This plugin takes I420/YUV and appends an alpha plane to give YUVA/A420
to round the corners analogous to the border-radius in CSS. Other video
formats like NV12 not supported yet. Support for other planar formats
will follow.

Not all ways of specifying border-radius as in CSS are implemented at
the moment. Currently, we only support specifying it in pixels and it
gets applied uniformly to all corners.