std.MaskedMerge(clip clipa, clip clipb, clip mask[, int[] planes, bint first_plane=0, bint premultiplied=0])

MaskedMerge merges clipa with clipb using the per pixel weights in the mask, where 0 means that clipa is returned unchanged. If mask is a grayscale clip or if first_plane is true, the mask’s first plane will be used as the mask for merging all planes. The mask will be bilinearly resized if necessary.

If premultiplied is set the blending is performed as if clipb has been pre-multiplied with alpha. In pre-multiplied mode it is an error to try to merge two frames with mismatched full and limited range since it will most likely cause horrible unintended color shifts. In the other mode it’s just a very, very bad idea.

By default all planes will be processed, but it is also possible to specify a list of the planes to merge in the output. The unprocessed planes will be copied from the first clip.

clipa and clipb must have the same dimensions and format, and the mask must be the same format as the clips or the grayscale equivalent.

How to apply a mask to the first plane:

MaskedMerge(clipa=A, clipb=B, mask=Mask, planes=0)

How to apply the first plane of a mask to the second and third plane:

MaskedMerge(clipa=A, clipb=B, mask=Mask, planes=[1, 2], first_plane=True)

The frame properties are copied from the first clip.