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What is AviSynth?

AviSynth is a powerful tool for video post-production. It provides ways of editing and processing videos. AviSynth works as a frameserver, providing instant editing without the need for temporary files. AviSynth itself does not provide a graphical user interface (GUI), but instead relies on a script system that allows advanced non-linear editing. While this may at first seem tedious and unintuitive, it is remarkably powerful and is a very good way to manage projects in a precise, consistent, and reproducible manner. Because text-based scripts are human readable, projects are inherently self-documenting. The scripting language is simple yet powerful, and complex filters can be created from basic operations to develop a sophisticated palette of useful and unique effects.

AviSynth is free open-source software, and licensed under the GNU General Public License GPLv2.

New to AviSynth – Start Here

• Your first script – A guide for total newbies.
• Getting started – An introductory guide.
• Grammar – An introduction to the AviSynth scripting language.
• Filter introduction – An introductory guide to most common AviSynth filters.
• Script examples – Putting everything together in the real world.
• AviSynth FAQ – Answers to many common problems.
• More information (How does it work? When is it useful? Why no GUI? What applications work well with AviSynth?)
• Guides – Guides explaining the basics, tips on specific conversion types and common tasks.
• Troubleshooting your scripts and configuration.

Download AviSynth

• Current Builds

AviSynth+

New features, backward compatible, native support for Unix-like OSes.

Wiki page

Homepage (avs-plus.net) 

Latest release (GitHub) 

Discussion at forum.doom9.org

• Deprecated Official builds

v.2.6.0 ST, 32-bit at SourceForge

• Deprecated Unofficial builds

v.2.6.0 MT, 32-bit, author SET
at forum.doom9.org

• Universal Installer

Install—and quickly switch between—AviSynth versions:

• Avisynth 2.5.8, 2.6.0, 2.6.0 MT, 2.6.1 Alpha
• Avisynth+ 32-bit, 64-bit

Get it here at forum.doom9.org

• Deprecated Multithread Version

v.2.5.8 MT, 32-bit, author SET,
discussion at forum.doom9.org

v.2.5.8 MT, 64-bit, author SET,
compiled by JoshyD at forum.doom9.org

AvxSynth
AviSynth 2.5.8 running on Ubuntu 32/64.

• Old Bugs and issues

Known Issues in v2.58.

Known Issues in v2.60.

Script Syntax

The official reference documentation.

• AviSynth Syntax overview
  • Script variables – How to declare and use them in scripts.
  • Operators – Available operators and relative precedence.
  • Internal functions – General purpose functions for math, logic etc.
  • Clip properties – Properties such as Width, Height, Framerate etc.
  • Control structures – Language constructs for script flow control.
  • User defined script functions – How to define and use them in scripts.
  • Plugins – How to load them (AviSynth, VirtualDub, VFAPI and C-plugins); autoloading and name-precedence explained. Most External filters are plugins; the rest are regular scripts.
  • Runtime environment – Scripting on a per-clip frame basis.
  • Function objects – AVS+user defined functions as variables, capture external variables, use them in ScriptClip instead of stringified script fragments.

Filters and Utilities

• Internal filters – Included media filters, organized by category.
• External filters – Hundreds of separately downloadable filters, organized by category.
• User pages hosted on this site:
  • AviSynth Filter Collection – Warpenterprises
  • Fizick’s AviSynth plugins
  • vcmohan’s Plugin Filters
  • stickboy’s AviSynth Stuff
• Shared functions – Commonly used script functions.
• Utilities – A list of GUIs, command-line, batch and other AviSynth related utilities.

Scripting reference

Beyond scripting basics

• Scripting reference overview
  • The full AviSynth grammar – The AviSynth grammar revisited and explained in detail.
  • The script execution model – The steps behind the scenes from the script to the final video clip output. The filter graph. Scope and lifetime of variables. Evaluation of runtime scripts.
  • User functions – How to effectively write and invoke user defined script functions; common pitfalls to avoid; ways to organise your function collection and create libraries of functions, and many more.
  • Block statements – Techniques and coding idioms for creating blocks of AviSynth script statements.
  • Arrays – Using arrays (and array operators) for manipulating collections of data in a single step.
  • Scripting at runtime – How to unravel the power of runtime filters and create complex runtime scripts that can perform interesting (and memory/speed efficient) editing/processing operations and effects.

Advanced topics

• Advanced Scripting Tips – Using recursion, weaving 3 clips, and other programming tips.
• Advanced topics – Chroma Upsampling Error, color conversions, hybrid video, motion compensation, and other advanced subjects.
• Aspect ratios explained – Introduction to aspect ratios (DAR, PAR, SAR), and how to use that for resizing your clip.
• High bit-depth (Deep Color) support with AviSynth

Development

• Want to get involved?
• The official project.
• Learn how to install compilers and setup environments.
• Learn how to compile AviSynth, AviSynth plugins and console applications that access AviSynth.
• Learn how to debug AviSynth, AviSynth plugins and console applications that access AviSynth.
• Filter SDK – AviSynth plugin programming tips.
• Avisynth Plugin Development in C – A tutorial to write a plugin with C.
• AviSynth Developer Forum
• The ongoing changelist.
• About the development of AviSynth v3 (which will be platform independent).
• References to image processing algorithms.

About This Website

We need your help to build and improve our site!

• Editing is easy! Please see Editing pages and Formatting.
• To port this site to another language, please see the MediaWiki Localisation Guide.
• Filter and script authors – please see Submit your Documentation on doom9.org, and the documentation template ExampleFilter.

Documentation Copyright

AviSynth documentation is Copyright (c) 2002-2025 AviSynth developers and contributors.

The contents of avisynth.org and avisynth.nl are released under the Creative Commons Attribution-ShareAlike 3.0 License (CC BY-SA 3.0).