So no Bluetooth broadcast? I looked a few years back and was stymied as well. I think it stemmed from a commercial for something showing a indoor concert show thing with no noise, but the entire audience wearing wireless headphones. Seems like a thing that should exist.
There's probably some professional solutions, but it would require some ASIC or ARM based boards to handle encoding of audio to multiple BT radio chipsets
I'll investigate and let you know if I find anything.
Another solution would be to use a Pi4 with a usb hub and several cheap BT 5.0 usb adapters.
Found a solution (up to 10 devices) but it's actually an analog audio splitter to several BT transmitters (each can handle two BT headphones)
Yeah, that's from last year and BT LE (Low Energy) is part of the BT 5.0 specifications.
I have yet to see a single transmitter that does it.
So the KOKKIA solution might be a more viable one, atm. If one transmitter becomes faulty, you can still use the others (waiting for a replacement).
I've seen that commercial and it brought it mind. I have a teacher friend who was asking this for a bunch of kids and all I could see was some old Sennheiser headphones and she wanted them to bring their own.
You could do a stream service but creates a delay and could be more cumbersome for the teacher to setup.
Found two more, but not sure if they can transmit audio at the same time:
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