I have a 16 port pv-981 with 4 bt878 chips. I'm looking at increasing the number of cameras I have but I currently have 5 cameras and the bt878 chip that shares two cameras gets combing unless I set the zoneminder config flag to throw away one frame after switching channels and before capturing an image. This has reduced the frame rate to about 2.5fps (about 6fps without the option). This is getting into the unacceptable area for me. If I need to add 3-5 more cameras I'll be double on all chips or three for one chip.
I'm wondering now if anyone would ever recommend a 16 port card because the framerate is so terrible when using more than 1 channel?
And last, do most people get combing of images when using multiple channels or does it have more to do with specific combinations of different models of cameras being used on the same chip? Combing for me only shows up on one camera at a time and it switches back and forth every few minutes as to which one has the combing. One camera is native 480i the other is 420i but I have them both recording to 480i, switching to 480i and 420i has no effect.
16 port cards worthless?
Yes the combing is due to using multiple channels on one chip. When using more than one channel on a single chip, Zoneminder will do a cycle where it will change the channel and grab the capture image and then change the channel can grab the capture image. The combing artifacts are caused by the channel changing on the capture chip. The first frame the capture card captures isn't necessarily going to be a clean image. Think of it like changing channels on a television set it takes about a second for the picture to become stable. This is you need to set ZM_CAPTURES_PER_FRAME frame to 2 to address the problem. That makes Zoneminder skip the first frame the capture chip captures right after a channel change.
These are to options you have:
1) Capture at full resolution (640x480 for NTCS) and live with the combing. If you have sensitive motion detection, the combing will set of false alarms when the combing flickers.
2) Capture at full resolution with ZM_CAPTURES_PER_FRAME set to 2 and live with the slow frame rates.
3) Capture at half resolution (320x240 for NTCS). The combing goes away when capturing at half resolution, but sometimes the image shake up and down for one pixel's distance.. I never tried this option for a long time. I don't know if the shaking will set off motion detection or not.
I have a PV-155 (16 ports, 4 capture chips) and eight cameras using ZM_CAPTURES_PER_FRAME=2. I'm okay with the low framerates. 2.5 isn't great but good enough for most needs. I have 3 cameras on 1 chip that are running at ~1.6 fps each. 1.6 fps is a little low but it works.
Do I think a 16 port, 4capture chip card worth it? Yes I do. They are not that much more expensive than a for port card (at least in the case of the Pro Video cards you get from bluecherry). I wouldn't use all 16 ports, but in my case, 2.5fps on some cameras and 1.6 fps on some works for me. It's alot better than using the 16 port card with my 8 cameras than having to buy two 4 port cards. I would however warn people about the banding and the low frame rates when you use more than one camera on a single capture chip.
These are to options you have:
1) Capture at full resolution (640x480 for NTCS) and live with the combing. If you have sensitive motion detection, the combing will set of false alarms when the combing flickers.
2) Capture at full resolution with ZM_CAPTURES_PER_FRAME set to 2 and live with the slow frame rates.
3) Capture at half resolution (320x240 for NTCS). The combing goes away when capturing at half resolution, but sometimes the image shake up and down for one pixel's distance.. I never tried this option for a long time. I don't know if the shaking will set off motion detection or not.
I have a PV-155 (16 ports, 4 capture chips) and eight cameras using ZM_CAPTURES_PER_FRAME=2. I'm okay with the low framerates. 2.5 isn't great but good enough for most needs. I have 3 cameras on 1 chip that are running at ~1.6 fps each. 1.6 fps is a little low but it works.
Do I think a 16 port, 4capture chip card worth it? Yes I do. They are not that much more expensive than a for port card (at least in the case of the Pro Video cards you get from bluecherry). I wouldn't use all 16 ports, but in my case, 2.5fps on some cameras and 1.6 fps on some works for me. It's alot better than using the 16 port card with my 8 cameras than having to buy two 4 port cards. I would however warn people about the banding and the low frame rates when you use more than one camera on a single capture chip.
Interlacing is a standard part of analogue video signals (PAL/SECAM/NTSC as used for TV, CCTV, etc.), so if you're using a standard video input and a video capture card, and you go for a larger frame, then you'll get a interlaced image.The cut-in points are at vertical resolutions greater than 240 for NTSC and 288 for PAL.
This is no surprise to us. You are stacking lots of known compromises, and are surprised by the poor output?
1) Analog video is interlaced. That means each frame only has half the horizontal lines. This causes combing. It is worse in a split chip because you no longer have the 2 adjacent frames. Capture at 1/2 resolution to get clean signal.
2) A bt878 chip captures at 30fps. Switching channels takes time. The more you split, the more you loose. Split less for better rates.
3) You can have a max of 16 bt878 chips in a single system. Try the PV183-16 for a 2 way split, or 2 PV183-8's for direct chip to stream capture.
In many of my systems I have a 8 port 8 chip card and a second split chip card (1-4 or 4-16 or 8-16) which runs at 320x240 and a lower frame rate.
Pick the proper tool for the job. There are good jobs for 4 chip 16 port cards... Just not all jobs.
1) Analog video is interlaced. That means each frame only has half the horizontal lines. This causes combing. It is worse in a split chip because you no longer have the 2 adjacent frames. Capture at 1/2 resolution to get clean signal.
2) A bt878 chip captures at 30fps. Switching channels takes time. The more you split, the more you loose. Split less for better rates.
3) You can have a max of 16 bt878 chips in a single system. Try the PV183-16 for a 2 way split, or 2 PV183-8's for direct chip to stream capture.
In many of my systems I have a 8 port 8 chip card and a second split chip card (1-4 or 4-16 or 8-16) which runs at 320x240 and a lower frame rate.
Pick the proper tool for the job. There are good jobs for 4 chip 16 port cards... Just not all jobs.