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/CropRel  
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.* Chroma shift currently not supported
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