# ConditionalFilter

Table of contents

- ConditionalFilter
  - ConditionalFilter
  - ConditionalSelect
  - ScriptClip
  - FrameEvaluate
  - ConditionalReader
  - Runtime Functions
    - Other internal functions
  - Advanced conditional filtering: part I
  - Advanced conditional filtering: part II
  - Advanced conditional filtering: part III

## ConditionalFilter

`ConditionalFilter` (clip testclip, clip source1, clip source2, string expression1, string operator, string expression2, bool “show”)

`ConditionalFilter` returns source1 when the condition formed by “expression1+operator+expression2” is met for current frame, otherwise it returns source2. If any function in expression1 or expression2 is not explicitly applied to a clip, it will be applied on testclip. The audio is taken from source1.

An example. This will choose frames from vid_blur when the average luma value of a frame is less than 20. Otherwise frames from vid will be returned.

    vid = AviSource("file")
    vid_blur = vid.Blur(1.5)
    ConditionalFilter(vid, vid_blur, vid, "AverageLuma()", "lessthan", "20")

Adding show=”true” will display the actual values on the screen.

The strings expression1 and expression2 can be any numeric or boolean expressions, and may include internal or user functions, as well as some additional functions which are predefined (the Runtime Functions) and the special runtime variable current_frame (the framenumber of the requested frame).

The string operator can be “equals”, “greaterthan” or “lessthan”. Or “=”, “>” or “<” respectively.

## ConditionalSelect

`ConditionalSelect` (clip testclip, string expression, clip source0, clip source1, clip source2, … , bool “show”)

`ConditionalSelect` returns each one frame from several source clips based on an integer evaluator. If the expression evaluates to the integer j (starting at zero), the frame from the j-th source clip is returned.

This will return a frame from vid_blur2 when the average luma value of a frame (of vid) is less than 15, will return a frame from vid_blur when the average luma value of a frame (of vid) is higher than 15 but smaller than 25. Otherwise a frame from vid will be returned.

    vid = AviSource("file")
    vid_blur = vid.Blur(1.0)
    vid_blur2 = vid.Blur(1.5)
    ConditionalSelect(vid, "luma_av = AverageLuma()"+chr(13)+"luma_av <
    25 ? (luma_av < 15 ? 2 : 1) : 0", vid, vid_blur, vid_blur2)

    # Adding show="true" will display the actual values on the screen.

If a frame is requested from a non-existing source clip (say the expression evaluates to -1 or 3 in the example above, where 3 source clips are supplied), the frame of the testclip will be returned.

Audio from “testclip” is passed through untouched.

## ScriptClip

`ScriptClip` (clip, string filter, bool “show”, bool “after_frame”)

`ScriptClip` returns the clip returned by the filter evaluated on every frame. The string filter can be any expression returning a clip, including internal or user clip functions, and may include line breaks (allowing a sequence of statements to be evaluated). Also, also some functions which are predefined (the Runtime Functions) and the special runtime variable current_frame (the framenumber of the requested frame) can be used in the filter expression. Adding show=”true” will display the actual values on the screen.

Some examples:

    # This will print the difference from the previous frame onto the current one:
    clip = AviSource("c:\file.avi")
    ScriptClip(clip, "Subtitle(String(YDifferenceFromPrevious))")

    # This will apply blur on each frame based on the difference from the previous.
    # This will also show how errors are reported on some frames :)
    clip = AviSource("c:\file.avi")
    ScriptClip(clip, "Blur(YDifferenceFromPrevious/20.0)")

    # This will apply temporalsoften to very static scenes, and apply a _variable_ blur on moving scenes.
    # Blur is now capped properly. We also assign a variable - and this is why a line break is inserted:
    function fmin(float f1, float f2) {
      return (f1<f2) ? f1 : f2
    }
    clip = AviSource("c:\file.avi")
    T = clip.TemporalSoften(2, 7, 7, 3, 2)
    ScriptClip(clip, "diff = YDifferenceToNext()"+chr(13)+"diff>2.5 ?
    Blur(fmin(diff/20, 1.5)) : T")

    # Shows the frame-number in a clip:
    ScriptClip("subtitle(string(current_frame))")

    # Shows 'frame = the frame-number' in a clip:
    ScriptClip("""subtitle("frame = " + string(current_frame))""")

In v2.55 an after_frame=true/false option to is added. This determines if the script should be evaluated before (default operation) or after the frame has been fetched from the filters above.

