Can Someone Explain? (Tech Question)

tbh

Mods - not sure where to ask this, so obviously please move if needs be.

last night, when I was watching the France - Spain game, that, if a player went to take a throw, for example, it would appear on the big screen at the ground about a second after I saw it on TV. Is this an optical illusion, or does the picture get to my TV before it gets to the big screen? Anyone know?

cheers,
tbh

Smellyirishman

Camera -> TV at ground = small enough delay (say 1-2 seconds)
Camera -> TV at your house = Far bigger delay

It's pretty hard to explain (or at least I am finding it hard to) but when you think about it, you see the delay on the big screen because that is what's happening, the image you get from the stadium is an instantaneous one of both the big screen (if it is in the shot) and the match so it catches the delay too. You do not however see the actual match, or even the big screen footage before the people in the stadium.

Someone will be along shortly to explain it better!

tbh

Smellyirishman wrote:

Camera -> TV at ground = small enough delay (say 1-2 second)
Camera -> TV at your house = Far bigger delay

It's pretty hard to explain (or at least I am finding it hard to) but when you think about it, you see the delay on the big screen because that is what's happening. You do not however see the actual match, or even the big screen footage before the people in the stadium.

Someone will be along shortly to explain it better!

I think I know what you are saying - basically, I see the throw, and the delay, but in fact both of them have already happened by the time I see them, is that it?

loyatemu

thats a reasonable explanation but it doesn't explain why there would be a delay on the big screen in the first place - electrical signals travel at the speed of light. Unless the signals from the cameras were being beamed by satellite to be vision-mixed elsewhere and then sent back to the stadium for the big screen (possible, but seems unlikely)

Smellyirishman

Yep.

What you see on your screen happened at the same time(IE the player throwing the ball on the pitch, but only preparing to throw it on the big screen). It's just because of the delay between the camera and big screen in the grounds that it looks off.

Smellyirishman

I don't know how TV recordings really work, but there may be some sort of post-processing done to the images caught on the camera ,Compression maybe or some sort of editing team stuff, that would delay things. Also, since the signal only travels as fast as the medium it passes through allows, I think TV signals are sent at between 60-90% the speed of light as they use Coax cables, or a varient of them. They may use some sort of fiber but again I am not sure.

FlutterinBantam

Could be that sure enough.......by any chance is your screen at home bigger than the big screen at the stadium?

Highly unlikely i know but...........;)

tbh

no boss, I've an 8 inch black and white Pye model - it does me!

Mossy Monk

would it take longer for the HDTV to be processed for the big screen?

stereo_steve

Surely TV is compressed in real time? If for arguments sake if it took even 1.1secs to encode 1 sec of TV, their would be constant interuptions in transmission.

Smellyirishman

All I know for sure is that there is a delay, the reasons for which I am not entirly sure (Although I think lag and my next one may be close). Another reason could be that a buffer needs to be filled first before the feed can continue and that is the reason for the delay.

byte

Anyone that's been to concerts with big screens will possibly notice the same delays. The screen could be a second or so out with the stage.

At least, it did for me at Slane one year

Smellyirishman

Yes, but why? Why damn it, WHY!!

..I guess I will just have to accept my own explainations, who knows, they may even be correct!

byte

A buffer is plausible alright.

kevmy

There are ~ 20 cameras looking at the pitch (and just the pitch not the crowd) and the pictures all come into a control room in the bowels of the stadium ~ instanteous. The delay is then caused by the editor deciding which camera to use ie. close up of Beckham or behind the goals or close up of goalie etc. These pictures are then sent to all TV stations and the big screen in the stadium (this is why all TV pictures RTE, UTV, BBC are all the same). It can also be used to protect the ref by not showing controversial ref decisions in the stadium.

On a related note the delay between RTE and UK stations is because the pictures make two round trips to the satellites in space for UK pictures to get here but only one trip for RTE. This is why RTE is always ~2 secs ahead for soccer matchs overseas.

Telefís

The vision mixer or director deciding what shots to call is not the reason for the delay on the big screen; regardless of when the decision to cut is made, a cut still takes place and there is still a delay to the screen relative to that cut!

I don't know what the reason is either, other than to suggest that perhaps the sheer scale of these screens is such as to make covering their vast areas with information so quickly a practical impossiblity, so there is an element of delay in the data reaching all parts of the screen before it becomes fully active.
A theory.

John R

Telef&#237 wrote: »

The vision mixer or director deciding what shots to call is not the reason for the delay on the big screen; regardless of when the decision to cut is made, a cut still takes place and there is still a delay to the screen relative to that cut!

I don't know what the reason is either, other than to suggest that perhaps the sheer scale of these screens is such as to make covering their vast areas with information so quickly a practical impossiblity, so there is an element of delay in the data reaching all parts of the screen before it becomes fully active.
A theory.

I wouldn't have thought so, I have seen bigger screens at concerts which didn't have any delay.

In the end it is just a square of coloured lights, they are not usually any higher resolution than a tv, just much bigger points of light.

Possibly there is no direct link to the screen and they just take it off the satellite feed like everyone else.

Telefís

Quite possible. In fact, given the crowd in the stadium, it's entirely possible that it is German television ARD's feed going to these monitors from their HQ in Berlin.

So the clean feed from the control room at the stadium is routed over to ARD, who in turn add their graphics etc, and then feed it back to the stadium, hence the delay...

godtabh

If you look at the RTE broadcast and the ITV/BBC broadcast there is a delay in there coverage of the same match. Whats going on there?

Or is that the same thing

Smellyirishman

Please refer to post #15 p.2

godtabh

Smellyirishman wrote:

Please refer to post #15 p.2

Sorry missed that. Thanks

kevmy

Telef&#237 wrote: »

Quite possible. In fact, given the crowd in the stadium, it's entirely possible that it is German television ARD's feed going to these monitors from their HQ in Berlin.

So the clean feed from the control room at the stadium is routed over to ARD, who in turn add their graphics etc, and then feed it back to the stadium, hence the delay...

That could it too. I was only guessing with my previous post.

Definetly not delay in cables as speed of light = 3x10^8 m/s so even at ~60%
that would still be 2x10^8 m/s. That means 20,000 km of cable to give a one sec delay. Its either at one end or the other.

Dustaz

Not sure if it helps in any way, but most pieces of digital equipment that a video signal passes through add a one frame (1/25th of a second) delay. I guess its possibly that there are 25 such pieces of equipment (but i doubt it) between the desk and the screen in the stadium (if the screen is getting a live feed)