Hi Karan,
I'm trying to create a simple live video DJ application. Basically,
it take 4 inputs from 4 cameras, and allows me to switch between
them (nothing special). I have the quartz composer part done, but
now I need to put it in an application.
Having never really worked with PBuffers or live cameras (I have
messed around with QCRender), I need some help.
1) I'm using quartz composer to render the video to be displayed at
1024x768, with each of the 4 inputs showing below it at 256x192. My
idea is to render this all in a viewport of 1024x960, and then crop
it and put each section into a window, scaling the large video to
also put a preview onto the controller screen. Is this the best way
to do this, and how do I go about the cropping and embedding?
You can indeed render it all in a PBuffer and then show subregion of
the associated textures in NSOpenGLView, after making sure that all
contexes are shared. You can also have one composition + QCView per
window; this should be as fast or faster, and easier to do.
2) I know that uncompressed video takes up a lot of space over
firewire. For 4 cameras that send video at an unknown size (I think
they'll be analog, so they'll be through component cables), what do
I need to do to make sure that I can get all the various streams
without delay and at at least 1024x768? Is there anything I can use
(some sort of hardware) so that I don't have to potentially buy an
extra firewire card for my computer? Or will this not be a problem??
If you have 4 firewire cameras sending 1024x768 at 30fps that will be
indeed be a lot of data to process. That won't fit in a FW400 bus,
maybe not even in a single FW800 bus. From memory you can fit 3
640x480 streams at 30 fps on a FW400 bus, they have some graph on
pointgreyresearch.com that you might want to check out. You need also
FW800 cameras, as one FW400 peripheral on a FW800 will make the bus
run at 400Mb/s.
Anyway, I don't see how you'll do without an extra card.
But all that is more a question for Quicktime or Firewire people.
3) I want to have some way of creating a table in the application
that you can put data in, that will be sent to the quartz
composition for use whilst rendering. I need it to be able to
reorder the rows, but other than that I just need to be able to send
all the data in multidimensional arrays. I know of the Chart
application from the examples, but how do I enable reordering?
The chart is reading xml data. Either you reorder the xml data from
your app and pass it to QC, either you do it from within QC by
changing the indexes given to the Structure Index Member patch within
the iterator (0->1, 1->2 and 2->0 for instance).
4) The video input patch in quartz composer has that wonderful input
selection tool, but how do I get that in my application? Once again,
I know there's an example of it, but I can't make heads or tails of
how it's worth. If someone can give me a prod in the right direction
on this, I can probably take it from there.
You can't change patch settings programmatically since you can't
publish them, so you must save the inputs in the composition, or feed
the frames yourself as you might have seen in some examples and do the
input selection in your code.
Hope this helps,
Kevin
---------
Kevin Quennesson
Quartz Composer Team Apple Inc.
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