Independent drivetrains on tandem bicycle On a standard tandem frame, is it possible to build a tandem bicycle with independent drivetrains for the two riders? Is there a custom frame builder that would build a tandem like this?

I'm aware of the half-recumbent tandem that has independent drivetrains, but I'm specifically interested in the classic/normal tandem frame.

EDIT: By independent drivetrain, I mean that I would like each rider to be able to coast independently of the other. The cadence can remain constant between front and back when both are pedaling.
Here's a picture of a half recumbent tandem

from https://www.ucycle.com/merchant/2856/images/zoom/hase-pino-allround.jpg

Here is a link to a video of people riding a recumbent tandem.
https://binged.it/2TXkxJC
The video does a good job of explaining that the front crank has a freewheel mechanism that lets the riders pedal at different speeds. The front rider can also stop pedaling.

If this is what is meant as "independent drivetrains" then the functionality is in the crank rather than the frame itself.

The key to having a regular tandem like the recumbent tandem in the video is to find someone who makes a crank with a freewheeling chain ring. Like the old school Schwinn Suburban's from the late 70s with Shimano Positron FFS (Front Freewheel System).

Here's a link to a product for mountain bikes with a freewheeling chain ring
https://dirtmountainbike.com/news/hxr-easy-shift-crankset-allows-change-gear-without-pedalling.html

With this part - or something like it - any tandem frame builder should be able to get you going.