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| Main Page | General Info | Loading Clips | Loading Scripts | Common Error Messages | Processing Different Content | Dealing with YV12 | Processing with Virtualdub Plugins |


What is AviSynth?

AviSynth (AVI SYNTHesizer) is a frameserver. An excellent description is given on Lukes homepage:

"AviSynth is a very useful utility created by Ben Rudiak-Gould. It provides many options for joining and filtering videos. What makes AviSynth unique is the fact that it is not a stand-alone program that produces output files. Instead, AviSynth acts as the "middle man" between your videos and video applications.

Basically, AviSynth works like this: First, you create a simple text document with special commands, called a script. These commands make references to one or more videos and the filters you wish to run on them. Then, you run a video application, such as Virtualdub, and open the script file. This is when AviSynth takes action. It opens the videos you referenced in the script, runs the specified filters, and feeds the output to video application. The application, however, is not aware that AviSynth is working in the background. Instead, the application thinks that it is directly opening a filtered AVI file that resides on your hard drive.

There are five main reasons why you would want to use AviSynth:

  1. Join Videos: AviSynth lets you join together any number of videos, including segmented AVIs. You can even selectively join certain portions of a video or dub soundtracks.
  2. Filter Videos: Many video processing filters are built in to AviSynth. For example, filters for resizing, cropping, and sharpening your videos.
  3. Break the 2 GB Barrier: AviSynth feeds a video to a program rather than letting the program directly open the video itself. Because of this, you can usually use AviSynth to open files larger than 2 GB in programs that don't natively support files of that size.
  4. Open Unsupported Formats: AviSynth can open almost any type of video, including MPEGs and certain Quicktime MOVs. However, when AviSynth feeds video to a program, it looks just like a standard AVI to that program. This allows you to open certain video formats in programs that normally wouldn't support them.
  5. Save Disk Space: AviSynth generates the video that it feeds to a program on the fly. Therefore, no temporary or intermediate videos are created. Because of this, you save disk space."

Who is developing AviSynth?

Originally AviSynth (up to v1.0b) was developed by Ben Rudiak-Gould mirror of his homepage. Currently it is developed by IanB and others.

Where can I download the latest versions of AviSynth?

The most recent stable version is v2.6.0, which can be found here.

What are the main bugs in these versions?

Current bugs can be found in the documentation on the AviSynth project page. Fixed bugs can be found in the Changelist.

Where can I find documentation about AviSynth?

Documentation about the filters of AviSynth can be found on this site Main Page, and in particular here: Internal filters. You should read these documents before posting to the forum, but it's OK to post if you have trouble understanding them.

How do I install/uninstall AviSynth?

Starting from v2.06 AviSynth comes with an auto installer. Also make sure you have no other versions of AviSynth floating around on your harddisk, because there is a chance that one of those versions will be registered. Remove them if necessary. For uninstalling AviSynth go to "program", "AviSynth 2" and select "Uninstall AviSynth".

Installing AviSynth v2.05 or older versions: move avisynth.dll to your system/system32 directory and run install.reg. For uninstalling run uninstall.reg and delete avisynth.dll.

What is the main difference between v1.0x, v2.0x, v2.5x and v2.6x?

The versions v1.0x and v2.0x are compatible and outdated. The main difference with v2.5x is that the internal structure of AviSynth has changed (YV12 and multichannel support) with the consequence that external plugins compiled for v1.0x/v2.0x will not work for v2.5x/v2.6x and vice versa. In v2.6x other planar formats like YV16, YV24 and Y8 are added. v2.5x plugins will work in v2.6x but not vice-versa.

How do I make an AVS-file?

Use your preferred text editor (e.g. Notepad). See also this.

Although AviSynth doesn't need them, there are several GUIs (graphical user interface) which may help you writing your AVS files. You can read a description for each one of them here.

Where do I save my AVS-file?

Anywhere on your drives. But if you're using relative paths to source files, you might want to put your AVS-file close to your source files.

