How to remove Green Sidebars in Video Sink (GStreamer, vaapisink)

[David Manpearl]

When I display a 4:3 aspect ratio video in a 16:9 display screen in
fullscreen, the result display shows bright green sidebars OR places the
4:3 video in a random location within the larger display.
How to remove the green sidebars?
Or, How to center the video in the display?

GStreamer 1.14.4 on Intel Cherrytrail hardware on Debian GNU/Linux 9
(stretch).

Same results with vaapisink or waylandsink.
Same results with "fullscreen=true" or setting the sizes explicitly via
videoscale or vaapipostproc.

Example pipelines:

Green sidebars:
gst-launch-1.0 videotestsrc ! vaapipostproc width=1920 height=1440 !
vaapisink fullscreen=true

Green sidebars:
gst-launch-1.0 videotestsrc ! video/x-raw, width=1920, height=1440 !
vaapisink fullscreen=true

Dark sidebars (good), but can't horizontally position the window (bad):
gst-launch-1.0 videotestsrc ! video/x-raw, width=2880, height=2160 !
vaapisink

Dark sidebars (good), but can't horizontally position the window (bad):
gst-launch-1.0 videotestsrc ! video/x-raw, width=2880, height=2160 !
waylandsink

Videobox removes green sidebars (good), but performance hit (bad):
gst-launch-1.0 videotestsrc ! vaapipostproc width=1920 height=1440 !
videobox left=-320 right=-321 top=-1 ! vaapisink fullscreen=true

Videomixer provides similar performance degradation to Videobox as would be
expected.

Does anyone know how to remove the green bars without degrading performance?

Thanks!
 - David
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