JavaScript Environment

This document describes the contents of the JavaScript environment avaiable when running within JSVSynth.

The following documentation is a bit speculative. Check out the AviSynth object documentation for the most up-to-date version.

AviSynth

The AviSynth object is effectively the "namespace" for various AviSynth functions and contains the following:

• AviSynth.ColorSpace - a color space inside AviSynth, see AviSynth.ColorSpace
• AviSynth.Filter - constructor for creating custom AviSynth filters, see the "Filter" section below for details
• AviSynth.VideoFrame - class that provides direct access to video frame data. Instances can be created directly in order to create blank frames or be pulled from an existing clip.
• AviSynth.functions - a collection of AviSynth functions. This allows accessing and setting AviSynth functions from JavaScript. Note that functions and variables have different namespaces in AviSynth, while they share a namespace in JavaScript. This only access functions. Also note that the function and variable namespaces in AviSynth are case-insensitive. This collection reflects that - AviSynth.functions['foo'] is the same as AviSynth.functions['FOO'].
• AviSynth.variables - a collection of AviSynth variables. This allows accessing and setting AviSynth variables from JavaScript. See the above note.

avs

avs provides access to both AviSynth functions and variables. In AviSynth, functions and variables exist in separate namespaces. Which one gets used is based on the syntax. This means that the following code is perfectly valid AviSynth:

foo = 1
function foo() {
    return 2
}

Both values still exist and can be used. However, in JavaScript, there is no separation of functions and variables. This means that there's no (good) way to offer both a function and a value back from AviSynth.

Instead, currently, if a function exists, it will "mask" the variable of the same name. This means that while you can do something like:

blankclip = "Hello"
JavaScript("""
    console.log(AviSynth.variables.blankclip + " World!")
    avs.BlankClip()
""")

And access both the variable and function despite them having the same name.

Note that attempting to set a function to the AviSynth.variables collection will instead coerce the value to a string, which probably isn't what you'd like.

Setting a non-function to the AviSynth.functions on the other hand will raise an error.

Filter

AviSynth.Filter lets you write a filter using JavaScript:

var myfilter = new AviSynth.Filter(avs.BlankClip());
myfilter.getFrame = function(frameNumber) {
    return this.child.getFrame(frameNumber);
};

At its most basic, an AviSynth filter is something that produces frames. In the above example, frames from a BlankClip() are being passed straight through to the other end.

Things that will be done ... later

• Allow a filter to be created without a "child" filter. At present, you always have to wrap an existing filter, which is used to determine what fields are present.

VideoFrame

A video frame can be produced by a clip using the getFrame(framenumber) function. (This can be used on literally any clip, and, in theory at least, this should always produce results.)

The video frame provides raw access to the pixel data for a frame. There are two different types of video frame objects that can be returned: one for interleaved access, and one for planar access. The planar access one is slightly weirder because you access the Y, U, and V frames seperately.

Note: Once a frame has been returned from a filter, it will be "neutered" and any remaining references to it will no longer be able to access data. If you access a frame but do not return it to the filter, you should manually release() it when you're done with it. (If you don't, V8 should eventually free the video frame when it gets garbage collected. Unless you hold on to a reference. Don't do that.)