How do I know which version number of AviSynth I have?

Open a text-editor, for example notepad. Add the following line


and save the file with the extension "avs". Save for example as "version.avs" (make sure that the extension is "avs" and not "txt"). Open the file in an application which can read AVI-files, for example WMP 6.4 or Media Player Classic. The version number will be displayed.

Are plugins compiled for v2.5x/v2.6x compatible with v1.0x/v2.0x and vice versa?

As explained here that is not the case. However it is possible to use a v1.0x/v2.0x plugin in v2.5x/v2.6x, as explained here.

How do I use a plugin compiled for v2.0x in v2.5x/2.6?

In the WarpSharp Package you will find a plugin called "LoadPluginEx.dll". When using an older version of LoadPluginEx.dll, don't move this plugin to your plugin folder. But move it to a separate directory, otherwise VirtualDubMod and WMP6.4 will crash on exit. This will enable you using v2.0x plugins in v2.5x. An example script (using the v2.0x plugin Dust by Steady):

LoadPlugin("C:\Program Files\avisynth2_temp\plugins\LoadPluginEx.dll")
LoadPlugin("C:\Program Files\avisynth2_temp\plugins\dustv5.dll")


If you want to automate this process, have a look at LoadOldPlugins.

How do I switch between different AviSynth versions without re-install?


  • You can use AvisynthSwitcher available here. Versions v2.08 and v2.50 are provided, but you can easily add a new one under AvisynthSwitcher\versions\Avisynth 2.x.x. Discussion
  • Some other ways are described here.

VirtualdubMod, WMP6.4, CCE and other programs crash every time on exit (when previewing an avs file)?

This problem can be caused by certain plugins in your (autoloading) plugin folder. The solution is to move the problematic plugins outside your plugin folder and load them manually.

My computer seems to crash at random during a second pass in any encoder?

AviSynth is highly optimized. As a consequence it is possible that your computer seems to crash at random during a second pass. Try running the Prime95 stress test for an hour, to check if your system is stable. If this test fails (or your computer locks up) make sure that your computer is not overclocked and lower your bus speed of your processor in steps of (say) five MHz till the crashes are gone.

Is there a command line utility for encoding to DivX/XviD using AviSynth?

  • There is a command line utility called [1] (and AVS2AVI GUI) for encoding to DivX / XviD using AviSynth (discussion).

Does AviSynth have a GUI (graphical user interface)?

AviSynth doesn't have a full fledged gui, but several tools are available:

  • VirtualDubMod: The following AviSynth related utilities are present:
    • 'Open via AVISynth' command: This allows you to open any AviSynth compatible video file by automatically generating a suitable script by a selectable template.
    • AVS Editor (Hotkey Ctrl+E): Just open your AVS and under tools select "script editor". Change something and press F5 to preview the video.
  • AvisynthEditor: This is an advanced AviSynth script editor featuring syntax highlighting, auto-complete code and per version plugin definition files. Here is a screenshot. It can be found here. Discussion can be found on Doom9.org forum.
  • AVSGenie: AVSGenie allows the user to select a filter from a drop down list or from a popup menu. An editable page of parameters will then be brought into view, with a guide to the filter and it's parameters. A video preview window opens, showing "source" and "target" views. The source window, in simple cases, shows output of the first line of the script, generally an opened video file. The target window shows the output of the whole script. In this way, effects of filters can easily be seen. The line which represents the source window can be changed. Discussion can be found here.
  • AvsP: It's a tabbed script editor for Avisynth. It has many features common to programming editors, such as syntax highlighting, autocompletion, call tips. It also has an integrated video preview, which when coupled with tabs for each script make video comparisons a snap. What really makes AvsP unique is the ability to create graphical sliders and other elements for any filter's arguments, essentially giving AviSynth a gui without losing any of its powerful features.Discussion can be found here

| Main Page | General Info | Loading Clips | Loading Scripts | Common Error Messages | Processing Different Content | Dealing with YV12 | Processing with Virtualdub Plugins |

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