ZoneMinder Forums

Hi Gents,

Odd problem - I have the following capture card:
http://www.math.mcgill.ca/lebaron/rute/ ... 0000000000

I can capture just fine with three monitors running around 9-10 FPS with ZM_CAPTURES_PER_FRAME=0. However, as expected, the three monitors only show whats on one input (as opposed to three). When I up to ZM_CAPTURES_PER_FRAME=3, the FPS drops significantly down to 1.5-2 FPS per monitor. Similar situation exists when I'm running two monitors - just fine at 10-12 FPS, however when I up the captures_per_frame setting to 1, the FPS drops down to 5. When I up the captures_per_frame setting to 2, the FPS drops to 2.5 per monitor. My question is why is this happening and is there a way to fix this?

(no - nothing in any of the zm/sys/messages logs).

Thank you!

Regards,

Ilya

The CAPTURES_PER_FRAME flag is intended for circumstances where you are getting interlacing problems after an input switch and want to do additional image grabs per captured frame to reduce the combing effect. As a result FPS will drop by at least a factor of whatever you set as thsi many grabs will be done for each image sent to the application. By the way, this flag should be set no lower than 1.

Unless you are trying to counteract interlacing you should not need to change this value and should be able to see images from all of your cameras provided you have set up the devices and channels correctly. If you can't that points to another problem.

Hmm - I'm not running into interlacing problems or any image quality problems. The card I have shares four inputs on one bt878 chip. When I run with CAPTURE_PER_FRAME flag set to 0 and try it with two inputs, I get one input dominating both monitors and the second input flickering every once in a while on both monitors. Both monitors at this point run at 13fps. This is why I up the CAPTURE_PER_FRAME flag. When the flag is set to 1, the fps drops to 5.0-6.0 fps. Is this happening because the capture per frame flag is forcing the chip to read an extra time and essentially dropping the fps rate? Is there anything I can do to increase my fps?

if you need more than that you need multichip cards ie a chipn per input. If you share inputs on one chip you will only see max 3 fps per input accros 4 inputs

zoneminder wrote: By the way, this flag should be set no lower than 1.

You must capture at least one frame from each camera. Otherwise it sits on one input. The single BT878 can only do a max of 30 FPS (NTSC) or 25(PAL) divided by 4 cameras is 7.5 or 6.25 (pal) frames per camera. The chip must also sync every time it changes input so you have an extra penalty for the switching. So the ideal value of of just dividing the total fps by the inputs don't work out because of the switch time and the sync time.
Also the performance can vary a bit depending on how the card is laid out (some models do a bit better than others).

Regards,
Corey

Got it - thanks guys!