## AviSynth Syntax - Control functions

They facilitate flow of control (loading of scripts, arguments checks, global settings adjustment, etc.).

- Apply | | Apply(string func_string [, arg1 [, arg2 [, ... [, argn]]]] )

  Apply calls the function or filter func_string with arguments arg1, arg2, ..., argn (as many as supplied). Thus, it provides a way to call a function or filter by name providing arguments in the usual way as in a typical function call.
  Consequently, `Apply("f", x)` is equivalent to `f(x)` which in turn is equivalent to `Eval("f(" + String(x) + ")")`.
  Examples:

    # here the same call to BicubicResize as in the Eval() example is shown
    Apply("BicubicResize", last, 352, 288)
    # Note that the clip argument must be supplied - 'last' is not implicitly assumed

- Eval | | Eval(expression [, string "name"])

  Eval evaluates an arbitrary expression as if it was placed inside the script at the point of the call to Eval and returns the result of evaluation (either to the variable that is explicitly assigned to or to the last special variable.
  You can use Eval to construct and evaluate expressions dynamically inside your scripts, based on variable input data. Below some specific examples are shown but you get the general idea.
  Argument name is filename specified in the error message instead of script name.
  Examples:

    # this calls BicubicResize(last, 352, 288)
    settings = "352, 288"
    Eval( "BicubicResize(" + settings + ")" )
    ...
    # this will result in Defined(u) == false
    u = Eval("#")
    ...
    # this increments a global based on a variable's value
    dummy = Eval("global my_counter = my_counter + " + String(increment))

- Import | | Import(filename)

  Import evaluates the contents of another AviSynth script and returns the imported script's return value. Typically it is used to make available to the calling script library functions and the return value is not used. However this is simply a convention; it is not enforced by the AviSynth Syntax. See also the dedicated Import page in Internal filters for other possible uses.
  Possible scenarios (an indicative list) where the return value could be of use is for the library script to:
  - indicate whether it succesfully initialised itself (a bool return value),
  - inform for the number of presets found on disk (an int return value);
  the value then could be tested by the calling script to decide what action to take next.
  Examples:

    Import("mylib.avsi")  # here we do not care about the value (mylib.avsi contains only functions)
    ...
    okflag = Import("mysources.avsi")  # mysources loads predetermined filenames from a folder into globals
    source = okflag ? global1 + global2 + global3 : BlankClip()

- Select | | Select(index, item0 [, item1 [, ... [, itemn]]])

  Returns the item selected by the index argument, which must be of int type (0 returns item0, 1 returns item1, ..., etc). Items can be any script variable or expression of any type and can even be mixed.
  Examples:

    # select a clip-brush from a set of presets
    idx = 2
    brush = Select(idx, \
         AviSource("round.avi"), \
         rectangle, \
         diagonal, \
         diagonal.FlipHorizontal)

- Default | | Default(x, d)

  Returns x if Defined(x) is true, d otherwise. x must either be a function's argument or an already declared script variable (ie a variable which has been assigned a value) else an error will occur.
  Examples:

    function myfunc(clip c, ..., int "strength") {
        ...
        strength = Default(strength, 4) # if not supplied make it 4
        ...
    }

- Assert | | Assert(condition [, err_msg])

  Does nothing if condition is true; throws an error, immediately terminating script execution, if condition is false. In the later case err_msg, if supplied, is presented to the user; else the standard message "Assert: assertion failed". shows up.
  Examples:

    function myfunc(clip c, ..., int "strength") {
        ...
        strength = Default(strength, 4) # if not supplied make it 4
        Assert(strength > 0, "'strength' must be positive")
        ...
    }

- NOP | | NOP()

  This is a no-operation function provided mainly for conditional execution with non-return value items such as Import, when no "else" condition is desired. That is, use it whenever the AviSynth Syntax requires an operation (such as with the ?: operator) but your script does not need one.
  Return value: 0 (int type).
  Examples:

    preset = want_presets ? AviSource("c:\presets\any.avi") : NOP
    ...
    loadlib ? Import("my_useful_functions.avs") : NOP

- UnDefined | v2.60 | UnDefined()
    Returns the undefined state.
    It's the state for which Defined() returns false.
    Examples:

      x = Undefined()
      Defined(x) # = true

- SetMemoryMax | v2 | SetMemoryMax(amount)

  Sets the maximum memory (in MB) that AviSynth uses for its internal Video Frame cache to the value of amount. From v2.5.8, setting to zero just returns the current Memory Max value. In the 2.5 series the default Memory Max value is 25% of the free physical memory, with a minimum of 16MB.
  From rev 2.5.8 RC4, the default Memory Max is also limited to 512MB.

