Mexican Day of the Dead in America (video)

What are the origins of Mexico's pre-Mexican -- actually Mesoamerican (Aztec, Maya, Toltec...) -- Dia de los Muertos or "Day of the Dead"? It is not the Mexican version of Halloween, Ireland's Samhain, or Japan's Obon. But it is similar, as all ancient cultures had regard for the ancestors, the dead (pretas, relatives, spirits, hungry ghosts), the dearly departed. The BBC and PBS give their take on this ancient pre-Mexican celebration that comes when the veil is thin between the worlds of the seen and unseen, as Buddhism would describe it.