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» AboutAviSynth



Section 1: About AviSynth

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Q1.1: What is AviSynth ?

A: AviSynth (AVI SYNTHesizer) is a frameserver. An excellent discription 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."

Q1.2: Who is developing AviSynth ?

A: AviSynth (up to v1.0b) was developed by Ben Rudiak-Gould, of whom we have currently no homepage. Ben stopped developing and Edwin van Eggelen continued, see [1]. His latest release is version v1.0b6 which can be found on Edwins homepage given above.

Some versions appeared on the AviSynth forum, for example [v1.0b7a by Divine] and [v1.0b7d by Dividee].

In the beginning of July 2002 there was a second revision of the sourceforge project. (In the [first sourceforge project] didn't happen much.) The most recent version is [v2.54], but more recent weekly builds can be found [here]. For documentation have a look at Q1.5).

Q1.3: Where can I download the latest versions of AviSynth ?

A: See Q1.2. It is also contained in the DVD2SVCD package and on the download page of Doom (these might be not be the newest versions of AviSynth).

Q1.4: What are the main bugs in these versions ?

A: The most recent versions:

v2.01: ?

v2.02: Layer and MergeChroma don't work.

v2.05: Loop doesn't work when loading a clip without sound.

v2.06/v2.07/v2.50: SegmentedAviSource doesn't load the avi's if the last empty segment isn't deleted.

v2.50 beta; AviSynthTwoFiveZeroBugs.

v2.51 beta; AviSynthTwoFiveOneBugs.

v2.52 AviSynthTwoFiveTwoBugs.

other bugs can be found in the documentation on the project page, see Q1.5.

Q1.5: Where can I find documentation about AviSynth ?

A: Documentation about the filters of AviSynth can be found on this site http://www.avisynth.org/, and in particular at one of the [links]. For a tutorial on avisynth scripting, have a look at the [project page]. You should read these documents before posting to the forum (but it's OK to post if you have trouble understanding them).

Q1.6: How do I install/uninstall AviSynth ?

A: In v2.05 or older versions: move avisynth.dll to your system/system32 directory and run install.reg. Starting from v2.06 AviSynth comes with an auto installer. Also make sure you have no other versions of AviSynth floating around on your harddisc, 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".

Q1.7: Is there any difference between v1.0x, v2.0x or v2.5x ?

A: The versions v1.0x and v2.0x are compatible (the main difference is that v2.0x doesn't contain IPCSource, while it contains other filters which are not present in v1.0x). 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 or v2.0x will not work for v2.5x and vice versa.

Q1.8: Are plugins compiled for v2.5x compatible with v1.0x/v2.0x and vice versa ?

A: As explained in Q1.7 that is not the case. However it is possible to use a v1.0x/v2.0x plugin in v2.5x, see Q1.15.

Q1.9: Which encoding programs support YV12 ?

A: The regular builds of Virtualdub (till v1.5.4) have no internal YV12 support. There are two options for encoding to DivX/XviD:

  1. There is a modified version (called VirtualdubMod) which has YV12 support: This modification (by pulco-citron, Suiryc and Belgabor) has OGM and AVS-preview support. It can be downloaded from [here]. In order to use the YV12 support (without doing any color conversions) you have to load your AVI in VirtualdubMod and select "fast recompress".
  2. For easy (and fast) YV12 support, you can also try out the new commandline compressor: AVS2AVI, see also Q1.21.

Q1.10: How do I use v2.5x if the encoding programs can't handle YV12 (like Virtualdub, TMPGEnc or CCE SP) ?

A: Using Virtualdub you have to add "ConvertToYUY2" to your script or you have to install a YV12 decompressor like DivX5 or one of the recent XviD builds of Koepi (XviD-04112002-1 or newer). Enabling "fast recompress" implies that there will be a YV12 -> YUY2 -> YV12 conversion. ( DivX3/4 also supports YV12, except that PIV users could experience crashes when encoding to DivX4 in YV12. )

Using TMPGEnc you have to add the line ConvertToRGB24 to your script, and for CCE SP you need to add the line ConvertToYUY2 to your script, since Windows has no internal YV12 compressor. You can also install DivX5 or one of the recent XviD builds of Koepi [XviD-04112002-1 or newer] which will decompress the YV12-AVI for you when loading the avi in TMPGEnc or CCE SP.

Q1.11: How do I use with AviSynth v2.5 with Gordian Knot?


