I've seen this question posted elsewhere some years back but there was no satisfactory solution at the time and I have the same issue and wondered if there was something now available.
I'm looking to be able to attach two Android tablets to the back of the car head rests so that my two children can watch films on long journeys.
They both want to be watching the exact same video at the same time, and I want them to be as in sync as possible. The kids will be wearing headphones, the sound won't be coming out of the car's speakers. As we're in a car we also don't have a WiFi network to broadcast over. Pressing play simultaneously on the two devices is also not a viable option.
We have tried a single tablet setup held centrally between the two headrests but as the tablet sits at an angle to either child (about 45 deg) they have to turn their heads to see it and tend to lean forward so they can see it more straight on which means they're not sat in their child seats correctly and often pull their seat-belt off their shoulder without thinking. So from a safety point of view this just doesn't work no matter what we say to the kids. If the tablets were directly in front of them on each headrest this problem goes away hence the need for a two tablet solution.
I was hoping there might be a solution where both tablets have the same video files on them but control data is being sent from one device to another - master/slave style. Or, as we have a spare tablet could that be used as a server and broadcast the video from that to the two slave tablets in the back of the car? This would be the perfect solution as it would be controllable by someone sitting in the front.
Another thought was possibly creating a WiFi hotspot with the server tablet (as it's an LTE tablet) and broadcasting over that but is this wholly dependent on mobile signal and also would it eat into the data allowance?
So my question is are there any apps or other solutions that allow either of these scenarios? I have been looking on and off for months (whenever we're faced with a journey tbh) but just can't find anything that does the job.
Any help much appreciated.