AFAIK - you've done the best that you can do with rev based hacks.
Maybe you could contact Kevin and ask for the source code? I think there are
a few other people that would really like this external improved and it
would make a great open source project - especially if you could put a small
ransom on it?
On 13 September 2010 12:32, Ben Rubinstein benr...@cogapp.com wrote:
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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