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How much delay can I expect with this setup?
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Rehan  
#1 Posted : Sunday, December 29, 2013 10:21:02 AM(UTC)
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Hi, everyone. I'm designing an upgrade to the live video system in our building from SD to HD, and I'm looking at both vMix and Blackmagic Design ATEM switchers as options. I like the functionality (and the cost) of vMix, but it won't be suitable for us if the delay is too much.

As inputs, we will have a laptop plus a 1080p PTZ camera (Sony SRG-300H). I know a camera with HD-SDI output would be preferable, but I don't have the budget for that.

Here's the proposed layout of the system:

UserPostedImage

For the laptop input, I already have an AVerMedia Live Gamer HD capture card. The delay from the laptop is not important.

For the camera input, I have not yet purchased a capture card. And I don't have a second graphics card for external output, either. So I was thinking that I would use a Decklink SDI card, and attach a Blackmagic Design HDMI-to-SDI converter to the camera.

On the TV side, I plan to use SDI-to-HDMI converters that have about 1 frame delay (based on the review at http://vimeo.com/51770361 ... I will be testing one for myself soon).

So my question is: How much delay can I expect from this layout, and what can I do to minimize the delay? Is there a better option than the Decklink SDI card to capture the camera input?

Thanks.
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davesuemcbride  
#2 Posted : Monday, December 30, 2013 2:40:54 PM(UTC)
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Just from a quick look, looks like the PTZ camera outputs HDMI - is there a distance factor that makes SDI necessary? Might be able to save a frame or so by going HDMI direct into the capture card?

I think the vMix delay is minimal at just a frame or two, but I'll let the experts be more specific on that ;)
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wwdv  
#3 Posted : Monday, December 30, 2013 3:11:04 PM(UTC)
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Hardware converters don't have a noticeable delay.
vMix has a delay that can vary from 50-200ms.
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Rehan  
#4 Posted : Tuesday, December 31, 2013 5:10:54 AM(UTC)
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davesuemcbride wrote:
Just from a quick look, looks like the PTZ camera outputs HDMI - is there a distance factor that makes SDI necessary? Might be able to save a frame or so by going HDMI direct into the capture card?

The reason for converting the camera's HDMI output to SDI is that SDI is recommended at http://www.vmix.com.au/k...e/article.aspx/3/latency and I've read that the BMD HDMI-to-SDI converter has very minimal delay -- about 1 line.

I tested the HDMI output of my laptop directly into the HDMI capture card, and it seemed to be 3-4 frames delay between the laptop screen and the vMix screen. That was using the "Capture Low Latency" option.
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wwdv  
#5 Posted : Tuesday, December 31, 2013 9:21:25 AM(UTC)
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I think, vMix is using some kind of a buffer for processing, in my case the preview screens have already a delay of 5 frames (composite video sources).
The output on my beamer has no extra added delay.
A faster computer will decrease the delay I suppose.
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admin  
#6 Posted : Tuesday, December 31, 2013 10:11:34 AM(UTC)
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wwdv wrote:
I think, vMix is using some kind of a buffer for processing, in my case the preview screens have already a delay of 5 frames (composite video sources).


vMix only adds a very small amount of delay, less than 2 frames.
You will find these extra delays are due to the deinterlacing processing that is done on some capture cards (such as the Osprey Analog cards)
You can have a look through the Osprey settings to see if this can be reduced.

(Through Input Settings -> Advanced, select Osprey then click Properties)
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wwdv  
#7 Posted : Tuesday, December 31, 2013 11:08:24 AM(UTC)
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The preview (videocheck) of the Osprey 440 shows no delay and the deinterlacing process has already taken place in this preview.
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admin  
#8 Posted : Tuesday, December 31, 2013 11:26:54 AM(UTC)
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Then it is difficult to say where the delay is happening.
vMix only has two buffers maximum, so it is impossible for it to hold 5 frames on its own.
Maybe the osprey card is buffering further before sending to vMix.

You can see the buffer size in vMix by going to the Statistics window (coloured bar button in bottom right hand corner of vMix)
In the Video column the number in brackets is the delay in milliseconds, this usually around 40ms or approximately 1 frame.

Regards,

Martin
vMix
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wwdv  
#9 Posted : Tuesday, December 31, 2013 12:45:36 PM(UTC)
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All 4 inputs shows arround 40ms.
I can try to turn of the built-in deinterlacing (adaptive motion) and use vMix deinterlacing.
Is it as good as the built-in one?
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admin  
#10 Posted : Tuesday, December 31, 2013 9:21:58 PM(UTC)
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Adaptive motion is the best quality but it introduces a lot of latency.
You disable it and use vMix deinterlacing at slightly less quality.
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wwdv  
#11 Posted : Sunday, January 19, 2014 10:24:31 AM(UTC)
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If I buy a IP camera that supports rtsp and connect it via stream input (local network).
Can I then expect a smaller delay then 200ms?
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admin  
#12 Posted : Sunday, January 19, 2014 10:27:57 AM(UTC)
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The shortest delay I have seen is with an SDI capable camera and capture card.
(2.5 frames from camera to screen)

IP cameras will always have a higher delay due to the H264 compression.

Regards,

Martin
vMix
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