clips to your Web pages, you can set your code to automatically degrade to a Flash® fallback if the visitor's browser doesn't support the video tag. The downside of this approach is that you will need to upload MPEG4, Ogg, and FLV versions of every embedded video clip to your servers.