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With these functions you can add external filters (DLLs) to the AviSynth script environment.


[edit] LoadPlugin

Loads one or more standard (C++) AviSynth plugins.

LoadPlugin(string filename [, string filename...])

string  filename =
The path of the .DLL file(s).

[edit] LoadCPlugin

Loads so-called AviSynth C-plugins. C-plugins are created in pure C (unlike most Avisynth plugins, which are created with MS C++), use a special C API, and must be loaded with LoadCPlugin.

LoadCPlugin(string filename)
LoadCPlugin(string filename [, string filename...]) AVS+
Load_Stdcall_Plugin(string filename)
Load_Stdcall_Plugin(string filename [, string filename...]) AVS+

string  filename =
The path of the .DLL file(s).
  • The plugin's documentation should advise you if LoadCPlugin is needed.
  • Load_Stdcall_Plugin is merely an alias or alternate name.
  • Advice: keep these plugins outside your autoload directory to prevent crashes.

[edit] LoadVirtualDubPlugin

Loads a plugin written for VirtualDub. These are distributed as special DLLs with the file extension .VDF.

LoadVirtualDubPlugin (string filename, string filtername [, int preroll])

string  filename =
The path of the .VDF file.
string  filtername =
The name to be given to the plugin function after loading in AviSynth.
int  preroll = 0
Some filters' output depends on previous frames; for these, preroll should be set to a suitable number.

Note that there is a new parameter but _not_ for use in LoadVirtualdubPlugin, but when calling the loaded VDF filter from the script.

AVS+string  rangehint = ""
This extra filter parameter added at the end of filter's (unnamed) parameter list: string rangehint.
The imported Virtualdub filters (of course which are supporting the extra feature) are getting and extra named parameter to the end.
This parameter can tell the filter about a YUV-type clip colorspace info
Allowed values:
  • "rec601": limited range + 601
  • "rec709": limited range + 709
  • "PC.601": full range + 601
  • "PC.709": full range + 709
  • ""  : not defined (same as not given)
Parameter will be ignored when clip is non-YUV
How it works: the hint will _not_ change the internal VirtualDub colorspace constant (e.g. kPixFormat_YUV420_Planar -> kPixFormat_YUV420_Planar_709 will not happen).
Instead the base color space is kept and colorSpaceMode and colorRangeMode will set in PixmapLayout.formatEx.
Filter can either use this information or not, depending on supported API version and its implementation.
E.g. Crossfade(20,30) -> Crossfade(20,30,"rec601") (a bit stupid example, just for showing the syntax because this specific filter won't use it).
  • Supported color spaces and features:
  • VirtualDub filters originally support only RGB32.
  • AVS+ Since Avisynth+ r2724 LoadVirtualdubPlugin was updated to support newer interface versions.
This update changed the supported interface version from V6 to V20, and Filtermod version 6 (partial support)
Supported extras:
VirtualDub2 support with extended colorspaces
  • Allow RGB24, RGB48, RGB64 besides RGB32
  • RGBP/RGBAP 8 bit: since this format is not supported directly by Virtualdub filters, LoadVirtualdubPlugin automatically converts 8 bit Planar RGB to/from RGB24, RGBAP to/from RGB32 (lossless)
  • RGB48/RGBP16/RGBAP16: since this format is not supported directly by Virtualdub filters, LoadVirtualdubPlugin automatically converts them to/from RGB64 (lossless)
  • YUV(A) 8 bits: YV12, YV16, YV24, YV411, YUVA420P8, YUVA422P8, YUVA444P8
  • YUV(A) 10-16 bits (properly set "ref_x" maximum levels, no autoconvert)
  • Supports prefetchProc2 callback (API >= V14 and prefetchProc2 is defined) for multiple input frames from one input clip
  • PrefetchFrameDirect and PrefetchFrame are supported. PrefetchFrameSymbolic not supported
  • Supports prefetchProc callback (API >= V12 and prefetchProc is defined)
  • Supports when filter changes frame count of the output clip
  • Supports specifying some colorspace properties. See rangehint

[edit] LoadVFAPIPlugin

Loads VFAPI plugins (eg, QTReader, TMPGEnc). These are distributed as special DLLs with the file extension .VFP.

LoadVFAPIPlugin (string filename, string filtername)

string  filename =
The path of the .VFP file.
string  filtername =
The name to be given to the plugin function after loading in AviSynth.

[edit] Plugin Autoload and Name Precedence

It is possible to put all plugins and script files with user-defined functions or (global) variables in an autoload directory, from which all files with the extension .AVSI and .DLL are loaded at startup, then unloaded and reloaded dynamically as the script needs them.

.AVSI scripts in this directory should only contain function definitions and global variables; they should not have a main processing section (else strange errors may occur). It also is not recommended to put other files in that directory.

The directory is stored in the registry. You can use double-clicking a .REG-file with the following lines to set the path (of course inserting your actual path):


"plugindir2_5"="c:\\program files\\avisynth 2.5\\plugins"

The order in which function names take precedence is as follows:

  1. User-defined function (always have the highest priority)
  2. Plugin (external) function (higher priority than built-in)
  3. Built-in (internal) function

Inside those groups the function loaded last takes precedence; there is no error in a namespace conflict.
It follows that there is no harm in loading the same plugin more than once.[dubious – discuss]

[edit] Plugin Autoload and Conflicting Function Names

A problem that may arise when multiple plugins have functions with the same name. You won't know which function will be called in your script, as this will depend on loading order. To call a particular function in this situation, AviSynth's DLLName_function() feature automatically creates prefix aliases; so for example, foo.dll's bar() function may be called as foo_bar(). This works both for auto-loaded plugins and for plugins loaded with LoadPlugin.

Suppose you have the plugins mpeg2dec.dll and mpeg2dec3.dll in your autoload directory; if you call


you won't know which plugin will be used in your script, as both have an mpeg2source function.

To load the file with mpeg2dec.dll (which outputs YUY2), call


or to load the file with mpeg2dec3.dll (which outputs YV12), call


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