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Installation problems

If you got problems getting AviSynth to work at all, try the following script:


and open it in Windows Media Player 6.4 (it is a file "mplayer2.exe" located in "C:\Program Files\Windows Media Player", other versions of WMP will not work).

If that doesn't work, you can try the following:

  • Empty the plugin dir. of AviSynth: avs scripts or filters can cause this, especially in v2.0x.
  • Install HuffYUV: it can be that there is no decoder present which can decode your scripts.
  • If you use an encoding package (like DVD2SVCD, GKnot, DVX, ...) make sure that you use the version of AviSynth that came with that package: it might be that new versions of AviSynth are not compatible with the package.
  • Reinstall AviSynth: it might be that something went wrong with the installation.
  • If all of the above doesn't help drop a post in the [Doom Nine Forums].

Other problems

Creating scripts with AviSynth is not always easy, and sometimes AviSynth produces very strange results. This is a little guide to help you figure out the most common errors.

Write Simple

If AviSynth produces strange results, try simplifying your script. Try splitting up your script into as many lines as possible. This will help you identify your problem. For example:


return AudioDub(Blur(video, 1.5).Reduceby2().Bilinearrresize(512,384),Wavsource("file23.wav").AmplifyDB(4.5)

Is not as readable as




Blur(video, 1.5)





Furthermore it has the advantage, that you easier be able to:

  • Comment out a single line. This is good for testing the effect of a filter.
  • Get the proper error line, if there is a syntax problem.
  • Put in a return last any place in the script. This output the video at the current place in the filter.
  • Get an overview of the "flow" of the script. (Is it a good thing that the Trim command only affects the video in the clip above?)

Always check parameters

If you have a filter that gives you unexpected result, try using it with the simplest parameters. Always check the FiltersByCategory either on this homepage or in the documentation that came along with your AviSynth.

Be sure you use the same type of parameters as the ones described in the documentation. The most common error in this case is related to the first parameter in all filters, "clip". Be sure you understand how "implicit last" works. If you do not have a "last clip", most filters will fail with an "Invalid parameter" error.

"Filter does not return a clip" is reported if the output of your last filter is put into a variable, and there isn't any "last clip" . For instance:

video = AviSource("file.avi")

audio = WavSource("file.wav")

combined = AudioDub(video,audio)

Will fail.

This can be solved by:

video = AviSource("file.avi")

audio = WavSource("file.wav")


Where 'last' contains a clip, or:

video = AviSource("file.avi")

audio = WavSource("file.wav")

combined = AudioDub(video,audio)

return combined

Where the variable is returned, or even:

video = AviSource("file.avi")

audio = WavSource("file.wav")

return AudioDub(video,audio)

Test scripts using Virtual Dub

Always use VirtualDub or even better VirtualDubMod to test your scripts. This is what all AviSynth functionality is tested against. AviSynth does of course work with other programs, but if you get errors in other applications it's most likely not an AviSynth problem, but a limitation within the software you are using.

These limitations are mostly linked to:

  • Colorspace problems. The application you are using does not support the colorspace you are using.
  • Size problems. Some programs does not accept all sizes of images.

Go through the script step by step

As mentioned in "Write Simple" it is always a good thing to test every step of your script, if there are problems.

You can comment out a filter by placing a '#' in front of the line. That way it will be ignored by AviSynth.

You can put in a "return last" or "return myvariable" any place in the script.

At any place in the script you can add the Info() filter to get information about the image and sound at the current stage of the filter.

Check your plugin directory for AVS files

You must remember, that ALL avs files in your plugin-directory are automatically included in your script. This is a feature, to allow you to include your own functions, without have to copy/paste them into every script.

This also means that if you copy any sample scripts into your plugin directory they will always be included, and may generate errors. Therefore, remove any AVS files that comes with your plugins as examples. In general, any AVS file whose commands are not wrapped into functions will be problematic.

All other file formats besides AVS and DLL files are ignored, so you can safely leave your documentation there.

In AviSynth 2.5.0 and 2.0.8 avs files are no longer included by default - only files with the ".avsi" extension are autoloaded.

Use conservative image sizes

If you have problems with distorted images, try using conservative image sizes. That means, use sizes, where height and width are always divisible by 16. Using image sizes that are not divisible by 2 is in many cases problematic, and should always be avoided.

If you do however find that there is a problem with certain sizes of images, please submit a bug-report. See below how to do that.

Finally check the AviSynth Q&A

If you still got problems (loading scripts in certain encoders, or colorspace errors) have a look at the AviSynth Q&A, especially Q2.4.

Be also sure to check Known Bugs in the FAQ.

Reporting bugs / Asking for help

We will need many informations to be able to help you. If you don't supply us with that, there is a good chance that we won't be able to help you or locate the error.

Be sure to always include:

  • AviSynth version. (and date, if not a SourceForge release)
  • The simplest possible script for recreating the error.
  • The EXACT error message you get.
  • VirtualDub (Mod) version.
  • All information from Virtual Dub / File / File Information.
  • Used plugin versions.
  • Codecs and image sizes of input material.

Bug reports should be submitted at the [SourceForge Project page]. Be sure to check if there is already a bug summitted similar to yours - there might just be. Errors in external plugins shouldn't be reported here, but to the author of the filter.

A very good place to get help is the [Doom Nine Forums]. Be sure to search the forum before asking questions. Many topics have been covered there!

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Document last modified Wed, 30 Jun 2004 10:26:20