Newbie to Video Projection - But need to get something together quickl

[dosxuk]

VGA may be (generally) simpler - but it IS an inferior technology, it is going to die, and people need to adapt.

Possibly, but seeing the cascade of an HDMI signal being distributed by successive DA's and comparing it with the instant changes in a similarly built VGA system...

 

A proper HDMI distribution amp will have delays measured in numbers of samples, which is completely imperceptible. If you're using stuff with multiple frame delays, then you're simply using the wrong kit for the task.

 

As much as I dislike HDMI and it's multitude of pitfalls, latency in the signal chain isn't one of those reasons.

[abbotsmike]

So in a system built incorrectly? Sure, if you treat HDMI like you treat VGA you are going to have a bad time... In this day and age you can do enormous digital video-over-ip matrixes with near-zero (visually imperceptible) switch times covering kilometers that would give VGA system architects a panic attack. But you have to design with the technology.

 

Lack of education and treating it the same as analogue audio is why people have issues with digital. Analogue was forgiving*... sure you might loose some pixels here and there, your clocking may skew, the colours might be slightly off, but if close enough was good enough any monkey could patch together a functioning system* that worked most of the time.

 

^{*if you don't care about quality of image and colour accuracy.}

 

Couldn't agree more! I haven't seen a VGA cable in use on an actual job in probably 4-5 years.

 

Use the right kit and design your digital signal chain properly and you'll have no latency issues. Screens are where most latency I see comes in, and most monitors screens that have an appreciable lag have a "game mode" or similar to get rid of most of the processing.

[sunray]

So in a system built incorrectly? Sure, if you treat HDMI like you treat VGA you are going to have a bad time... In this day and age you can do enormous digital video-over-ip matrixes with near-zero (visually imperceptible) switch times covering kilometers that would give VGA system architects a panic attack. But you have to design with the technology.

 

Lack of education and treating it the same as analogue audio is why people have issues with digital. Analogue was forgiving*... sure you might loose some pixels here and there, your clocking may skew, the colours might be slightly off, but if close enough was good enough any monkey could patch together a functioning system* that worked most of the time.

 

^{*if you don't care about quality of image and colour accuracy.}

Now being totally serious here there is an exhibition we do every year with loads of sound and lights, we also used to put in video screens (originally pairs of 19" CRT monitors on 2 sets of distribution) to provide a selection of info screens which started as about a dozen pairs and gradually expanded. One year the organisers removed the video from our remit and another company put up huge advertising banners alongside their 30" 4x3 screens and projector screens but spent the whole of the first day trying to keep the system working.

 

 

Overnight we installed our usual system (our cables have been in the ceiling for many years) for the rest of the week.

Now I know that things have improved over the years but each of the successive companies have failed to install a totally reliable system without having to occassionally reboot something during the 8 day event and none have ever switched images without delay along the system.

 

As a sound guy I'm finding more and more often that I'm expected to add delay to match the video, beit a videowall or multiple screens but I refused point blank this summer to add 1.2 seconds. I'm finding more and more often that such times are becoming very commonplace.

As I said earlier I'm doing a roaring dry hire trade on old technology VGA kit that I never had before when it was state of the art.

 

 

We have never found a problem with colours but we find customers tend to be happier with with a marginally soft image (it it's noticable) compared to glitches and latency.

 

I didn't see there was a page 2.

 

As mentioned I'm a sound guy more than the other genres and certainly have no worthwhile experience with digital video other than plugging it together, I respect and can't argue with those who have.

 

 

So when I see the banks of isomonitors in a digital system, where is the delay? It can't all be blamed on the displays when I see the way the image cascades through with very noticable latency.

Edited November 13, 2019 by sunray

[mac.calder]

Maybe quality of your run of the mil video guys is lower over there, but being unable to keep a video system up for 8 days is endemic of people being employed who don't know what they are doing or are working with poor quality gear. Sure, digital systems can be finicky - especially if you try and cheap out on bit and pieces - but once you get it up, it should be rock solid.

 

We ran a test with Crestron NVX - a video over IP solution. We had 3 x 48 port switches and used Long Range 10G SMoF SFP+'s to send 6 x 4k streams on a 10km loop (SWITCH 1 ->5km SMoF -> SWITCH 2 -> 5km SMoF -> SWITCH 3 ) - and there was 1-2 frames of latency

[ArranAI]

it definitely sounds like either a tech that doesn't know what they are doing or a very badly setup / cutting corners system.

 

I totally agree with the suggestion of 1 or 2 frames latency ( 40 to 80ms ) 1.2 seconds of delay ( nearly 30 frames ) would be completely unacceptable in any video system.

 

mac.calder - please don't take this as representative of us UK video techs... most of us know what we are doing :)

[sunray]

it definitely sounds like either a tech that doesn't know what they are doing or a very badly setup / cutting corners system.

 

I totally agree with the suggestion of 1 or 2 frames latency ( 40 to 80ms ) 1.2 seconds of delay ( nearly 30 frames ) would be completely unacceptable in any video system.

 

 

It may be completely unacceptable to you but I have been asked to add that much and 1/2 second is quite frequent in some very expensive set-ups installed/operated by some well respected companies.

 

 

One only has to watch what's being shown on TV, I'll follow that with even the TV broadcasters can't agree on an acceptable standard of latency between sound and video.

 

I'm sure I only notice the bad systems but there does seem to be a lot of them around.

 

Anyway I'll not get into any arguement about it, I see it's there, I know it exists and I accept that it's state of the art technology. I'm sure it will get better, or perhaps worse if we demand higher and higher resolutions, in time

 

[David Lee]

Sorry VGA died many years ago. If people don't know what they are doing in the digital world then they should probably be elsewhere as it is stable and been around a long time.

[J Pearce]

In jobs where you're running your own cables I'd agree. SDI or HDBaseT or DVI over fibre are all far superior options, not least because of their much better support of EDID and consistency of image on longer cable runs.

 

However, in venues where you're stuck with the house cable runs, VGA can still be a useful option. Older/poorly installed CAT5 that won't support HDBaseT will usually support VGA baluns, older BNC lines that won't support SDI will usually support RGBHV, and many venues have VGA lines pulled and terminated.

VGA does have the advantage of degrading on a poor connection rather than failing, which while not always desirable in image quality will at least get the show up.

 

That said, I've just bought a load of BNC and Cat6, HDMI/SDI converters, and a HDBaseT kit; with a view to abandoning VGA and moving to using venue network and BNC lines for our video setups when we're out and about. The enhanced definition, EDID reliability, and lack of smearing/peak level issues are great advantages of proper digital transmission.

Edited November 14, 2019 by J Pearce