This was a Russian short called "Gde eto vidano, gde eto slykhano" that was broadcast on the Festival in the late '70s under the name "The Show Must Go On". Lenfilm had all of the footage from the short removed from Youtube (including a clip I uploaded), but you can watch it here:
http://video.yandex.ru/users/alekx2016/view/698/#
It's a funny film, even if you don't understand Russian. :)