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Extra delay while enabling multiple capture cards

Rogier Tuinte

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Hello all,


I'm just wondering...

Our Watchout system works perfect. Inside the players we've multiple capture cards. BMD Intensity Pro, BMD Decklink SDI, Datapath Vision RGB Pro.

I want to upgrade the systems with the VisionRGB-E2 capture cards.


The delay while capturing only live video with the SDI capture card is acceptable. In the past we did some tests with adding color effects / tween tracks to the live video input. Overlay the live video with logo's, etc. This resulted in a extra delay.


For a upcoming project I've to show live video (SDI input) and computer graphics (Vision RGB input) at the same time.

Do I get extra delay when I capture the computer graphics at the same time with the live video feed? Without using effects and similar.


I'd like to have a discussion about what's important to consider while capturing live inputs in combination with:

- Color effects and other tween tracks.

- Picture in picture borders with transparency

- Overlay other media elements

- Etc, etc.

How does Watchout process live inputs?


It seems to me that capturing analog video signals from a camera results in more delay then capturing a SDI signal from the same camera. Because of the conversion from analog to digital. Am I correct?


Something else i noticed is that the SDI or HDMI output of a capture card is disabled as long as there are no cue's on the timeline. As soon as I trigger a live feed Que. Watchout or the capture card driver enables the output of the capture card.

I want to use the outputs for the preview monitors. Now I've to trigger the live feed and play with the opacity during the presentation, so that the output is always active.


The output is also useful for linking the capture cards output from one display machine to the capture cards input from another display computer. In this case no need for a SDI or HDMI splitter.

But this only works when the live feed is active in Watchout.

Beside this I don't know if there is a small delay between the input and output of a capture card or if the signal is routed directly to the output without any processing / delay.


Kind regards


Rogier Tuinte

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  • 2 weeks later...
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In regards to "looping" your cards together SDI for "ease" of setup... I would avoid this.


You are potentially introducing frame delay between the inputs by varying the travel length the signal has to move before hitting another card.


Single source>cable>DA>identical cables>capture card is how I would do this.


Instead of this:

Single source>cable>card>cable>card>cable>card


Signal travels VERY fast for sure... but going back to old 5-wire RGBHV/VGA days for a bad example: If your red cable was shorter than the rest you would get "ghosting". The red signal would arrive ahead of the green and blue and sync and the processing would show this. Really there are more physics involved than that... like red travels faster than blue and green naturally anyway but that's all analog issues and beyond this example.


Yes, you are dealing with digital vs analog with SDI so you won't see color shifts like that but I believe you are running the risk of having sync issues if you have an input that crosses Displays between multiple servers. Your sync is hitting card 1 which starts its capture, then loops out to card 2, which then starts its capture... If you are on a soft edge blend almost ANY sync issues between Displays/Servers will be noticeable.


Just a thought.


I can't help you with the rest as I only have DVI capture card experience.


Brian Lynn

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