“Restrictions”: the output of the script MUST be exactly like the clip delivered to `ScriptClip` (same colorspace, width and height). Your returned clip is allowed to have different length - but the length from “clip” is always used. Audio from “clip” is passed through untouched. For two very different sources (MPEG2DEC3 and AviSource) - you might run into colorspace mismatches. This is known quirk.

## FrameEvaluate

`FrameEvaluate` (clip clip, script filter, bool “after_frame”)

Similar to `ScriptClip`, except the output of the filter is ignored. This can be used for assigning variables, etc. Frames are passed directly through from the supplied clip.

In v2.53 an `after_frame=true/false` option to is added. This determines if the script should be evaluated before (default operation) or after the frame has been fetched from the filters above.

## ConditionalReader

This filter allows you to import arbitrary information into a selectable variable.

See the dedicated ConditionalReader page.

## Runtime Functions

These are the internal functions which are evaluated every frame.

These will return the average pixel value of a plane (require YV12, ISSE):
`AverageLuma` (clip)
`AverageChromaU` (clip)
`AverageChromaV` (clip)
These return a float value between 0 and 255 of the absolute difference between two planes (require YV12, ISSE):
`RGBDifference` (clip1, clip2)
`LumaDifference` (clip1, clip2)
`ChromaUDifference` (clip1, clip2)
`ChromaVDifference` (clip1, clip2)

When using these functions there is an “implicit last” clip (first parameter doesn’t have to be specified), so the first parameter is replaced by the testclip.

These should be quite handy for detecting scene change transitions:
`RGBDifferenceFromPrevious` (clip)
`YDifferenceFromPrevious` (clip)
`UDifferenceFromPrevious` (clip)
`VDifferenceFromPrevious` (clip)
`RGBDifferenceToNext` (clip)
`YDifferenceToNext` (clip)
`UDifferenceToNext` (clip)
`VDifferenceToNext` (clip)

    # This will replace the last frame before a scenechange
    # with the first frame after the scenechange:
    ConditionalFilter(last, last, last.trim(1,0), "YDifferenceToNext()", ">", "10", true)

### Other internal functions

`YPlaneMax` (clip, float threshold)
`UPlaneMax` (clip, float threshold)
`VPlaneMax` (clip, float threshold)
`YPlaneMin` (clip, float threshold)
`UPlaneMin` (clip, float threshold)
`VPlaneMin` (clip, float threshold)
`YPlaneMedian` (clip)
`UPlaneMedian` (clip)
`VPlaneMedian` (clip)
`YPlaneMinMaxDifference` (clip, float threshold)
`UPlaneMinMaxDifference` (clip, float threshold)
`VPlaneMinMaxDifference` (clip, float threshold)

Threshold is a percentage, on how many percent of the pixels are allowed above or below minimum. The threshold is optional and defaults to 0.

If you understand the stuff above, you can proceed with “advanced conditional filtering”, which tells you a little bit more about conditional filtering.

## Advanced conditional filtering: part I

You will have to know a few things about the functionality of AviSynth to understand this section: Scripts are parsed from top to bottom, but when a frame is requested the last filter is actually being invoked first, requesting frames upwards in the filter chain. For example:

    AviSource("myfile.avi")
    ColorYUV(analyze=true)
    Histogram() When opening the script in Vdub the following happens

- When Vdub requests a frame, AviSynth requests the frame from Histogram.
- Histogram requests a frame from ColorYUV,
- ColorYUV requests a frame from AviSource, which produces the frame, and delivers it to ColorYUV.
- ColorYUV processes the image and sends it on to Histogram, which returns it to Vdub.

