Maximumpc.com posted a guide to Playing and Transcoding Downloaded Videos
A quote from the article:
>> Ultimate Guide to Playing and Transcoding Downloaded Videos
On the following the pages we're going to show you the ins and outs of video playback. We'll start with the basics, like explaining what a file container is and why it matters, and then move on to more advanced topics, such as how to convert just about any video clip into a format that's compatible with your mobile device. We'll also show you how to handle subtitles, enable GPU Flash acceleration, and a whole lot more.
>> Ultimate Guide to Playing and Transcoding Downloaded Videos