I'm not sure about the merit, though it does print nice numbers if debug
output is enabled.
Basically, this tries to achieve similar results as the glFinish()
business, but again it entirely depends on the drivers whether this
does anything meaningful, or whether it's actively harmful.
It seems that at least on nvidia systems with composting disabled, we
can get it to block deterministically on the actual vsync event, which
should improve framedropping.
Notably, we now conform to SMPTE 428-1-2006 when decoding XYZ12 input,
and we can support rendering intents other than colorimetric when
converting between BT.709 and BT.2020, like with :srgb or :icc-profile.
This add support for reading primary information from lavc, categorized
into BT.601-525, BT.601-625, BT.709 and BT.2020; and passes it on to the
vo. In vo_opengl, we always generate the 3dlut against the wider BT.2020
and transform our source into this colorspace in the shader.