So the filter chain basically works backwards (the output is ‘pulled’ from below rather than ‘pushed’ from above), which gives each filter the possibility to request several frames from the source above. Conditional filters however, need to evaluate scripts before they request frames from the filter above, because they need to know which filter to call. Another important issue is that run-time scripts are evaluated in the same context as the main script. Hence only global defined variables in the conditional filter ‘environment’ can be used inside a function (and vice versa). Have a look at the following script:

    v = AviSource("E:\Temp\Test3\atomic_kitten.avi").ConvertToYV12

    function g(clip c)
    {
      global w = c
      c2 = ScriptClip(c, "subtitle(t)")
      c3 = FrameEvaluate(c2, "t = String(text)")
      c4 = FrameEvaluate(c3, "text = YDifferenceFromPrevious(w)")
      return c4
    }

    g(v)

This filter chain works like this:

- When Vdub requests a frame, AviSynth requests a frame from the second FrameEvaluate, the last filter in the chain generated by g().
- The second FrameEvaluate evaluates YDifferenceFromPrevious(w), which leads to the following actions:
  - YDifferenceFromPrevious requests a frame from ConvertToYV12;
  - ConvertToYV12 requests a frame from AviSource, which produces the frame, and delivers it to ConvertToYV12;
  - ConvertToYV12 processes the image and returns it to YDifferenceFromPrevious;
  - YDifferenceFromPrevious requests a second frame from ConvertToYV12, which is obtained in a similar way to the first;
  - It then compares the two frames to calculate its result which it delivers to FrameEvaluate.
- FrameEvaluate assigns this value to the variable text.
- After this a frame is requested from the first FrameEvaluate.
- The first FrameEvaluate, after evaluating String(text) and assigning this value to the variable t, requests a frame from ScriptClip.
- ScriptClip sets last to the result of ConvertToYV12(), evaluates Subtitle(t) (creating a new, temporary, filter chain), and requests a frame from it.
  - Subtitle requests a frame from ConvertToYV12;
  - ConvertToYV12 requests a frame from AviSource, which produces the frame, and delivers it to ConvertToYV12;
  - ConvertToYV12 processes the image and returns it to Subtitle;
  - Subtitle adds the specified text to the frame and delivers the result to ScriptClip.
- ScriptClip returns the subtitled frame to the first FrameEvaluate.
- In turn this frame is returned to the second FrameEvaluate, and hence to Avisynth which returns it to VDub.

Notice how the addition of run-time filters and run-time functions makes the interactions between different parts of the filter chain more complex. This added complexity is managed internally by Avisynth, so you needn’t worry about it. However, care is required when setting and using variables, as the order of events can be less obvious to the script writer (you!).

As can be seen, w is defined as a global variable. This way we can use it later in the script in the conditional environment. If we want to use the variables t and text in a different function (inside or outside the conditional environment), they must also be defined as global variables. Thus for example:

    v = AviSource("E:\Temp\Test3\atomic_kitten.avi").ConvertToYV12

    function g(clip c)
    {
      global w = c
      c2 = ScriptClip(c, "subtitle(t)")
      c3 = FrameEvaluate(c2, "me()")
      c4 = FrameEvaluate(c3, "global text = YDifferenceFromPrevious(w)")
      return c4
    }

    function me()
    {
      global t = String(text)
    }

g(v) This is just an illustration to demonstrate the various features. Much of the script above is redundant, and can be removed. The following two scripts give the same output

    v = AviSource("c:\clip.avi")
    # ScriptClip accepts multi-line scripts:
    Scriptclip(v,"
        text = YDifferenceFromPrevious()
        t = string(text)
        subtitle(t)
    ")

    v = AviSource("c:\clip.avi")
    ScriptClip(v, "Subtitle(String(YDifferenceFromPrevious))")

In the following section some frame dependent info will be written to a text-file.

## Advanced conditional filtering: part II

In the following example, some frame dependent info will be written to a text-file. The first variable “a” indicates whether the frame is combed (for a certain threshold). Note that IsCombed is a filter from the Decomb plugin. The second variable “b” indicates whether there is “much” movement in the frame.

    global sep="."
    global combedthreshold=25

    function IsMoving()
    {
    global b = (diff < 1.0) ? false : true
    }

    function CombingInfo(clip c)
    {
    file = "F:\interlace.log"
    global clip = c
    c = WriteFile(c, file, "a", "sep", "b")
    c = FrameEvaluate(c, "global a = IsCombed(clip, combedthreshold)")
    c = FrameEvaluate(c, "IsMoving")
    c = FrameEvaluate(c, "global diff =
    0.50*YDifferenceFromPrevious(clip) + 0.25*UDifferenceFromPrevious(clip) +
    0.25*VDifferenceFromPrevious(clip)")
    return c
    }

    v = mpeg2source("F:\From_hell\from_hell.d2v").trim(100,124)
    CombingInfo(v)

