Production Advice claims singer performed live and was not miming
Singer reportedly decided at the last minute not to sing live
The vocalist appeared on the steps of the Capitol to sing the US national anthem
Alicia Keys, James Taylor, Katy Perry and Fun. also appear on the 16-track Spotify playlist
US superstar set to sing live at annual awards ceremony
Singer pulls in hip-hop heavyweights for the follow-up to '4'
She will sing the US National Anthem at the Capitol in Washington, DC
Pepsi are staging a contest to find fans to dance with the star during her half-time show
Will Ferrell, Jamie Foxx among stars in video plea to US government in wake of Newtown school shooting
The singer's face will appear on a limited edition range of drinks cans