I have taken a few commercial flights with my wife on which our plane was equipped with seatback entertainment systems. We sometimes watch the same movie at the same time so we can have a shared viewing experience, but there’s a peculiar quirk that makes this challenging. I can push play on the two screens simultaneously, so that both movies start at exactly the same time - but as time progresses, one of the movies plays faster than the other, developing a discrepancy of perhaps one second for every minute of video. So every five minutes or so, I have to pause the faster-playing screen to let the slower-playing screen catch up. If I don’t do this, then before long we’re not getting laughs or surprises at the same time; it’s like we’re watching two separate movies.
So what’s going on with these video systems? They are ostensibly identical, but they definitely behave differently. Are they dropping frames, or playing back the video at two different frame rates? And in either case, why is this happening?
I have flown with an airline that had a “share screen” function in their entertainment system that would duplicated what you were watching on someone else’s screen. I’d be interested to know if it suffers the same kind of sync issues.
Edit: when this happened, were there any inflight announcements? Could the different screens have paused for slightly different times?
There are occasional inflight announcements that pause the video, but the behavior I describe happens even in the absence of those announcements. It’s happened on several flights, so it’s not just a single aircraft. Also, it’s not a “sometimes you’re ahead/sometimes you’re behind” thing: one of the video screens is consistently slower than the other.
If it matter, this is on Delta Airlines. I don’t think I’ve ever seen the share function you describe, but I expect that would solve the problem, so I will look for it on our next flight.
I flew Delta recently and there was a malfunction in the seatback entertainment system so that they had to reboot it. However, the seats that had the malfunction were in the same line (not row) of seats. That is, all the “A” seats malfunctioned but not the adjacent “B” seats in the same row. This implies to me that the same lines may be getting somewhat different feeds. (Admittedly, I don’t know how the system is actually set up.)
I agree
My SWAG. Since each screen can be controlled separately then it looks like each screen is running an instance of the same program.
You would expect the programs to operate (and display) at the some speeds.
Except that the programs are doing other things too. Constantly checking the status of controls, running comparisons for audio and video sync, monitoring etc. Those other processes most likely are run by other programs which are polling all screens and most likely automatic and crew action items (Pilot pausing your video to give instructions)
My SWAG is that the polling systems have a hierarchy method of checking physical buttons and such. Your screen1 is benefiting from being further up the list than your screen two.
Do the movies start at specific times, or is it a video on demand kind of system?
But I think BubbaDog has it. It is probably both load on the computers controlling the display and delays due to network traffic on the network bringing the content from the server to your seat. If there are different networks for seat A and seat B, which would make routing easier I’d think, there could be more people watching on one of the networks, and thus more traffic and more congestion.
Not exactly the same thing, but I was recently testing the battery life on two (different model) cell phones by playing movies on them. Both started within a fraction of a second of each other. They began to noticibly drift apart within probably less than 20 minutes. (But nothing like a second per minute.)
It’s video-on-demand; you select a video from their collection and push start when you’re ready to watch, and of course you can also pause/rewind/fast-forward at any time.
Colibri’s report was interesting, i.e. that columns of seats (rather than rows) appear to be ganged together on one (sub)system; this could explain why my movie consistently played faster (or slower, can’t remember which) than my wife’s video. I just assumed that everything would be adhering to something like an HD video standard, spewing frames at a very specific frame rate; hadn’t occurred to me that any given system might be delaying individual frames by a smidge.
Since you bring up phones, I have a Samsung tablet and an iPhone with service being provided by Sprint. As I type this, the time on the iPhone is displayed as 3:34 p.m., while the tablet informs me that it’s 3:29.
Wiring the plane with straight line cables with a drop at each seat would seem much simpler than going across. And your seatback monitor can only display frames as fast as it gets them. The few times I’ve used this I’ve never noticed any buffering, which would require more storage at the seat in any case.
I don’t know anything about these systems but I was curious and googled a bit. Looks like a common architecture for non-fiber based systems was as follows (pretend the dots are spaces and | are cables):
media server
…|
…Switch
|…|
|…|
Zone/…Zone/
Area…Area
Box…Box
|…|
n Seats…n Seats (each seat has a linux or android display device)
|…|
|…|
Zone/…Zone/
Area…Area
Box…Box
|…|
n Seats…n Seats (each seat has a linux or android display device)
etc.