since 

mesa commit     34f46348438b29e20d06cca312616cfba8ee05f6

For putimage call, if image format is yv12 (or IYUV with U V field swap) and
surface format is nv12, then we need to convert yv12 to nv12 and then copy the
converted data from image to surface. We can't use the existing logic where
surface is destroyed and re-created with yv12 format.

v2 (chk): fix some compiler warnings and commit message 

mpv --vo=vaapi will produce corrupted output without the new env
VAAPI_DISABLE_INTERLACE=1

This only applies to s/w decode as hwdec uses nv12 and avoids the conversion.

Gstreamer vaapisink is not affected as (from what little debugging I did) it
doesn't seem to use interlaced buffers doing putimage.