Edit your config.txt to force output to composite

When running omx player make sure to specify the output display, it doesn't automatically default to the display that is specified in the config.txt

/usr/bin/omxplayer /home/pi/wk-portraits-screens/starfield_render.mp4 --loop --no-osd -o local --display=5

Notes

--no-osd = hides any display overlays when looping the video

-o local = specifies that it is to output audio to the display in the config.txt

--display=5 = specifies the composite display