  Free | <64 | 128 | 256 | 512 | 1024 | 2048 | 3072
  Default Max v2.57 and older | 16 | 32 | 64 | 128 | 256 | 512 | 768
  Default Max since v2.58 RC4 | 16 | 32 | 64 | 128 | 256 | 512 | 512

  In some versions there is a default setting of 5MB, which is quite low. If you encounter problems (e.g. low speed) try to set this values to at least 32MB. Too high values can result in crashes because of 2GB address space limit.
  Return value: Actual MemoryMax value set.
  Examples:

    SetMemoryMax(128)

- SetWorkingDir | v2 | SetWorkingDir(path)

  Sets the default directory for AviSynth to the path argument.
  This is primarily for easy loading of source clips, importing scripts, etc. It does not affect plugins' autoloading.
  Return value is 0 if successful, -1 otherwise.
  Examples:

    SetWorkingDir("c:\my_presets")
    AviSource("border_mask.avi")  # this loads c:\my_presets\border_mask.avi

- SetPlanarLegacyAlignment | v2.56 | SetPlanarLegacyAlignment(mode)

  Set alignment mode for planar frames. mode can either be true or false.
  Some older plugins illegally assume the layout of video frames in memory. This special filter forces the memory layout of planar frames to be compatible with prior versions of AviSynth. The filter works on the GetFrame() call stack, so it effects filters before it in the script.
  Examples:

    Example : Using an older version of Mpeg2Source() (1.10 or older):

    LoadPlugin("...\Mpeg2Decode.dll")
    Mpeg2Source("test.d2v")         # A plugin that illegally assumes the layout of memory
    SetPlanarLegacyAlignment(true)  # Set legacy memory alignment for prior statements
    ConvertToYUY2()     # Statements through to the end of the script have
    ...                             # advanced memory alignment.

- OPT_AllowFloatAudio | v2.57 | global OPT_AllowFloatAudio = True

  This option enables WAVE_FORMAT_IEEE_FLOAT audio output. The default is to autoconvert Float audio to 16 bit.

- OPT_UseWaveExtensible | v2.58 | global OPT_UseWaveExtensible = True

  This option enables WAVE_FORMAT_EXTENSIBLE audio output. The default is WAVE_FORMAT_EX.
  Note: The default DirectShow component for .AVS files, "AVI/WAV File Source", does not correctly implement WAVE_FORMAT_EXTENSIBLE processing, so many application may not be able to detect the audio track. There are third party DirectShow readers that do work correctly. Intermediate work files written using the AVIFile interface for later DirectShow processing will work correctly if they use the DirectShow "File Source (async)" component or equivalent.

- OPT_VDubPlanarHack | v2.60 | global OPT_VDubPlanarHack = True

  This option enables flipped YV24 and YV16 chroma planes. This is an hack for early versions of Virtualdub with YV24/YV16 support.

- OPT_dwChannelMask | v2.60 | global OPT_dwChannelMask(int v)

  This option enables you to set ChannelMask. It overrides WAVEFORMATEXTENSIBLE.dwChannelMask which is set according to this table
  0x00004, // 1 -- -- Cf
  0x00003, // 2 Lf Rf
  0x00007, // 3 Lf Rf Cf
  0x00033, // 4 Lf Rf -- -- Lr Rr
  0x00037, // 5 Lf Rf Cf -- Lr Rr
  0x0003F, // 5.1 Lf Rf Cf Sw Lr Rr
  0x0013F, // 6.1 Lf Rf Cf Sw Lr Rr -- -- Cr
  0x0063F, // 7.1 Lf Rf Cf Sw Lr Rr -- -- -- Ls Rs

- OPT_AVIPadScanlines | v2.60 | global OPT_AVIPadScanlines = True

  This option enables DWORD aligned planar padding. Default is packed aligned planar padding. See memory alignment used in the AVIFile output emulation.

Back to Internal functions.

`$Date: 2012/04/15 14:13:14 $`