A pretty clear and very audible video has emerged of the filming of the song "Do You Hear the People Sing?" with Hathaway and Hugh Jackman "singing" along. It's central to the musical, and one of the most recognizable songs, first appearing at the end of the first act and during the finale, which this scene appears to be from. While there are many reports that singing was going to be recorded live, here everyone is performing to playback, likely due to the massive size of the set piece which would make arranging a live recording a total nightmare. It's an impressive thing to watch, and clearly the scope of the story will be making its way to the big screen in spades.