- If you are using GKnot 0.26 you have to rename mpeg2dec3.dll (the one for AviSynth v2.5) to mpeg2dec.dll, and virtualdubmod.exe to virtualdub.exe (keeping copies of the original exe and dll somewhere).

- If you are using GKnot 0.27 you can follow the same procedure as above, or you can enter mpeg2dec3.dll as an alternative mpeg2dec.dll in the options menu and rename virtualdubmod.exe to virtualdub.exe.

- But you can also try the new GKnot 0.28.

If you are using VirtualdubMod or older and experience problems, download the latest [prerelease].

Q1.12: What are the main advantages and processing/encoding in YV12?

A: There are two advantages:

  1. speed increase:
    It depends entirely on the external plugins whether they will have YV12 support or not. If they have then speed increases like 25-35 percent are expected. Of course there will only be a large speed increase if both your source and target are in YV12, for example in DVD to DivX / XviD conversions.
  2. no color conversions:
    The color information doesn't get interpolated (so often) and thus stays more realistic. Even if you have to do color conversions (because your are encoding with CCE SP or TMPGEnc) you have the advantage that putting off the YV12->YUY2 (or RGB24 for TMPGEnc) conversion until the end of the script allows you to first IVTC or Deinterlace to create progressive frames. But the YV12 to YUY2 conversion for progressive frames maintains more chroma detail than it does for interlaced or field based frames.

Q1.13: Is there a command line utility for encoding to DivX/XviD using AviSynth ?

A: As explained in Q1.9 there is a command line utility called [AVS2AVI] (and AVS2AVI GUI]) for encoding to DivX / XviD using AviSynth.

Q1.14: Where can I find VCF2AVS ?

A: VCF2AVS is a nice litte tool to convert vcf to avs files. You can edit your captures in vdub (basically cutting, cropping and resizing), then edit the resulting avs. Be carefull since there are two versions floating around:

  • VCF2AVS by Darksoul71 which can be found [here]
  • VCF2AVS by BB (more basic) which can be found [here]

Try them both and look which one fullfills your needs :)

Q1.15: How do I use a plugin compiled for v2.0x in v2.5x ?

A: In WarpSharp-package for AviSynth v2.5x you will find a plugin called "LoadPluginEx.dll". When using an older version of LoadPluginEx.dll, don't move this plugin to your plugin dir. But move it to a separate dir, 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.

Q1.16: How do I switch between differents 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.
  • Some other ways are described [here].

Q1.17: How do I make an AVS-file ?

A: See Q1.19 (thus using the text editor you prefer).

Q1.18: Where do I save my AVS-file ?

A: Anywhere on your harddisk.

Q1.19: How do I know which version number of AviSynth I have ?

A: 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. The version number will be displayed.

Q1.20: Does AviSynth have a GUI (graphical user interface) ?

A: Several nice tools are available:

  • VirtualdubMod, see also Q1.9. 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.
  • [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].

Q1.21: I got the message "LoadPlugin: unable to load "xxx" is not an AviSynth 1.0/AviSynth 2.5 plugin" ?

A: You are using a plugin which is not compatiable with that version of AviSynth. Have a look at Q1.8.

Q1.22: How do I know which colorspace I'm using at a given place in my script ?

A: To see which colorspace you are using at a given place in your script, add:


... and AviSynth will give you much information about colorspace amongst other things!

Q1.23: I installed AviSynth v2.5 and DivX5 (or one of the latest XviD builds of Koepi), all I got is a black screen when opening my avs in Virtualdub/VirtualdubMod/CCE/TMPGEnc ?

A: Ok, apperently your video is not decompressed by DivX5 (or XviD). Go to your windows-dir and rename a file called MSYUV.DLL, or add the following to your registry file:


[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\!CurrentVersion\Drivers32]

Replace "divx.dll" by "xvid.dll" for XviD.

Q1.24: My computer seems to crash at random during a second pass in any encoder ?

A : AviSynth (especially v2.5x) 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.

Q1.25: VirtualdubMod, WMP6.4, CCE and other programs crash every time on exit (when previewing an avs file) ?

A: This problem arises if you got LoadPluginEx.dll (or WarpSharp.dll) of the WarpSharp package in your plugin dir. The solution is to move it outside the plugin directory and load it manually. I hope that the maker of this plugin also noticed this :)

Q1.26: Are there any lossless YV12 codecs, which I can use for capturing for example ?

A: There are several of them:

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Document last modified Fri, 24 Dec 2004 21:50:50