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About Codecs > About Codecs - Pg. 291

pixel-by-pixel description of your DV footage into the more compact QuickTime format--and then untranslates it during playback. Each QuickTime codec works differently. Some provide spatial compression, some temporal, some both. Some are ideal for animations, and others for live action. Some work well on slower computers, others on faster ones. Some try to maintain excellent picture quality, but produce very large QuickTime fles on the disk, and others make the opposite tradeoff. Later in this chapter, you can read about each of these codecs and when to use them. In the meantime, all of this background information should help explain a few phe- nomena pertaining to converting DV movies into QuickTime fles: ·SavingaQuickTimemovietakesalongtime. It's nothing like saving, say, a word processing document. Comparing every pixel on every frame with every pixel on the next frame involves massive amounts of number crunching, which takes time. Figure 12-4: When iMovie saves a QuickTime movie, it doesn't bother writing down the description of every pixel on every frame. If there are a lot of areas that remain identical from frame to frame, the QuickTime movie doesn't remember anything more than, "Same as the previous frame." In this example, the faded portions of the picture are the areas that the QuickTime movie data doesn't describe--because they're the same as on the frst (key) frame. (At last you understand why, as you may have read in Chapter 2, using a tripod for your footage doesn't just give your movies a more professional look. By ensuring that most of the picture stays exactly the same from frame to frame, a tripod-shot video helps to produce smaller QuickTime fles.) Understanding QuickTime chapter12:fromimovietoquicktime 291