Microsoft is at the Sundance Film Festival for the coming week demonstrating one of their main contributions to HD DVD technology: HDi, the interactivity layer.

According to this post at Andy Pennel’s developer blog, representatives from the HDi team will be at the Microsoft House for some demos and movie screenings. This is intended for independent filmmakers who may be interested in learning how to take advantage of HDi in their disc releases.

We’ve talked about HDi a few times at the site, and it’s one of the features that demonstrates how the HD DVD platform was well thought out from the very beginning. HDi interactivity is mandated on all HD DVD players, and it’s such a cool and next-gen kind of feature. On conventional DVDs, you have to pretty much stop the whole movie just to revisit the menu and change your various viewing options, but that’s not so on HD DVDs where you can do all of these things while the movie continues to play. You can change viewing options, select a chapter to skip ahead to, or even change your mind and resume viewing, all without interrupting the main flow of the movie.

Some discs have bonus content that augments the viewing experience. For example, in The Kingdom, you can pull up brief explanations about the cultural and political aspects of things that come up in the plot. In The Bourne Ultimatum and on Heroes, you can look up some story related items such as character profiles.

Web-enabled interactivity has also been interesting. Harry Potter and the Order of the Phoenix has a “Live Community Screening” mode where friends can watch together from their own homes, and even send each other text messages in a manner similar to multiplayer video games. The simpler web implementations have been more about downloading bonus content, purchasing things like ring tones, or taking quizzes and comparing your results with other viewers.

The equivalent functionality has only recently started rolling out on the Blu-ray format in a few phases, and they’re still catching up in that regard. In fact, many Blu-ray owners are in for some disappointments in the months ahead when new discs start coming out with interactivity features that Blu-ray players purchased as recently as last month can never take advantage of. The only known solution for this problem is to have been using a PS3 as your Blu-ray player because it’s so upgradeable.

Many Blu fans and officials scoffed at the usefulness of interactivity features when they weren’t yet available on their players. However, since it was a major Blu-ray theme at CES a couple of weeks ago, I’m sure all of these people will gradually start singing the praises of interactivity as their new players and related movies start coming out in the months ahead.

Whenever and however interactivity comes their way, at least they’ll get a chance to see what HD DVD owners have already been enjoying for several months.

• Microsoft and HDi at Sundance
• Sundance Film Festival (Jan 17-27)