We can tidy up the two functions, and remove global variables, by writing them as follows:

    function IsMoving(float diff)
    {
     return (diff >= 1.0)
    }

    function CombingInfo(clip c)
    {
     file = "F:\interlace.log"

     c = WriteFile(c, file, "a", "sep", "b")
     c = FrameEvaluate(c,"
           diff = 0.50*YDifferenceFromPrevious() +
           0.25*UDifferenceFromPrevious() + 0.25*VDifferenceFromPrevious()
           b = IsMoving(diff)
           a = IsCombed(combedthreshold)
         ")

     return c
    }

In the following section an example of “adaptive motion/resizing filter” will be considered.

## Advanced conditional filtering: part III

Some adaptive motion/resizing filters appeared on the forums. These filters discriminate between low, medium and high motion in a clip (on frame basis). By doing that, different filters can be used for different kind of motion in the clip. In general, one should use temporal smoothing in low motion scenes, spatial smoothing in high motion scenes and use spatio-temporal smoothing in medium motion scenes.

Below, a simplified version of QUANTIFIED MOTION FILTER v1.5 b1 (10/07/2003) by HomiE FR, is given:

    ----------------------------------------------------
    # QUANTIFIED MOTION FILTER v1.3
    # LOADING AVISYNTH PLUGINS
    LoadPlugin("C:\PROGRA~1\GORDIA~1\mpeg2dec3.dll")
    LoadPlugin("C:\PROGRA~1\GORDIA~1\TemporalCleaner.dll")
    LoadPlugin("C:\PROGRA~1\GORDIA~1\FluxSmooth.dll")
    LoadPlugin("C:\PROGRA~1\GORDIA~1\UnFilter.dll")

    # LOADING QUANTIFIED MOTION FILTER SCRIPT

    Import("E:\temp\QMF\qmf.avs")

    # LOW MOTION FILTER FUNCTION
    # -> SHARP RESIZING + TEMPORAL ONLY
    function Low_Motion_Filter(clip c)
    {
      c = TemporalCleaner(c, 5, 10)
      c = LanczosResize(c, 512, 272)
      return c
    }

    # MEDIUM MOTION FILTER FUNCTION
    # -> NEUTRAL BICUBIC RESIZING + TEMPORAL & SPATIAL
    function Medium_Motion_Filter(clip c)
    {
      c = FluxSmooth(c, 7, 7)
      c = BicubicResize(c, 512, 272, 0.00, 0.50)
      return c
    }

    # HIGH MOTION FILTER FUNCTION
    # -> SOFT RESIZING + SPATIAL ONLY
    function High_Motion_Filter(clip c)
    {
      c = FluxSmooth(c, -1, 14)
      c = UnFilter(c, -30, -30)
      c = BilinearResize(c, 512, 272)
      return c
    }

    # OPENING VIDEO SOURCE
    AviSource("E:\temp\QMF\britney-I_love_rock_'n_roll.avi")
    ConvertToYV12(interlaced=true)
    Telecide(0)

    # APPLYING ADAPTATIVE RESIZING FILTER (USING QMF)
    QMF()
    ----------------------------------------------------

    # QUANTIFIED MOTION FILTER (17/08/2003) by HomiE FR
    (homie.fr@wanadoo.fr)
    # MOTION ESTIMATION FUNCTION
    function ME()
    {
      # SETTING MOTION LEVEL ACCORDING TO AVERAGE DIFFERENCE [1]
      **global motion_level** = (**diff** < threshold_lm) ? 0 :
      motion_level
      **global motion_level** = (**diff** >= threshold_lm && **diff**
      <= threshold_hm) ? 1 : motion_level
      **global motion_level** = (**diff** > threshold_hm) ? 2 :
      motion_level
    }

    # QUANTIFIED MOTION FILTER FUNCTION
    function QMF(clip c, float "threshold_lm", float "threshold_hm", bool
    "debug")
    {
      # SETTING MOTION LEVELS THRESHOLDS [2]
      threshold_lm = default(threshold_lm, 4.0)
      threshold_hm = default(threshold_hm, 12.0)
      global threshold_lm = threshold_lm
      global threshold_hm = threshold_hm

