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What is AviSynth?

• It’s a powerful tool for video post-production.
• It’s a frameserver, providing instant transfer to other video applications without the need for temporary files.
• It’s a script system for non-linear editing and video filters and effects.

AviSynth itself does not provide a graphical user interface (GUI). While scripting may at first seem tedious and unintuitive, it 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. You have complete control of everything.

The scripting language is simple yet powerful – basic filters can be combined to create useful and unique effects. It is easy to create a quick script to solve some video problem. It can do much more than that, though: to get an idea, take a quick glance at all the third-party plugins available, or browse the doom9 forum to see what AviSynth users and developers are getting up to lately!

AviSynth takes its name from AVI, a digital media format, and Synthesis, because it creates (synthesizes) a virtual (in memory, not on disk) media file – “generating video and audio data according to the script and feeding it to the application as needed.” (in the words of its inventor, Ben Rudiak-Gould). It could be used as a Video Synthesizer, but this is not its usual function.

AviSynth is free open-source software, under the GNU General Public License GPLv2; see Copyrights.

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 explaing the basics, tips on specific conversion types and common tasks. Troubleshooting your scripts and configuration.	Download AviSynth Official builds v.2.6.0 ST, 32-bit at SourceForge Unofficial builds v.2.6.0 MT, 32-bit, author SET at forum.doom9.org Forks AviSynth+, 32-bit and 64-bit, author ultim at forum.doom9.org. Download: avs-plus.net | Wiki page: AviSynth+ AvxSynth: a Linux port of AviSynth AvxSynth is a native port of AviSynth 2.5.8 running on Ubuntu 32/64. Deprecated 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 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.	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 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).