libvorbis complains "more samples than frame size"
Solution 1:
Use -f lavfi to indicate that the following inputs are filters. Because you have two distinct inputs use two -f lavfi.
ffmpeg -y -f lavfi -i "smptehdbars=size=1280x720:rate=30000/1001" -f lavfi -i "sine=beep_factor=2" -c:v libtheora -c:a libvorbis -t 3 output.ogg