![]() ![]() This number of frames is the "GOP length". Because of this, most compression schemes have a maximum number of frames over which they will assume no changes, after which the entire frame is updated and the process starts again. This means that errors build up from frame to frame, and would after a while become unacceptable. However, this thresholding invariably means that some very subtle movements are incorrectly assumed to be noise, and ignored. Because of this, it is necessary to apply a threshold below which small changes in frame data are assumed to be noise, not real motion, and need not be encoded. However, real world images (except some computer generated ones) invariably contain noise, film grain, tiny camera motions or changes in lighting, so in a mathematical sense absolutely all of the image is changing constantly by a very small amount. A compression codec could choose to encode the background image once, and store only the areas which move. The graphic may not change at all for many seconds, whereas the presenter will be moving around. Consider the example of a weather presenter keyed over a computer-generated graphic. The "group of pictures" idea has its roots in compressed animation formats like those used in Amiga computers in the late 80s and early 90s.Ĭompression codecs like MPEG-1, MPEG-2, h.264, and others, use the similarity between frames to achieve better compression performance. Is this just so each frame has less info and really just records the changes from previous frame instead of a whole new frame therefore its being compressed?ĭoes it just make a difference in editing or can you see the difference as well? Edited Decemby Shidan Saberi Because each frame has more of its own independent data instead of a set up frames which just record the changes. hypothetical, of course) 14 frames of nothing! Later on, in the editing suite a computer would "reconstruct" that missing data by adding the changes (in this case nothing) to the original fame to make up the information.Īhhh, ok its starting to click. In a GoP codec, you'd have 1 full frame image and then (assuming nothing changes all. With an iFrame codec, and a static shot, you'd wind up with, let's say, 15 frames of white wall, each one a full photo. ![]() in a GoP codec, the 1st frame is a full image, then the subsequent frames (for however many they wish to set it) just records the differences- these frames are later reconstructed from this data. Think of it like this in an iFrame codec, each frame is a still image. ![]()
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