Real-time playout performance

General
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1

Hi,

I’m using CasparCG Server in a Linux environment (Ubuntu 16.04) to create a live video playout. I’m using a BlackMagic DeckLink Quad Card and configured the SDI to half-duplex, so that I have 6 inputs and 2 outputs. The outputs have a delay of approximately 0.6 seconds. I was wondering if it is possible to decrease the delay? How can I get my output as real-time as possible?

I found this video https://www.youtube.com/watch?v=LolRTtVAgHw which claims to have a delay of 1 frame using internal keyer. But since I’m using half-duplex I won’t be able to use the internal keyer.

I am using CasparCG Server 2.1.0.472 dc2e94b Beta 2 with a NVIDIA GeForce GTX 1080 Ti as GPU.

Cheers, Marco

2

The frames never leave the Decklink using the internal keyer so achieving 1 frame is possible. You can change the decklink settings in the config, setting latency to low and experimenting with buffer-depth. However you will always have X frames of delay.

3

Thanks for your quick response!
I already configured my config to use low latency and set a buffer-depth of 3. This is what my config looks like:

<channel>
<video-mode>1080i5000</video-mode>
<consumers>
<decklink>
<device>8</device>
<embedded-audio>true</embedded-audio>
<latency>low</latency>
<buffer-depth>3</buffer-depth>
</decklink>
</consumers>
</channel>

I’m not expecting a 1 frame delay, but 0.6 seconds is way more than I expect it to be. Are there any other settings which will make the delay lower?

4

You play the Decklink inputs on your output, right? Did you add some de-interlaceing setting to your play command? Because I would expect 6 or 7 frames of delay and not 15 (0.6s).

5

Yes I play my Decklink inputs on the outputs.
I didn’t use a deinterlacing so far. Looks like the deinterlacing decreased the output delay, if have a delay of 0.4sec at the moment. Thanks for the tip!

6

Funny, I had a delay of multiple seconds with the deinterlaceing added, I wanted to warn you and make sure, that you did not add it. But that seems to do different things on different systems :slight_smile: