# 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.

- AverageLuma | v2.x | AverageLuma(clip)
- AverageChromaU | v2.x | AverageChromaU(clip)
- AverageChromaV | v2.x | AverageChromaV(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

- RGBDifference | v2.x | RGBDifference(clip1, clip2)
- LumaDifference | v2.x | LumaDifference(clip1, clip2)
- ChromaUDifference | v2.x | ChromaUDifference(clip1, clip2)
- ChromaVDifference | v2.x | ChromaVDifference(clip1, clip2)

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:

- RGBDifferenceFromPrevious | v2.x | RGBDifferenceFromPrevious(clip)
- YDifferenceFromPrevious | v2.x | YDifferenceFromPrevious(clip)
- UDifferenceFromPrevious | v2.x | UDifferenceFromPrevious(clip)
- VDifferenceFromPrevious | v2.x | VDifferenceFromPrevious(clip)

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(...)

- RGBDifferenceToNext | v2.x | RGBDifferenceToNext(clip)
- YDifferenceToNext | v2.x | YDifferenceToNext(clip)
- UDifferenceToNext | v2.x | UDifferenceToNext(clip)
- VDifferenceToNext | v2.x | VDifferenceToNext(clip)

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(...)

- YPlaneMax | v2.x | YPlaneMax(clip, float threshold)
- UPlaneMax | v2.x | UPlaneMax(clip, float threshold)
- VPlaneMax | v2.x | VPlaneMax(clip, float threshold)
- YPlaneMin | v2.x | YPlaneMin(clip, float threshold)
- UPlaneMin | v2.x | UPlaneMin(clip, float threshold)
- VPlaneMin | v2.x | VPlaneMin(clip, float threshold)
- YPlaneMedian | v2.x | YPlaneMedian(clip)
- UPlaneMedian | v2.x | UPlaneMedian(clip)
- VPlaneMedian | v2.x | VPlaneMedian(clip)
- YPlaneMinMaxDifference | v2.x | YPlaneMinMaxDifference(clip, float threshold)
- UPlaneMinMaxDifference | v2.x | UPlaneMinMaxDifference(clip, float threshold)
- VPlaneMinMaxDifference | v2.x | VPlaneMinMaxDifference(clip, float threshold)

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 $