About Digital Video Technology

In October 2005, Apple unveiled the long-awaited iPod 5Gthe first model in the family that supported the playback of video files as well as music and photos. This new device sported a larger color screen than its predecessors and a set of new features in the software interface that made navigating and playing your music videos, home movies, and TV episodes as easy as playing your music.

Video, however, threatened to complicate the elegant interoperability of iTunes and the iPod. Until that time, the function of iTunes was clearto organize, buy, and play your music. The very name "iTunes" suggested that the focus of the software was firmly on music, and the idea of adding video features to it gave Apple a real challenge.

It was a challenge worth meeting. Beginning with an upgrade to the iTunes Music Store in mid-2004 that saw music videos playing in areas of the store where you could purchase the featured song while you watched the video, and continuing on with integrated video playback and downloadable music videos and movie trailers in iTunes 4.8 a year later, Apple slowly made iTunes and video comfortable with each other. Finally, with the release of the iPod 5G, Apple made it clear that video was to be an integral part of the iTunes/iPod experience. Patrons of the iTunes Music Store could purchase music videos, short films, or TV show episodes for $1.99 each, and they could organize them and play them back in iTunes using a new visual navigation screen. Owners of the new iPod could sync these videos with the rest of their digital media in iTunes and take their favorite TV shows with them on the bus or train.

The video playback technology in iTunes and the iPod depends on the MPEG-4 and H.264 encoding standards built into the QuickTime multimedia architecture that underlies iTunes on both the Windows and Mac platforms and is integrated into Mac OS X. MPEG-4 files contain the same DRM technology found in purchased AAC files, restricting purchased videos to the same authorized computers that can play music bought by the same person.

The encoding algorithms behind iTunes' MPEG-4 files ensure that the videos you buy have the same frame rate that you would see on broadcast TV, and the clarity of the image is at least as good as you would expect to see in a show recorded on TiVo. However, the size of the picture in a purchased video is usually 320x240 pixels, a smaller size than on normal TV. This means that the videos you buy from the iTunes Music Store won't look quite as clear as the same shows on your TV screen.

Key Terms

Frame rate The rate at which the sequence of still frames that make up a video is presented; broadcast TV uses a frame rate of about 30 frames per second, whereas feature films use 24 frames per second.

Pixels Individual dots on your screen that make up an image.

The reason for this compromise has to do with the limitations on current computer technology. A half-hour (22 minutes without commercials) episode of The Office or Drawn Together consumes about 100MB of space on your hard disk, and an hour-long (45-minute) episode of Lost or Battlestar Galactica runs about 200MB. (Cable shows like Sleeper Cell that don't take time out for commercials run the full 60 minutes, making their files even larger.) This means that your 240GB disk will lose about 1 percent of its capacity with every full season of hour-long shows that you purchase. That might not sound like much, but don't forget: These videos are also intended to be played on your iPod. A 60GB iPod will have to devote 4 percent of its capacity to that same season of Lost, and that much space is no longer available for your music or photos.

Furthermore, you must take into account the time it takes to download each of these videos. Short music videos hardly take any longer to download than a song or two; but a full half-hour TV show can tie up your Internet connection for minutes on endand that's if you're on broadband. If you're using a modem, you can expect to be downloading for hours before you've received the video you purchased.

Finally, there's the issue of backups. The iTunes Music Store, as a rule, does not allow customers to download more than one copy of a purchased song or video. That means that when you've bought and downloaded a file, that file is all you've gotif it gets deleted from your computer, you can't get it back. That's why you should consider an appropriate backup solution (such as the ones discussed in Back Up Your Music to CD or DVD). This type of backup is fine for music, but when it comes to videos, your backup solution, such as a writable DVD, might not be big enough to hold all your purchased TV shows. More heavy-duty backup methods such as external hard drives might not be cost-effective for many users. This limitation means that keeping your whole video library on your computer simply isn't feasible yet, although it is feasible for music collections.

Things are bad enough just with the 320x240 video files currently available through the iTunes Music Store. Imagine, though, if Apple were to start selling higher-definition video content, with an image size of 640x480 (about what's available in broadcast TV). This would quadruple the amount of data required to produce each video file; a half-hour TV episode would be 400MB, and a single episode of Sleeper Cell would take up a whole gigabyte.

The good news is that technology keeps marching forward. Soon we'll all have hard drives ten times the size they are now, broadband Internet connections that can download hundreds of megabytes in the blink of an eye, and HD-DVD or Blu-Ray optical drives that can solve our backup needs for years to come. Until that happens, though, we'll have to be content with our 320x240 videos.