If you didn't know, 2015 Rio's Carnival will take place on February 15th and 16th. The famous parades of Rio’s best samba schools actually take place on the 15th and 16th but there are also the famous blocos. There are already many parades (the blocos) taking part on the streets of Rio's Zona Sul (South Zone). If you didn't get tickets, it's not too late to flight out there on a last minute ticket.
After Carnival in Rio de Janeiro, the most famous Carnaval festivals are the ones of Salvador and Pernambuco (Recife/ Olinda). I personally would try the Carnaval experience elsewhere but Rio as it has become way too commercialized.