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AviSynth - A wolf in sheep's clothing!

Avisynth is the source of a legend amongst internet users that there is a dark, complex, highly functional, but very obscure free video editing program out there. It does indeed exist and it is called Avisynth.

The reason it's so dark and obscuer is that it is designed with speed in mind. To that end it has no user interface and works directly off a command line. In addition to that it actually uses text files as inputs!

"How can this be?"

Well, according to the Wiki

"AviSynth works by faking AVI files. That means that AviSynth script files work in principle with all media applications and players capable of opening AVI files. What you might see in real life is that not all applications treat video files like they are supposed to. (For instance, Ligos MPEG encoder will not let you choose anything but straight AVI files in the file selector. But if you load an AVI, and manually change the name in the filename box to .AVS - it works perfectly.)

Because AviSynth works like a frameserver your filters are being applied 'on-the-fly'. That means that when a program that has opened an AVS file requests frame 303, it is read from the source, the filters are applied before the frame is delivered to the program."

Frameserving

A frameserver is basically something that feeds video frames directly to another application. In the case of AviSynth the frames can be manipulated prior to being served so that the resulting file is managed twice in one step.

Imagine, for example, that you were using something like Wax to edit your video, but the video you were actually editing wasn't Wax accessible (maybe it was in the wrong format or the wrong size). If you frameserved it through this tool you could take that 'invalid file', use AviSynth to reformat it and change its size (through a crop or a letterbox, for example) and pass the manipulated file to Wax where it could be worked on.

Uses

In general AviSynth makes it very easy to adjust the look of your video, and doing fast and easy editing. It is not easy to use it for cutting your videos, or doing advanced post-processing. AviSynth is useful, however, to prepare your video before you cut it in one of these programs, and adjust color, remove noise, crop / resize.

In general this is a very good tool when having to compress video. Many filters are written specifically for tasks regarding video pre-processing when compressing or recompressing video. There are many well written plugins to help you make your movie more compressible, reduce noise, adjust color and resize your source material. And because it works as a frameserver, you often do not need a temporary file before you compress it.

The user interface

As mentioned already, there is no user interface for this tool. It works through the creation of scripts (text files) which are called from a command line for execution. Bt there are a number of enterprising people who have created GUI's that will effectively take the place of the script. By understanding what you want to do with the file they will give you a graphical interface that will wrie and execute the script for you automatically. Examples of this are:

VirtualdubMod
DVX
AVSGenie
TMPGEnc

The functions

There are literally hundreds of functions that this tool can perform. Some, such as colorYUV will take the colour space of your video file and convert it to YUV format (This is, basically the same colour space that motion picture film works on), others, such as Overlay will layer two clips on top of each other using different methods

Acceptable formats

AviSynth will accept input in many formats. The limitation is the codec set-up on a user's machine. For MPEG input a plug-in is needed which will recognise and translate this. This is useful if you want to input something from a DVD you have purchased.

Summary

A very complex, but useful tool. Once you get used to the concept of scripting (and there are many examples out there) to assist you, it is possible then to do some fantastic things with your video.

Not a good tool if you want a nice graphical interface to be able to cut and paste your video together, but for minor manipulations and some fantastic image processing, this is a great tool to have.

Click here to go to the AviSynth Wiki
Click here to see a number of scripting examples
Click here to download AviSynth

Click here to return from Avisynth to free software page

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