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mation that describes each frame. True, the picture deteriorates as a consequence, but the resulting QuickTime movie fle is a tiny fraction of its original size. The following section describes this compression business in much greater detail. The bottom line is that by combining these three techniques, iMovie can turn your 10 GB DV movie into a 3 MB fle that's small enough to email or post on your Web page. The resulting movie won't play as smoothly, fll as much of the screen, or look as good as the original DV footage. But your viewers won't care. They'll be delighted to be able to watch your movie at all, and grateful that the fle didn't take hours to download. (And besides, having already been exposed to QuickTime movies, most know what to expect.) Tip: The later the QuickTime version your Mac contains, the better and faster the movie-exporting process becomes. Mac OS X's Software Update feature is supposed to alert you every time a new version becomes available (if you have it turned on in System Preferences). Understanding QuickTime A Crash Course in Video Compression The following discussion explores some technical underpinnings of QuickTime technology. It may take you a few minutes to complete this behind-the-scenes tour of how a computer stores video. But without understanding the basics, iMovie's QuickTime-exporting options will seem utterly impenetrable. Spatial compression Suppose you overhear a fellow Mac fan telling her husband, "Would you mind run- ning to the grocery store? We need an eight-ounce box of Cajun Style Rice-A-Roni, and an eight-ounce box of Cajun Style Rice-A-Roni, and also an eight-ounce box of Cajun Style Rice-A-Roni." You'd probably assume that she's enjoyed a little too much of that new-computer smell. Why didn't she just tell him to pick up "three boxes" of it? When it comes to storing video on a hard drive, your Macintosh faces the same issue. When storing a picture fle, it must "write down" the precise color of each pixel of each frame. It could, of course, store the information like this: · Top row, pixel 1: Beige · Top row, pixel 2: Beige · Top row, pixel 3: Beige ...and so on. Clearly, this much information would take a lot of space and a lot of time to reproduce. Fortunately, when Apple engineers were designing QuickTime in the 1980s, it occurred to them that the individual dots in solid-colored areas of the picture don't need to be described individually. That top row of pixels could be represented much more eff- ciently, and take up a lot less disk space, if the Mac were simply to write down: · Top row: 60 consecutive pixels of beige chapter12:fromimovietoquicktime 289