Tech Note for Nerds

From The Frame Grab Tutorial: http://tvcrit3.tvcrit.com/content/view/58/102/.


Apple's QuickTime help describes key frames:

In most cases, QuickTime uses "frame differences" to compress moving images. Frame differencing is the process of determining what information has changed from a starting frame (called a "key frame") to subsequent frames. The key frame contains all of the information for an image. Subsequent frames contain only the information that has changed.

Depending on the compressor you use, you can specify how often you want key frames to occur. If you don't have enough key frames, the quality of your movie will be very low because most frames are generated from others. On the other hand, more key frames result in a larger movie with a higher data rate. With some compressors, QuickTime automatically inserts a key frame if too much of the image has changed from one frame to the next.

From helpqt.apple.com/qthelp9w5/QuickTime.Help/pgs/65.htm


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