In commit
> 956c4d0 gl/format: use our own GL format enum's instead of gstvideo's
the name and return type of gst_gl_format_from_video_info changed,
but some returns of the old type were missed. Here they are
updated to the correct type.
https://bugzilla.gnome.org/show_bug.cgi?id=780064
The base class is useful for having multiple backing memory types other
than the default. e.g. IOSurface, EGLImage, dmabuf?
The PBO transfer logic is now inside GstGLMemoryPBO which uses GstGLBuffer
to manage the PBO memory.
This also moves the format utility functions into their own file.
