Sing-a-long-a Sound of Music is... well. Let me quote:
Let's start at the very beginning. Have you ever been to a musical film and had an uncontrollable urge to burst spontaneously into song? Well here's your chance to give full rein to your vocal chords and share a few of your favourite things with fellow audience members.
The original Julie Andrews film with all songs especially subtitled for the occasion (though we know that most of you are word-perfect) so the whole audience can: Join in all your favourite numbers and sing-a-long-a-Julie! Boo the Nazis! Hiss the Baroness! Attend the ultimate communal karaoke event of the century!
It's not even live! It's just the film, with subtitles - why do people pay good money for this? I'm not sure I can think of anything worse.