[SML] Qlab and video

[Andy Lang]

On Sat, Oct 10, 2015 at 9:53 PM gbierly via Stagecraft
stagecraft at theatrical.net <http://mailto:stagecraft@theatrical.net> wrote:

While we are on this I would like to hijack this thread, I have been trying
> to research the best way to get multiple video outputs.  I would prefer to
> run two individual outputs out of an 2009 iMac.  I have an older Matrox VGA
> dual-head-2-go and I am having a harder time getting drivers to work.  I
> would prefer to edge blend two surfaces anyway.

Edge blending and using a Matrox are not mutually exclusive. QLab 3 allows
you to use partial surfaces, which are specifically designed to let you
address each output of a Matrox or DataPath X4 individually, so you can do
anything with them that you could with two directly connected displays. The
added benefit is that they’re from one output, so they’ll always be
perfectly frame-synced.

Do you have any suggestions as some good economical devices (brands and
> models) that will work well.  I have borrowed and tried a variety of
> cheaper usb to video adaptors with varying success.  My current projectors
> don't have HDMI in but my next pair probably will.
>
USB video adapters are not real graphics cards, and are not supported for
use with QLab. They are not capable of supporting some of the graphics
technologies built into OS X that QLab requires for much of it’s advanced
video functionality, in addition to just generally being known to be
buggy*, and using a lot of CPU and USB bandwidth.

If your iMac doesn’t have two built in video outputs, a Matrox or DataPath
is going to be your only option, although how well it will work on your
iMac will depend on the particular specs of that Mac.

How much video you can get away with pushing out of an iMac (or any Mac)
depends a lot on its graphics card. If it’s only got an integrated graphics
processor, which shares regular RAM instead of having dedicated (and
faster) video memory, it’s going to be a lot less capable than one with a
dedicated NVIDIA or AMD card with vRAM.

What an integrated GPU can handle depends on the total resolution of all
the displays, as well as exactly what you’re doing. Straightforward
playback of one video at a time may not be a problem, but once you’re
layering, fading, edge-blending, etc, that’s going to show the limits of
the integrated GPU quickly, especially on a six-year old model.

(Even with current models, only certain 27” iMacs have dedicated graphics
cards. All 21”, and the lower end 27” models, have integrated graphics, as
do all Mac Mini models, all 13” and smaller MacBook Pro models, all non-Pro
MacBook models, and the lower end 15” Retina MacBook Pros. For more than
entry level video projection, you are limited to certain 27” iMacs, certain
15” rMBPs, or Mac Pros.)

Hope that helps, although I know it’s not the answer you were hoping for!

-Andy

—
Andy Lang
@SoundGuyAndy <http://twitter.com/SoundGuyAndy>
support at figure53.com
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