Set a sync point to possibly wait on at a later time.
Insert a wait into context's command stream ensuring all previous OpenGL commands before sync_meta have completed.
Perform a wait so that the sync point has passed from the CPU's perspective What that means, is that all GL operations changing CPU-visible data before the sync point are now visible.
#GstGLSyncMeta provides the ability to synchronize the OpenGL command stream with the CPU or with other OpenGL contexts.