By Jill Serjeant NEW YORK (Reuters) - U.S. television was alive with "The Sound of Music" on Thursday as country singer Carrie Underwood and "True Blood" actor Stephen Moyer starred in a live version of the classic musical about an aspiring nun who falls in love with an Austrian captain. Filmed on vast movie sets and with lavish costumes but without an audience, the NBC television broadcast harked back to the traditions of the 1950s and 1960s when live musicals were often shown on American television. Thursday's three-hour show was based on the 1959 stage version of the Rodgers and Hammerstein show rather than the Oscar-winning 1965 musical starring Julie Andrews. After heavy promotion for weeks, the live broadcast was the No. 2 topic on Twitter on Thursday, behind the death of South African anti-apartheid hero Nelson Mandela.