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VMix to Projector Via SDI/BM Decklink - Lagging Issues
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Joined: 1/1/2019(UTC) Posts: 8  Location: Port Huron Thanks: 4 times
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We have our VMix PC setup with a Blackmagic Decklink Video Output (SDI) that is hooked directly into our Epson Projector. The total distance between the PC and Decklink is about 50 feet. Our cameras are all PTZOptics NDI 30X zoom cams (3) with a single PTZ Z-Cam also. We're projecting the Vmix output to the projector via External 2. Problem is that there is about a full second delay between the speaker on the stage and the screen behind him.
We've reviewed and tested just about every setting we can think of in the Decklink software and cameras. VMix software doesn't appear to have any settings relative to this issue that we could readily find.
Does anyone have any clue on what we may have overlooked?
thanks in advance for any help on this.
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 1 user thanked douglukas for this useful post.
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Joined: 8/5/2017(UTC) Posts: 569  Location: Manitoba Thanks: 113 times
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Unfortunately, any software switcher will have a certain amount of delay. There is also some delay in the PTZOptics cameras themselves. I have 4 of them and usually use them with NDI ,but only for streaming or recording events (not for feeding projectors). I noticed that even the SDI Outputs on those cameras have some delay. It's probably not what you want to hear, but it's a reality we live with... If a software switcher is your only option then you will always have some amount of delay. Ideally you should use a hardware switcher for iMag projections to 'minimize' delay issues.
The Decklinks and cameras are likely the least of your worries when it comes to delay. Although 1 second in your setup seems a little high, it's not impossible if you add up all the delays in the signal path.
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1 user thanked raugert for this useful post.
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Joined: 1/1/2019(UTC) Posts: 8 Location: Port Huron Thanks: 4 times
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Thanks for the quick reply. I think at the end of the day, you are absolutely right. We pretty much attempted to optimize all settings and the best we can get is about a 1/2 second delay. Nowhere near acceptable. Thanks for the input.
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Much of the delay you experience is caused by the NDI cameras. They leverage NDI-HX which is basically form of H264 encoding. It has considerable delay built-in.
If you run SDI form the cameras into your vmix system this would be eliminated. Or use an external NDI encoder like the ones from BirdDog, to get the signal from the camera onto the network. Full NDI (not HX) does not introduce that delay.
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We have a vMixGO system and we send our projector feeds out using the 'Fullscreen' option instead of the External Outputs. Doing so reduced the latency by about half a second. I don't know if your PC setup has a similar function but if it does you might give it a try.
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VMix to Projector Via SDI/BM Decklink - Lagging Issues
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