vaapipostproc can not convert packed RGB24 to other format.
gst-launch-1.0 videotestsrc ! video/x-raw, format=RGB, framerate=30/1, width=640, height=360 ! vaapipostproc ! glimagesink
failed because lack of packed RGB24 format support in vaapi
gst-launch-1.0 videotestsrc ! video/x-raw, format=RGB, framerate=30/1, width=640, height=360 ! vaapipostproc ! glimagesink
failed because lack of packed RGB24 format support in vaapi