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Update definemonitor.rst

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Andrew Bauer 2016-08-06 16:34:00 -05:00 committed by GitHub
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docs/userguide/definemonitor.rst
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@ -46,11 +46,20 @@ Linked Monitors
This field allows you to select other monitors on your system that act as triggers for this monitor. So if you have a camera covering one aspect of your property you can force all cameras to record while that camera detects motion or other events. You can either directly enter a comma separated list of monitor ids or click on ‘Select’ to choose a selection. Be very careful not to create circular dependencies with this feature however you will have infinitely persisting alarms which is almost certainly not what you want! To unlink monitors you can ctrl-click.
Maximum FPS
On some occasions you may have one or more cameras capable of high capture rates but find that you generally do not require this performance at all times and would prefer to lighten the load on your server. This option permits you to limit the maximum capture rate to a specified value. This may allow you to have more cameras supported on your system by reducing the CPU load or to allocate video bandwidth unevenly between cameras sharing the same video device. This value is only a rough guide and the lower the value you set the less close the actual FPS may approach it especially on shared devices where it can be difficult to synchronise two or more different capture rates precisely. This option controls the maximum FPS in the circumstance where no alarm is occurring only. (Note for IP cameras: ZoneMinder has no way to set or limit the mjpeg stream the camera passes, some cams you can set this through the url string, others do not. So if you're using mjpeg feeds you must NOT throttle here at the server end, only the cam end. If you want to use this feature, the server to throttle, then you MUST use jpeg instead of mjpeg method to get picture from the camera)
On some occasions you may have one or more cameras capable of high capture rates but find that you generally do not require this performance at all times and would prefer to lighten the load on your server. This option permits you to limit the maximum capture rate to a specified value. This may allow you to have more cameras supported on your system by reducing the CPU load or to allocate video bandwidth unevenly between cameras sharing the same video device. This value is only a rough guide and the lower the value you set the less close the actual FPS may approach it especially on shared devices where it can be difficult to synchronise two or more different capture rates precisely. This option controls the maximum FPS in the circumstance where no alarm is occurring only.
This feature is limited and will only work under the following conditions:
#. Local cameras
#. Remote (IP) cameras in snapshot or jpeg mode **only**
Using this field for video streams from IP cameras will cause undesirable results when the value is equal to or less than the frame rate from the camera. Note that placing a value higher than the camera's frame rate is allowed and can help prevent cpu spikes when communication from the camera is lost.
Alarm Maximum FPS
If you have specified a Maximum FPS it may be that you don’t want this limitation to apply when your monitor is recording motion or other event. This setting allows you to override the Maximum FPS value if this circumstance occurs. As with the Maximum FPS setting leaving this blank implies no limit so if you have set a maximum fps in the previous option then when an alarm occurs this limit would be ignored and ZoneMinder would capture as fast as possible for the duration of the alarm, returning to the limited value after the alarm has concluded. Equally you could set this to the same, or higher (or even lower) value than Maximum FPS for more precise control over the capture rate in the event of an alarm.
**IMPORTANT:** This field is subject to the same limitations as the Maxium FPS field. Ignoring these limitations will produce undesriable results.
Reference Image Blend %ge
Each analysed image in ZoneMinder is a composite of previous images and is formed by applying the current image as a certain percentage of the previous reference image. Thus, if we entered the value of 10 here, each image’s part in the reference image will diminish by a factor of 0.9 each time round. So a typical reference image will be 10% the previous image, 9% the one before that and then 8.1%, 7.2%, 6.5% and so on of the rest of the way. An image will effectively vanish around 25 images later than when it was added. This blend value is what is specified here and if higher will make slower progressing events less detectable as the reference image would change more quickly. Similarly events will be deemed to be over much sooner as the reference image adapts to the new images more quickly. In signal processing terms the higher this value the steeper the event attack and decay of the signal. It depends on your particular requirements what the appropriate value would be for you but start with 10 here and adjust it (usually down) later if necessary.