Peculiar performance with glvideomixer

[dbousamra2]

If I have this pipeline

gst-launch-1.0 \
  glvideomixer name=mix sink_0::alpha=0.5 sink_1::alpha=0.5 ! videoconvert !
fpsdisplaysink video-sink="xvimagesink" \
  videotestsrc pattern=ball is-live=true ! \
   
video/x-raw,format=AYUV,framerate=\(fraction\)$FPS/1,width=$WIDTH,height=$HEIGHT
! \
    mix. \
  videotestsrc is-live=true ! \
   
video/x-raw,format=AYUV,framerate=\(fraction\)$FPS/1,width=$WIDTH,height=$HEIGHT
! \
    mix.

If you try this pipeline with `WIDTH=2560` `HEIGHT=1440`, `FPS=30`, it
behaves perfectly. No dropped frames, and FPS at 30. But if you change the
FPS to 60, it completely breaks, and not only does it start dropping frames,
the 2nd mixed in stream just stops.

If you try `WIDTH=3840` `HEIGHT=2160,` `FPS=30`, the 2nd stream doesn't even
render properly. If you lower the FPS a little to say 20, it behaves fine.
If I go to 25 the 2nd stream stops entirely.

I imagine those exact values above are specific to my machine, and you may
have to play with them to see the same behaviors. Does anyone have an
explanation for these behaviors?



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