Incorrect blending when the chroma is subsampled.

The blend module does not correctly blend when the chroma (UV) is subsampled, introducing a lot of annoying aliasing.

A SSA samples showing the default when YV12 is used as video output format (XVideo)

Added attachment:

• zoom.ass

Here's a fix. This can probably be done a bit more efficiently by working on 2x2 blocks at a time instead of pixel by pixel and extra handling of chroma. However it's only slightly slower.

Added attachment:

• 0001-blend-subsample-chroma-correctly-when-blending-rgba-.patch

Color is fixed in master and 1.1.10

added Component::Video: subpictures label