logo

Live Production Software Forums


Welcome Guest! To enable all features please Login or Register.

Notification

Icon
Error

Options
Go to last post Go to first unread
JW  
#1 Posted : Sunday, July 16, 2017 6:40:07 AM(UTC)
JW

Rank: Advanced Member

Groups: Registered
Joined: 6/25/2017(UTC)
Posts: 30

Thanks: 5 times
Was thanked: 6 time(s) in 5 post(s)
We will replace our old analog PTZ camera's in our church later this year.
I had SDI or HDMI camera's in mind, but the new NDI camera's looks very promising.
Because live playback (without noticeable delay) is very important for us I've got a few questions:

Is the latency of a NDI camera in vMix always smaller than a SDI/HDMI camera including the latency of a SDI/HDMI capture card?
(are there no buffers used that can increase the latency when the network might be overloaded sometimes?)

Has SDI less latency than HDMI?

What is the best way to send the vMix output to a beamer (150ft away) with minimum latency:
HDMI over cat5e or NDI (vMix NDI output) to HDMI with a converter?

(I assume there are no NDI beamers yet)
DWAM  
#2 Posted : Sunday, July 16, 2017 9:47:46 AM(UTC)
DWAM

Rank: Advanced Member

Groups: Registered
Joined: 3/20/2014(UTC)
Posts: 2,121
Man
France
Location: Bordeaux, France

Thanks: 149 times
Was thanked: 602 time(s) in 468 post(s)
In terms of latency, I would say SDI is best, then HDMI, then NDI. At the moment it's impossible to say if a NDI camera will improve this.

When feeding a beamer, HDMI over cat5e or NDI (vMix NDI output) to HDMI with a converter?
I guess this will give pretty much the same result as most of the latency is created by vMix going to the HDMI or NDI output
kane  
#3 Posted : Sunday, July 16, 2017 9:58:29 PM(UTC)
kane

Rank: Advanced Member

Groups: Registered
Joined: 3/24/2016(UTC)
Posts: 326
Location: Chicago, IL

Was thanked: 138 time(s) in 92 post(s)
There is so much more to this than just the type of cable, which probably makes little difference in the grand scheme.

What really does matter are things like video format, frame rate, video scan type, the type of cameras, projector and the entire video chain when it comes to what you total latency will be. Its not a single device, but all of them added together. If you just slap together a bunch of parts hoping that latency will be low, it will most likely not be.

Getting low latency takes work, testing, possibly changing out gear and making some compromises. Beyond that, if this is a very large venue, you aren't going to be able to get perfect a/v sync everywhere, because light and sound travel at such different speeds from each other. At 30fps, sound travels about 11 meters (37 feet) per video frame. For example, say you are in a large venue with perfect a/v sync output, and you are 150 feet from the screen/speakers you are dealing with a 4 frame a/v sync that all caused by physics. Where as people directly in front of the screen will have no a/v sync issues.

Here are a few things that I could recommend.

1. Work progressive, no interlace video formats!
2. Work in the highest frame rate possible, if you can't do 1080p60, then do 720p60.
3. Don't convert between video formats (use the same frame rate and resolution everywhere).
4. Don't externally change between cables types (like digital to analog, HDMI to SDI, etc).
5. Some cameras have latency from lens to output, turn off any processing in the camera (like image stabilization).
6. The output device is usually the highest latency device in most setups. Find out what the native resolution of the output device (projector) and work in the video format. If your projector doesn't work in a native video resolution (720 or 1080p) think about replacing it with one that does.
7. Turn off all image processing in your output device (keystone adjustment is a big no!)
8. Use genlock
9. Disable the input frame syncs (you can do this on a TriCaster, can it be done on a vMix input card?)

All of these ideas are just recommendations, and you would need to test your specific setup to see which ones matter. In some cases, you might find a different answer than what I'm recommending.

Most people would say that 3 frames (100ms) or less of latency can't be noticed by the average person and 6 frames (200ms) or less would probably be acceptable to most people. By average people, I mean your typical person off the street, not a video professional that will agonize over every frame they can measure.

Can NDI be used? Possibly. It's typically a frame or less to convert from a baseband video sources into NDI. But again, this is all additive. For some configurations that extra frame will not be a problem, but in some video chains, you will be working to get back each and every frame of latency you possibly can. On the flip side, going NDI to a computer outputting at the native resolution of your projector might improve things versus using an input that isn't native resolution.

Finally, I'm not a vMix expert, there might be other things I'm not aware of with this system. The above is what I would tell a TriCaster user.

Kane Peterson
NewTek
thanks 4 users thanked kane for this useful post.
JW on 7/17/2017(UTC), boris9831 on 7/19/2017(UTC), mjgraves on 8/9/2017(UTC), Barney Box Lane on 12/31/2018(UTC)
boris9831  
#4 Posted : Wednesday, July 19, 2017 4:42:28 PM(UTC)
boris9831

Rank: Advanced Member

Groups: Registered
Joined: 10/21/2016(UTC)
Posts: 48

Thanks: 21 times
Was thanked: 4 time(s) in 4 post(s)
Thanks Kane. Very thorough and helpful. BTW - in the USA a beamer is usually a "term" for a BMW automobile. So when I saw the title I was really curious how to use vMix in an automobile. :-) So - in video terms we call a beamer a projector.
JW  
#5 Posted : Saturday, July 22, 2017 1:49:19 PM(UTC)
JW

Rank: Advanced Member

Groups: Registered
Joined: 6/25/2017(UTC)
Posts: 30

Thanks: 5 times
Was thanked: 6 time(s) in 5 post(s)
boris9831 wrote:
Thanks Kane. Very thorough and helpful. BTW - in the USA a beamer is usually a "term" for a BMW automobile. So when I saw the title I was really curious how to use vMix in an automobile. :-) So - in video terms we call a beamer a projector.



I have modified the title, now the whole USA understands what I mean. :)
Ronald555  
#6 Posted : Thursday, December 27, 2018 1:57:12 AM(UTC)
Ronald555

Rank: Advanced Member

Groups: Registered
Joined: 1/25/2018(UTC)
Posts: 41

Thanks: 10 times
Was thanked: 2 time(s) in 2 post(s)
Originally Posted by: kane Go to Quoted Post

On the flip side, going NDI to a computer outputting at the native resolution of your projector might improve things versus using an input that isn't native resolution.



I'm curious if there are any NDI|HX camera users that have experienced this.
(NDI|HX has some more latency, but you are also skipping a few (capture card) steps)
Users browsing this topic
Forum Jump  
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.