VapourSynth functions

Introduction

VapourSynth provides a number of functions that you can find in the Function Reference.

At the end of the day, these are just filters included in a plugin named std. The source code for these filters is in simplefilter.c.

Most of them work

Using a filter

VapourSynth.nim treats std plugin as any other plugin. It is already wrapped in std.nim and you don’t need to do anything special to use it.

For instance, in order to apply the Transpose filter:

import vapoursynth
Source("video.mkv").Transpose.Pipey4m

How can I pass parameters?

The way I wrap the functions is that optional parameters can receive none or some value. By default, I am passing none to all the optional parameters. Optional parameters requires importing the options module, which provides the keyword some. If you want to pass something different you have to do it like this:

import vapoursynth, options
Source("video.mkv").Bicubic(width=some(320), height=some(200)).Pipey4m

In Nim, it is equivalent doing: some(320), 320.some and some 320 so you could write:

import vapoursynth, options
Source("video.mkv").Bicubic(width=320.some, height=200.some).Pipey4m
                                  ^^^^^^^^         ^^^^^^^^

You could create a custom function making this parameters mandatory. This might be useful if you are going to call the same function with the same signature many times (and you want to avoid writting some many times:

import vapoursynth, options
proc myfilter(vsmap:ptr VSMap, w:int, h:int):ptr VSMap = 
  return vsmap.Bicubic(width=some(w), height=some(h))

Source("video.mkv").myfilter(320,200).Pipey4m

All the filters in VapourSynth.nim, has a first argument typed ptr VSMap and returns a ptr VSMap. This allows chaining functions.

proc myfilter(vsmap:ptr VSMap, w:int, h:int):ptr VSMap =
                    ^^^^^^^^^                ^^^^^^^^^

We can improve the readability by calling the filter with (w=320,h=200):

Source("video.mkv").myfilter(w=320,h=200).Pipey4m

Some notes on Nim

Nim is typed. So you can avoid some erros by taking advance of it. For example, you could define myfilter to take Natural (which includes only integers equal or greater than 0) instead of int.

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