I'm working on a kiosk which will regularly record short clips of video. At a
certain point in the sequence I open the video grabber and start previewing
the video; subsequently I start recording, then switch back to preview, then
close the VG altogether. Rinse, repeat.
Each time the VG is initialised, the VG rectangle goes white for approximately
three quarters of a second. Unfortunately in our design the screen is mostly
very dark, so the white shows up really strongly.
I've tried various things to reduce this - eg tying the video grabber to a
featureless borderless sub-stack the size of the video rectangle, and hiding
it, putting it offscreen, or putting it behind the mainstack while it
initialises. Most of these fail altogether.
The best I've managed to do is with the substack hidden; initialise the VG,
start previewing, and give it a full second before showing the substack (I've
noticed when the video actually starts, it also sometimes (?) appears dark,
and takes a few frames to come to a balance - presumably this is down to the
camera). Doing it this way I still get a white flash, but it's extremely short.
Although the substack is hidden, the flash appears where the substack is. So
I can manipulate the position of the flash, by moving the hidden substack
before I initialise the VG, and then moving the substack into the correct
position immediately before making it visible, after the VG has had its second
to 'warm up'. If the hidden substack is moved entirely offscreen, then the
whole thing fails; there's no flash, but when the substack is moved back into
position and shown, there's no video either, just a white rectangle. However,
if the hidden substack is partially onscreen, partially off, then the white
flash is limited to the
area-that-would-be-visible-if-the-substack-wasn't-hidden, and when the
substack moved to the correct position and shown, it all works correctly.
Hence the best I've managed to do is move the the substack so far off the
bottom right of the screen that there's just one pixel it of it onscreen; the
white flash is then reduced to a single pixel. Unfortunately because the
overall design of the kiosk is very dark, this is still visible - but a lot
less intrusive than what we started with. Although having to warm up the VG a
second before I want to use it is a bore I can easily fairly easily accomodate
this within the control flow.
So I do now have a reasonable workaround (confession: I hadn't got this far
when I started writing this email). But is this the best one can do? Is
there a better approach altogether that I've missed?
(The obviously completely different approach is to initialise the VG once when
the kiosk launches, and leave it running all day, hiding and showing the
preview/record stack as necessary. However this is going to be in a
high-traffic and high-profile location, from launch, and there's not long
before launch; so I'm nervous about doing this without more time for soak
testing, given various anecdotes I've heard about drifting sync etc. But if
there's contrary experience that this can work reliably, I'd be interested to
hear about that also.)
Many thanks,
Ben
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