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Usually only few of the spatially closest known samples are used for the extrapolation. Formats that operate sample by sample like [[Portable Network Graphics]] (PNG) can usually use one of four adjacent pixels (above, above left, above right, left) or some function of them like e.g. their average. Block-based (frequency transform) formats prefill whole blocks with prediction values extrapolated from usually one or two straight lines of pixels that run along their top and left borders.
The term intra-frame coding refers to the fact that the various lossless and [[lossy compression]] techniques are performed relative to information that is contained only within the ''current frame'', and ''not relative'' to any other frame in the video sequence. In other words, no temporal processing is performed outside of the current picture or frame. Non-intra coding techniques are extensions to these basics. It turns out that this block diagram{{clarify|reason=too much imagination required to resolve "this"|date=January 2022}} is very similar to that of a JPEG still image video encoder, with only slight implementation detail differences.
Inter frame has been specified by the [[CCITT]] in 1988–1990 by [[H.261]] for the first time. H.261 was meant for teleconferencing and ISDN telephoning.
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