AviSynth Syntax - Runtime functions

These are the internal functions which are evaluated at every frame. They can be used inside the scripts passed to runtime filters (ConditionalFilter, ScriptClip, FrameEvaluate) to return information for a frame (usually the current one). When using these functions there is an implicit last clip (the one that is passed to the runtime filter). Thus, first parameter doesn't have to be specified; it is replaced by the last clip.

This group of functions return a float value with the average pixel value of a plane (Luma, U-chroma and V-chroma, respectively). They require that clip is in YV12 colorspace and ISSE.
Examples:
threshold = 55
luma = AverageLuma()
luma < threshold ? Levels(0, 1.0 + 0.5*(threshold - luma)/threshold, 255, 10, 255) : last
This group of functions return a float value between 0 and 255 of the absolute difference between two planes (that is two frames from two different clips). Either the combined RGB difference or the Luma, U-chroma or V-chroma differences, respectively. They require that clip is in YV12 colorspace and ISSE.
Examples:
ovl = Overlay(last, mov_star, x=some_xvalue, y=some_yvalue, mask=mov_mask)
ldif = LumaDifference(ovl) # implicit last for clip1
udif = ChromaUDifference(Tweak(hue=24), ovl)
...


The next two groups of functions should be quite handy for detecting scene change transitions:

This group of functions return the absolute difference of pixel value between the current and previous frame of clip. Either the combined RGB difference or the Luma, U-chroma or V-chroma differences, respectively.
Examples:
scene_change = YDifferenceFromPrevious() > threshold ? true : false
scene_change ? some_filter(...) : another_filter(...)
This group of functions return the absolute difference of pixel value between the current and next frame of clip. Either the combined RGB difference or the Luma, U-chroma or V-chroma differences, respectively.
Examples:
# both th1, th2 are positive thresholds; th1 is larger enough than th2
scene_change = YDifferenceFromPrevious() > th1 && YDifferenceToNext() < th2
scene_change ? some_filter(...) : another_filter(...)
This group of functions return statistics about the distribution of pixel values on a plane (Luma, U-chroma and V-chroma, respectively). The statistics are, in order of presentation: maximum, minimum, median and range (maximum - minimum difference).
threshold is a percentage, stating how many percent of the pixels are allowed above or below minimum. The threshold is optional and defaults to 0.
Examples:
# median and average are close only on even distributions; this can be a useful diagnostic
have_intense_brights = YPlaneMedian() - AverageLuma() < threshold
...
# a simple per-frame normalizer to [16..235], CCIR, range
Levels(YPlaneMin(), 1.0, YPlaneMax(), 16, 235)

Back to Internal functions.

$Date: 2008/04/20 19:07:34 $