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The Pre-alarm record mode is the record mode for recording a pre-alarm event for a specified period before recording an alarm. Pre-alarm recording is performed at the hot record rate. If you don't specify the hot record rate, then the recording is performed at the standard record rate.
Attention!
Video isn't recorded in Pre-alarm record mode for cameras without video compression that have been added to the corresponding list in the Video subsystem section in the tweaki.exe utility (see The Settings panel of the Video subsystem section).
By default, the recording in this mode is disabled. To enable the pre-alarm recording, do the following:
- Go to the Hardware tab in the System settings window.
- Select the Camera object corresponding to the required camera in the objects tree.
- Go to the Basic settings tab on the settings panel of the Camera object.
- In the Pre-alarm record field, specify the time interval (sec) of pre-alarm events recording.
- Click the Apply button.
The table provides the information on pre-alarm recording options.
Camera state | Recording initiator | Recording |
Armed | Macro | Without pre-alarm recording |
Armed | Manually | Without pre-alarm recording |
Armed | Alarm | With pre-alarm recording |
Armed | Program | With pre-alarm recording |
Disarmed | Macro | Without pre-alarm recording |
Disarmed | Manually | Without pre-alarm recording |
Disarmed | Alarm | Na |
Disarmed | Program | With pre-alarm recording |
In Axxon PSIM one can perform pre-alarm recording if camera is disarmed. You can do it with the help of the DoReact("CAM","1","REC","rollback<1>") program; (see The Script object. Programming using the JScript language).
Specifying the long pre-record time can result in increasing the waste of running memory. Recommended pre-record time is not more than 20s.
To count the memory consumption, figure out the average size of the video signal frame. To do this, you must record the video fragment of 500 frames length to the archive (maximum size, by default) and use the following formula:
Frame size = Fragment size / 500
Note, that the frame size also depends on percent of motion in the frame.
You can count the size of pre-record buffer for one camera if the frame size is known:
Size of pre-record buffer for one camera, MB = Pre-record time, sec * Frame frequency in the pre-record mode, fps * Frame size, MB
General memory consumption in the pre-record mode is defined by sum of values for each camera.
If cameras perform pre-record with equal frame frequency, you can use the following formula:
Size of pre-record buffer for all cameras in the system, MB = Number of cameras * Pre-record time, sec * Frame frequency in the pre-record mode, fps * Frame size, MB
Note
Example.
The camera performs pre-record for 15 seconds with the hot record speed 25 fps. Size of 500-frames fragment is 20 Mb. It is required to define the size of pre-record buffer for such camera.
First, it is necessary to define the average frame size:
Frame size = Fragment size / 500 = 20 MB/500 frames = 0.04 MB
So, the size of pre-record buffer is:
The memory consumption in the pre-record mode for one camera, MB = Pre-record time, sec * Frame frequency in the pre-record mode, fps * Frame size, MB = 15 sec * 25 fps * 0.04 MB = 15 MB.
Configuring video in the pre-alarm record mode is complete.
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