GL support is available for MPEG/VCD playback. This support is not recommended
for most people, as if your chipset supports 3D acceleration, it likely supports
the far superior XVideo extension. (Superior at least
for standard video playback. The GL support is much less stable and
GL support has been primarily developed on a Voodoo3 with XFree86 4.0.x
DRI (Mesa 3D) and a Sun Elite3D with Solaris 8 (OpenGL). For Voodoo3 the XVideo
extension can work, so Voodoo3 is not a recommended platform for this option.
The primary thing that occurs to me is older, 3D only Voodoo cards
and non-XFree86 setups, such as Solaris.