Studios are busy adding extra features to TV-DVDs. A few of them are even insightful.

No wonder people stayed home from movie theatres this past holiday season: they’ve been watching complete seasons of TV shows on DVD, which have become a huge part of the home video industry and a popular holiday gift. And as TV on DVD becomes big business, studios are putting more resources into creating extra features for these releases. It’s not easy to create special features for a TV episode: TV shows are produced so fast that the creators may not necessarily remember much about how they were made. But still they try. Some of these features are insightful; others are just there so that there will be something to advertise on the back of the box. But most TV-on-DVD special features fall into three basic categories.

Audio commentaries: As with feature films, the most common special feature for TV shows is the audio commentary, in which the participants talk over an episode — mostly about how much they love everything; if you think Hollywood writers are bitter and cynical, listen to the commentary tracks for episodes of Seinfeld, where creators Larry David and Jerry Seinfeld have little to say except "Boy, that was a great show" and "What show is this? This is the end of season what?"

Sometimes a TV episode can give rise to a truly insightful commentary, when you get a writer or producer who really has an interest in analyzing the episode for us. On an episode in Season Four of The Dick Van Dyke Show, Garry Marshall (Pretty Woman) goes into specific details about all aspects of production, even the way loud clothing on the actors can detract from the comedy, and has so much to say that he goes on talking for five minutes after the episode ends. And Buffy the Vampire Slayer writer-producer Joss Whedon is beloved by geeks everywhere for his near-scholarly comments on his own episodes.

Few shows have commentaries on every episode, other than The Simpsons and Futurama, where creator Matt Groening insists on gathering his crew to comment on everything. Most season sets have commentaries on two or three of the best episodes, though sometimes a bad episode will sneak in for variety’s sake. The creators of Batman: The Animated Series chose to do a commentary on the episode in which Batman battles an evil farmer, and while they defend the episode a little, they mostly make fun of the premise: "You gotta be kidding me — Batman’s fighting giant chickens?"

Making-of documentaries: Some shows have, in addition to or instead of commentaries, a mini-documentary in which the creators and stars explain how the show was made. All these making-ofs tell exactly the same story: the creators had an idea; they tested many actors for the leads, and the ones they wound up with were perfect in every way; the show made it to the air but took time to find an audience; the show found an audience and made everybody rich; the end. If the show is a cult flop, that last part is replaced by a segment about how the network never really gave it a chance. However, some recent releases have found new and even insightful approaches to making-of segments. The DVD releases of Seinfeld preface most episodes with "Inside Looks" in which the participants recall how they were made. Shows like Buffy and the current hit Lost feature informal discussions between the cast and crew members. And the ’80s romantic whodunit Remington Steele, whose DVD releases have been so successful that they have inspired star Pierce Brosnan to plan a feature film based on the show, uses 10-minute featurettes to analyze specific aspects of the show’s appeal: the romance, the stunts, and, of course, Doris Roberts.

Deleted scenes: As the DVD release becomes an increasingly essential part of a TV show’s life, more and more shows are saving the scenes they had to cut. Some producers even put deleted scenes back, taking advantage of their freedom from commercial breaks to make the episodes longer and, in some cases, better than they could be on network TV. The creators of Friends did "extended" versions of many episodes for the DVDs. And the pilot of Arrested Development on DVD features six minutes of extra material and even un-bleeps some of the swear words — which, strangely enough, is less funny than the network’s bleeped version.

This is only a partial guide to TV-on-DVD features — we haven’t even talked about blooper reels. But whether they are insightful or frightful, they all serve one useful purpose. Without them, TV writers would never have a chance to let the public know who they are.