      # ENABLING/DISABLING DEBUG INFORMATION [3]
      debug = default(debug, false)

      # INITIALIZING MOTION LEVEL
      global motion_level = 0

      # SETTING PRESENT CLIP [4]
      global clip = c

      # GETTING OUTPUT RESOLUTION [5]
      width = Width(Low_Motion_Filter(c))
      height = Height(Low_Motion_Filter(c))
      global c_resized = PointResize(c, width, height)

      # APPLYING MOTION FILTER ACCORDING TO MOTION LEVEL [6]
      c = ConditionalFilter(c, Low_Motion_Filter(c), c_resized,
      "**motion_level**", "=", "0")  # [6a]
      c = ConditionalFilter(c, Medium_Motion_Filter(c), c,
      "**motion_level**", "=", "1")       # [6b]
      c = ConditionalFilter(c, High_Motion_Filter(c), c,
      "**motion_level**", "=", "2")         # [6c]

      # PRINTING DEBUG INFORMATION [7]
      c = (debug == true) ? ScriptClip(c, "Debug()") : c

      # GETTING MOTION LEVEL THROUGH MOTION ESTIMATION [8]
      c = FrameEvaluate(c, "ME()")

      # GETTING DIFFERENCES BETWEEN PAST/PRESENT FRAMES [9]
      c = FrameEvaluate(c, "**global diff** =
      0.50*YDifferenceFromPrevious(clip) + 0.25*UDifferenceFromPrevious(clip)
      + 0.25*VDifferenceFromPrevious(clip)")
      return c
    }

    # DEBUG INFORMATION FUNCTION
    function Debug(clip c)
    {
      # PRINTING VERSION INFORMATION [10]
      c = Subtitle(c, "Quantified Motion Filter", x=20, y=30,
      font="lucida console", size=18, text_color=$FFFFFF)
      c = Subtitle(c, "by HomiE FR (homie.fr@wanadoo.fr)", x=20, y=45,
      font="lucida console", size=14, text_color=$FFFFFF)

      # PRINTING MOTION ESTIMATION INFORMATION [11]
      c = Subtitle(c, "motion estimation", x=20, y=85, font="lucida
      console", size=18, text_color=$FFFFFF)
      c = Subtitle(c, "diff = "+string(**diff**), x=20,y=110,
      font="lucida console", size=16, text_color=$FFCCCC)

      # PRINTING QUANTIFIED MOTION FILTER INFORMATION [12]
      c = Subtitle(c, "quantified motion filter", x=20, y=135,
      font="lucida console", size=18, text_color=$FFFFFF)
      c = (**motion_level** == 0) ? Subtitle(c, "scene type = low
      motion", x=20, y=160, font="lucida console", size=16,
      text_color=$66FF66) : c
      c = (**motion_level** == 1) ? Subtitle(c, "scene type = medium
      motion", x=20, y=160, font="lucida console", size=16,
      text_color=$66FF66) : c
      c = (**motion_level** == 2) ? Subtitle(c, "scene type = high
      motion", x=20, y=160, font="lucida console", size=16,
      text_color=$66FF66) : c
      return c
    }
    ----------------------------------------------------

This filter chain works like this:

- When Vdub requests a frame, AviSynth requests a frame from QMF.
- QMF request a frame from FrameEvaluate [9].
- After doing this the script [9] is evaluated, and the global variable diff is assigned after requesting a frame from AviSource. FrameEvaluate [9] requests a frame from FrameEvaluate [8].
- Once again the script [8] is evaluated:
- when evaluating me(), the global variable motion_level is assigned for that frame [1]
- If debug=true, a frame is requested from ScriptClip [7], and thus from Debug().
- After that (and also when debug was set to false) a frame is requested from the last ConditionalFilter [6c], which requests a frame from [6b], which in turn requests a frame from [6a].
- Note that in the end, a frame of High_Motion_filter, Medium_Motion_filter, or Low_Motion_filter is requested depending on the value of motion_level.
- QMF request a frame from Telecide, Telecide from ConvertToYV12 and finally ConvertToYV12 from AviSource.
- AviSource produces the frame and sends it to ConvertToYV12, etc.

A few details were omitted, but this is how the script basically works.

$Date: 2012/04/09 08:19:32 $