Avisynth functions and their VapourSynth equivalents

Avisynth	VapourSynth	Notes
AviSource	avisource.AVISource	Use FFMS2 instead when possible
DirectShowSource	none	There will be no source filter using DirectShow because there’s no real need for it. Use FFMS2 instead.
ImageReader/ImageWriter	imwri plugin
Import	none	See the documentation for Python’s import for scripts.
ConvertTo*	resize.Bicubic( format=vs.YUV444P8)	This also determines the resizer used for chroma resampling, if needed
ColorYUV	std.Lut/std.Expr	Do the adjustment yourself
GreyScale	std.ShufflePlanes	ShufflePlanes(clips=inclip, planes=0, colorfamily=vs.GRAY) Extracts the first plane. Y for YUV, R for RGB, planes=1/2 = U/V G/B
Invert	std.Invert
Limiter	std.Limiter
MergeRGB	std.ShufflePlanes	ShufflePlanes(clips=[R,G,B], planes=[0, 0, 0], colorfamily=vs.RGB)
MergeChroma/MergeLuma	std.ShufflePlanes	ShufflePlanes(clips=[Yclip,UVclip], planes=[0, 1, 2], colorfamily=vs.YUV)
RGBAdjust	std.Lut/std.Expr	Do the adjustment yourself
ShowAlpha/ShowRed/ ShowGreen/ShowBlue	std.ShufflePlanes	ShufflePlanes(clips=inclip, planes=0, colorfamily=vs.GRAY) Extracts the first plane. Y for YUV, R for RGB, planes=1/2 = U/V G/B
SwapUV	std.ShufflePlanes	ShufflePlanes(clips=inclip, planes=[0, 2, 1], colorfamily=vs.YUV)
Tweak	std.Lut/std.Expr	Do the adjustment yourself
UToY/VToY/*	std.ShufflePlanes	See GreyScale and the other examples
ColorKeyMask	std.Lut/std.Expr	Do the adjustment yourself
Layer	std.Lut2/std.Expr	Do the adjustment yourself
Overlay	std.Lut2/std.Expr	Do the adjustment yourself
Subtract	std.Lut2/std.Expr	Do the adjustment yourself
AddBorders	std.AddBorders
Crop	std.CropAbs/Crop
FlipHorizontal/ FlipVertical	std.FlipHorizontal/ std.FlipVertical
Letterbox	std.CropAbs+ std.AddBorders
ReduceBy2	resize.*	Too specialized to ever be included in the core
Resize (all kinds)	resize.*
Turn180	std.Turn180
TurnRight/TurnLeft	std.Transpose	Add std.FlipHorizontal/std.FlipVertical to create a true turn
ConditionalFilter	std.FrameEval	Can also substitute many of the other conditionals
Animate	std.FrameEval	Combine with python scripting
ApplyRange	none	Use python scripting instead
BlankClip	std.BlankClip
StackHorizontal/ StackVertical	std.StackHorizontal/ std.StackVertical