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frame rate with 4xinput on one BT878

Posted: Sun Mar 13, 2005 3:33 pm
by gungner

I can't just get it, if I use one input I can change frame rate, if I use two it seams that it always divide 8 with the amount of active inputs? If I understand this right, the BT878 can handle 25 frames/sec and it gets divided between all inputs. That is, should it not be about 6 and not 2 as I get using all four inputs? All cameras have 10 as maximum frame rate.

cheers, tord

Posted: Mon Mar 14, 2005 2:26 pm
by zoneminder
You have to add in a certain amount of time for the input to be switched and the video re-synced. Expensive cards can do this quickly I believe, so you'll get nearer the 25/n fps you expect, but cheaper cards don't have very good switching circuits so you'll end up getting a lot less performance.


Posted: Mon Mar 14, 2005 4:41 pm
by gungner
that sounds terrable! A card with 4 inputs can only manage 2 frames a second when all cameras are connected? Who wants a card like that? I thought the drawback was just that all settings had to be the same for the cameras, not to end up with 2 f/s. Well one learn all the time.

I just tested with reducing the view to 192x144px and the frame rate increased to a wooping 2.12 f/s :shock: Another strage thing is that when running 4xinputs the picture gets over exposed, why?

cheers, tord

Posted: Mon Mar 14, 2005 9:07 pm
by victor_diago

i can run 4 cameras at about 5 fps each in a 4 input bt878 card

i really dont know why you didnt got same result...

victor diago

Posted: Mon Mar 14, 2005 11:58 pm
by zoneminder
As I said above, it depends on the quality of components and engineering on the card. Cheap cards are slower, I don't think there's any getting away from it :cry:


Posted: Tue Mar 15, 2005 7:05 am
by gungner
Victor, can you please tell me what you have? On my board it's almost just bt878, all inputs goes AC-coupled direct to bt878. I send a link to a picture of my card.

It just cann't be true :cry:

cheers, tord

Posted: Tue Mar 15, 2005 12:52 pm
by lazyleopard
gungner wrote:Another strage thing is that when running 4xinputs the picture gets over exposed, why?
I'd guess there's a problem with the colour/contrast/brightness settings. Another constraint on single-chip boards is that you have to have one set of settings to work for all cameras.