Low latency graphic overlays over mutlicast/unicast streams


We are working on a project where we would like to overlay interactive graphics (triggered by 3rd party system) over multicast (or unicast) h.264 (or h.265) streams and then show the streams on monitors/screens.

Do you have any experience with such a setup, and what are the latencies we can expect?

  • mainly due to the latency introduced by decoding of streams, but also in respect to the type of delivery of the steams to the screens:
  • unicast/multicast (+ decoding by some tool like FFPLAY and playing it on the screen)
  • NDI
  • SDI/HDMI over some interface card

The cameras that produce streams can keep the latency as low as 7ms. We would like to reduce the latency introduced by Caspar as low as possible.


Do everything with SDI, key CCG over your cameras on an actual video switcher. Take the switcher output and do your multicast with http://www.ultragrid.cz/ (and you can use that as a player also).

You should be able to get ~2-4 frame latency.

Thanks for the suggestion @hreinnbeck
Unfortunately, the cameras can only produce multicast or unicast h.264/h.265, so I can’t use SDI for input.
That is why I wonder about the latency introduced by CasparCG when decoding the streams from cameras?
Once the streams are decoded and graphics overlayed, I can output to SDI or NDI since it should also be low latency.

Then you should just use OBS.

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Or you can use VLC to decode the streams and send the result via NDI to Caspar (using the VLC NDI Plugin). Then use a Decklink to output to SDI or HDMI for the monitors.

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