Hm, 720x480 is not quite 4:3, though CEA 2 is reported as 4:3
tvservice -m CEA
Group CEA has 16 modes:
mode 1: 640x480 @ 60Hz 4:3, clock:25MHz progressive
mode 2: 720x480 @ 60Hz 4:3, clock:27MHz progressive
mode 3: 720x480 @ 60Hz 16:9, clock:27MHz progressive
mode 4: 1280x720 @ 60Hz 16:9, clock:74MHz progressive
mode 5: 1920x1080 @ 60Hz 16:9, clock:74MHz interlaced
mode 7: 720x480 @ 60Hz 16:9, clock:27MHz x2 interlaced
(prefer) mode 16: 1920x1080 @ 60Hz 16:9, clock:148MHz progressive
mode 17: 720x576 @ 50Hz 4:3, clock:27MHz progressive
mode 18: 720x576 @ 50Hz 16:9, clock:27MHz progressive
mode 19: 1280x720 @ 50Hz 16:9, clock:74MHz progressive
mode 20: 1920x1080 @ 50Hz 16:9, clock:74MHz interlaced
mode 22: 720x576 @ 50Hz 16:9, clock:27MHz x2 interlaced
mode 31: 1920x1080 @ 50Hz 16:9, clock:148MHz progressive
mode 32: 1920x1080 @ 24Hz 16:9, clock:74MHz progressive
mode 33: 1920x1080 @ 25Hz 16:9, clock:74MHz progressive
mode 34: 1920x1080 @ 30Hz 16:9, clock:74MHz progressive