I have a video in .avi format that I would like to place on a website, however I am concerned that many web users will not have the appropriate Microsoft plugin. I would like to be able to check if the browser has the plugin and serve the .avi video. If they do not have the plugin I would like to present them the youtube version.
The Windows Media Player may or may not play that .avi. A better format for Web would be a .wmv. Every Windows machine will already have the Media Player, Macs....not so much.
I'm curious, why do you want to show it in the Windows Media Player version and not just the YouTube version? Can't say I blame you.
An alternative would be to create a .flv version, use a Flash player, and call it good. Creating your own .flv version would allow you to use a higher bit rate than YouTube, resulting in a higher quality video.
The best way is to convert your avi into flv/swf. You can try Moyea flash video MX.
"It can convert video to Flash by creating a Flash Video player (SWF file) for the generated FLV file. It also provides various playback skins with different styles for the SWF file, and automatically creates an HTML page to display the SWF file. With Flash Video MX, you can add special effects, movie beginning and movie end, edit frame rate and audio effect, add multi-functional control bars to the generated Flash files, and even replace the original audio with your favorite music in the output Flash. "
You can search "flash video mx pro" on google.com for more info.