How will The Sound of Music Live work?

And if you think it'll be anything like the version in the USA with American Idol Carrie Underwood and True Blood's Stephen Moyer taking the leads, you're very mistaken.

Because according to Giedroyc, and everyone we meet on set, this Sound of Music is a very different animal.

Will it be like the movie?

Don't expect to see a rehash of the big screen hit on your TV screens. The Sound of Music Live is leaving the film and taking inspiration from the stage musical.

There will be songs you've never heard before, familiar tunes in a different order, and events might unfold in locations where you'd least expect them.

That's not the only change you'll notice though. Giedroyc describes the production as a much more politically fuelled tale, focussing on the real issues Austrians faced as Hitler and the Nazis prepared to invade.

Oh, and Katherine Kelly's Baroness Elsa von Schraeder is very different to the woman we meet in the film. Tune in to see what we mean...

So it'll be just like a night at the theatre then?

Nope. Not at all. ITV are going to film it in the same way they'd film a drama like Mr Selfridge or Downton Abbey. They'll be using 17 cameras, some of which will zip in and out between the actors as they deliver their lines and their songs on delightfully detailed sets.

Maria's quaint bedroom is beautifully simplistic, and backs on to the famous theatre in which the von Trapps give their final Austrian performance. It wasn't quite finished when we clapped eyes on it, but the Nazi banners hung ominously in the background.

And that's just the first sound stage we visited.

The next stage hides an incredibly realistic and rustic Abbey, surrounded by real trees, real grass, and a backdrop that takes you straight out onto the famous hills.

Set designer Tom Burton and his team have been busy.

The final sound stage is home to Villa von Trapp, its sprawling gardens, and the famous staircase where seven siblings will assemble to say so long, farewell, auf wiedersehen, goodbye.

There's not much room left for an orchestra though, so they've had to pre-record the music.

But they're still singing live?

Oh yes they are. Kara Tointon and Julian Ovenden were busy warming up their vocal cords in the garden when we gathered for an impromptu performance from the pair.

Who knew Dawn from EastEnders and the pig man from Downton Abbey could sing?

How are they going to get from set to set?

The actors and camera crews will need to run from sound stage to sound stage, so the powers that be at ITV are hoping for good weather on the big night. And that's where the ad breaks come in.

"Obviously we're using the ad breaks, apart from anything else, to move the actors from one set to the other, so it had to be very carefully plotted," says ITV’s Director of Entertainment and Comedy Elaine Bedell. "That took a lot of time actually, to sort of scene set and work where the ad breaks should come."

"We've absolutely got the drama right; we had to go through it in real detail," says Executive Producer Fiona Clark. "We're timing like mad and have really great teams for quick changes."

What happens if something goes wrong?

The show must go on, but they're as prepared as they can be. Each actor will have two microphones, and there'll be two music tapes running, just in case one goes down.

And there are understudies waiting in the wings, should The Captain or Maria fall ill. They're "names from the world of musical theatre", says Fiona Clark. "No surprises."

The Sound of Music Live airs Sunday 20th December from 7.30pm on ITV