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Understanding QuickTime Quality > QuickTime Movies and Color Depth - Pg. 15

QuickTime Pro: Making It All Happen QuickTime Movies and Frame Rate 15 QuickTime movies--just like their analog counterparts--are actually a series of still images that are slightly different from one another. As these images are shown onscreen, you see the illusion of motion. QuickTime is really just the digital equivalent of the flipbook. The faster these images "flip" on the screen, the smoother and more lifelike the movie appears. The speed at which the images that make up the movie are displayed (are changed) is called the frame rate. As with resolution, there is a trade-off between the quality of the movie and the resources it requires to be played. The higher the frame rate, the smoother and better the movie appears. However, QuickTime movies with higher frame rates also require more processing power to view and the file sizes are larger. Similar to resolution, you want to use the highest frame rate possible for the file size that you can tolerate. NOTE While there is no one standard frame rate, there are standard frame rates that are used. For example, the standard frame rate for QuickTime movies that you create with iMovie is roughly 30 frames per second (fps). This is about the same as the frame rate you will see on television in the United States (Europe uses a slightly different standard). Other media, such as animation, might use a lower frame rate. For example, games are often played at 12 to 20 fps. When your Mac "flips" to the next image (frame) in a movie, it really only changes the individual pixels that are different from one frame to the next. Often, most of the pixels don't change from one frame to the next. The frame that is used as the "base" from which the following frames are measured is called the key frame . Using key frames more frequently improves the movie's image quality be- cause the motion appears to be more fluid. However, having more key frames also increases file size because more information is required.