Ripping your own DVDs to H.264/MP4 is all well and good. But what if you've previously taken the time and effort to convert DVDs to another less compatible format, such as Windows Media Video (WMV)? In this case, you have two options. You can either re-rip your DVD collection using the superior and more compatible H.264/MP4 format, as outlined in my article, How to Rip DVDs. Or you can attempt to convert your existing videos to H.264/MP4.
My recommendation is to try the latter first: After all, the worst case scenario is that the converted files aren't of high enough quality to save, in which case you can fall back to re-ripping. (Or simply leave things as they are.) But in my experience, WMV-to-H.264 conversions usually work out just fine, especially if the source file is of sufficient quality.
To convert a video from WMV (or from almost any other video format), you can again use the free and excellent Handbrake utility. That's right: In addition to being an excellent DVD ripper, Handbrake can also convert video files to H.264/MP4, using the same high quality and broadly compatible "Universal" preset that you'd use for DVD ripping.
Here's how it works.
Start Handbrake and click the Source button. But now, instead of choosing a DVD as the source, click Video File.
Using the File Open dialog that appears, navigate to the video file you wish to convert and click Open. Note that while you can only select one file at a time this way, you can use Hanbrake's queuing feature to queue up multiple files for conversion and have them all happen sequentially.
In Handbrake, ensure that the Apple, Universal preset is selected. Then, click the Start button. As with DVD ripping, a command line window will open and provide you with a progress indicator as the file converts.
A couple of notes about this process. It only works with non-protected video files, of course. So if you purchased a movie or TV show from Apple iTunes, Zune Marketplace, or another source, this won't be able to convert such a file. Also, video conversion does not require a DVD decrypter like AnyDVD.