I'm trying to use the GL_OML_subsample extension to enable downsampling from a 4:4:4 YCrCb buffer to a 4:2:2 YCrCb buffer. According to the OpenML spec, enabling this extension allows use of the FORMAT_SUBSAMPLE_24_24_OML enumerant to properly pack/unpack the pixel data. However, my video card (nVidia 6000 series, latest 84.21 drivers) does not seem to support this OpenGL extension, which is surprising considering that it is in the OpenGL 1.2 spec.

How is this extension typically accessed? Is there some additional library that I need to use, or is there another recommended way to subsample pixel data?