My pal Shelly Goldstein pointed out to me the probable reason that the Barbra edition of Mr. Corden's Carpool Karaoke had her driving him around instead of, as usual, putting James in the driver seat. Barbra always insists on being photographed from what she considers the better side of her face. In order to do that, she had to be on right side of the screen facing left…which means she had to be behind the wheel. Bill Maher, when he had her on, did what I think was his first-ever one-on-one interview with a guest where he was on the left. (Bill Maher is usually on the left but you know what I mean…)
A friend of mine who works at CBS and asked that I not quote him by name, wrote to tell me, "Every time I see one of those Carpool Karaoke bits, all I can think of is Craig Ferguson watching it and fuming that his budget for a week of shows was roughly what Corden gets to spend on one bit." Probably an exaggeration but not by a huge amount.
And a third friend, Marc Wielage, sent me the following. Marc knows more about video and production than anyone I know…
For insurance reasons, they do generally do tow cars on projects like this, but it's possible for some they kept it simple and did it as you say: had Corden drive and then just "caravan" them off to prevent any potential problems. But given that Ms. Streisand is 76 and already looks nervous, instead of letting her drive I would tow it as a "picture car."
Microphones are generally hidden in the visors. Musical playback is usually wireless, going to small receivers that the actors have strapped to their waist, and then the signal is fed to their ears with earbuds (and that can be done wirelessly as well). That way, the car interior mics don't pick up any leakage from the instrument track.
I would bet there's a sound person and a director in the car just ahead of them, monitoring sound & picture (respectively). If they're towing the picture car, they would just run wires from the picture car to the camera car. If there's no towing, you could do it wirelessly but they generally have to cheat by putting transmitting antennas on top of the car. They work around this by shooting exterior "beauty shots" of the car driving down the street without the antennas.
They can record both the new vocals and the existing instrumental backing with a multitrack recorder, usually battery-operated Sound Devices or Zaxcom recorder. Multiple takes are not a problem, and often they'll do pickups if either of them hits a bum note. (BTW, Streisand is notorious for asking for a teleprompter, so I bet that was going on, too, so she'd have a safety net in case she forgot the lyrics.)
The camera part is pretty tough, since they generally run upwards of 6 or 7 GoPro cameras jammed on the side windshield roof posts, visors, and on the windshield itself down low. When cars are towed, they usually have a black tarp on top of the windshield to cut down on glare and they also bring in extra lighting to make the actors look better. Hiding this many cameras and lights and microphones in a car is tough. It's amazing it works as well as it does.
BTW, syncing up these cameras for editing in post is a bit of a nightmare, since they tend to run off-speed and aren't the greatest in terms of quality. But the Corden people have this down to a science.
This is more than you ever wanted to know, but that's basically what goes on.
In a follow-up e-mail to me, Marc added…
BTW, they may be using more sophisticated cameras than GoPro (a $400 camera), but that was the gist of how I've seen it done in the past. It's a very complex, messy procedure, because it's very tough on the editors to wrangle all the footage for editing. Corden has certainly pushed this idea beyond any level anybody has done before, certainly a lot more sophisticated that Jerry Seinfeld's Comedians in Cars Getting Coffee.
Okay, I have one more question: Why don't they pre-record the vocals and is it possible they did that in this case? Ms. Streisand is said to be a very poor lip-syncer but it can't be that difficult when (a) she isn't singing solo and (b) she's only seen in quick cuts. I'd think it would be easier to sync-up her voice to picture in post than it would be to do thirty takes driving around in a car if she wasn't happy with something. And she is famous for spending hours if not days in a recording studio doing take after take to get a song the way she wants it to be.
Dialogue and singing are quite separated in these bits. Why wouldn't they pre-record the singing? That would sure make it easier on the road.
Thanks to Shelly, Marc and the person who cannot be named. And I'll bet one of these days, Corden does one of these with Kermit the Frog and a back seat full of Muppets.