Solstace Posted November 24, 2009 Share Posted November 24, 2009 Mornin' all! I run a video system that currently takes 1080i in from a laptop (long story but that resolution likely won't change anytime soon), and we then key live content from our PAL (SD) cameras through that laptop output before distributing the 1080i output signal via HDMI to a range of Plasma and projector-based displays. The end result looks "good enough" for our current use and expectations, but there is a small delay which I guess is due to the keyer/switcher/scaler unit having to sync the camera input to the laptop input. This delay can be a distraction if the speaker makes a lot of fast and wide gesticulations! Our cameras are sync'ed together with a black-burst generator, and this got me thinking... Is there a way of using the laptop's 1080i DVI output to generate a stable clock suitable for frame-syncing the cameras? Or is there a graphics card on the market that can accept a frame-sync input for this kind of live video application? I guess if we applied such a solution we would still have to wait for the analogue to digital conversion, but at least then the keyer/switcher/scaler box doesn't then have to sync things up as well! One way around our present situation I guess could be to use our keyer/switcher/scaler box in a mode that has a feed from our black-burst generator input to set its external (and therefore working sync resolution) to. But we then lose resolution on our text output which does rather seem to affect readability. I guess too that this would further degrade given the interlacing that would be applied on top, so we've discounted that option entirely even if it could be technically feasible. My Google-fu didn't seem to throw up any obviously useful answers this morning, so thought I'd ask here. Thoughts anyone? Link to comment Share on other sites More sharing options...
TonyC Posted November 24, 2009 Share Posted November 24, 2009 I know you said you completely discounted this option but what you need is a Grass Valley Indigo with a high res board, allows you to mix and output between HD and SD inputs and can be used as a sync generator or be included in the setup you already have. There not cheap mind you, but you pay for what you get. Link to comment Share on other sites More sharing options...
Phill Power Posted November 24, 2009 Share Posted November 24, 2009 Have you tried running your laptops & keyer/switcher/scaler box at 75Hz? (if they will) Link to comment Share on other sites More sharing options...
mac.calder Posted November 24, 2009 Share Posted November 24, 2009 I know you said you completely discounted this option but what you need is a Grass Valley Indigo with a high res board, allows you to mix and output between HD and SD inputs and can be used as a sync generator or be included in the setup you already have. There not cheap mind you, but you pay for what you get. You will still have issues with the indigo... Any scaling will add a frame or two in delay, the keying will add another frame or two. It is a fact of life I am affraid. That said, SDI scaling is often slightly faster - if your cameras are capable of SDI out, and your mixer capable of SDI in, maybe this is a solution. Another is to delay your audio by a few milliseconds. This can often bridge the eye-ear divide in a large room, but often does not work in a small room. One option (not cheap) which may be slightly more efficient would be to get an HD-SDI output card for your PC which can be genlocked on the output. You can still output 1080i and you will be fully framesynched from the get-go. Link to comment Share on other sites More sharing options...
sleepytom Posted November 24, 2009 Share Posted November 24, 2009 Nvidia Quadro cards can be ordered with external sync (trilevel or burst) - they cost about £4000 with sync in and sdi out though so its generally considered to not be worth it unless you have stereo 3d setups which require syncronised outputs. which keyer/switcher/scaler box are you using? some of them have much more delay than others. Are you running all your displays at native resolution (ie are they all 1080i native?) if they are not then you'll get additional delay in the display scaler. Link to comment Share on other sites More sharing options...
lobba Posted November 24, 2009 Share Posted November 24, 2009 It sounds like you want to genlock and time your Laptop DVI output. NVIDIA offer desktop workstation cards with genlock that are very expensive, a more cost effective option would be something like this.... http://www.matrox.com/video/media/pdf/prod...i_datasheet.pdf There are lots of these around by all your favourite AV manufacturers! the 1080i on DVI may be the biggest problem. I don't know what switcher/scaler/keying box you are using but a lot of data switchers that will even look at an interlaced DVI signal will deinterlace it at the cost a a frame/frame and a half before adding any processing delay on top and then re-interlace on the output. You might reduce the delay by turning your source signal progressive without it costing you too much. Oh and I just want to check, when you say you are keying the SDI feeds 'through' the laptop output, you aren't capturing the sdi feed into the laptop and keying internally are you? You are using a switcher that is doing some sort of key and fill? Lobba Link to comment Share on other sites More sharing options...
J Pearce Posted November 25, 2009 Share Posted November 25, 2009 Don't forget a lot of that delay may well be in the projectors and screens. It is worth disabling any disable-able onboard processing that you don't need/use. Link to comment Share on other sites More sharing options...
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