The Pre-alarm record mode is the record mode for recording a pre-alarm event for a specified time period before recording an alarm event. 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.

Video isn't recorded in the Pre-alarm record mode for cameras without video compression that are added to the corresponding list in the Video subsystem section of 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:

  1. Go to the Hardware tab in the System settings window.
  2. Select the Camera object corresponding to the adjusted camera in the object tree.
  3. Select the Basic settings tab on the settings panel of the Camera object.
  4. In the Pre-alarm record field, specify the time interval in seconds during which the pre-alarm event is recorded.
  5. 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, you can perform recording in the Pre-alarm record mode if the camera is disarmed. You can do it using the DoReact("CAM","1","REC","rollback<1>") program (see The Script object. Programming using the JScript language).

If you specify a long pre-record time, it can result in increasing the waste of running memory. The recommended pre-record time is no more than 20 seconds.

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 in length to the archive (maximum size, by default) and use the following formula:

Note that the frame size also depends on the percent of motion in the frame.

You can count the size of the pre-record buffer for one camera if the frame size is known:

General memory consumption in the Pre-alarm record mode is determined by the sum of values received for each camera.

If cameras perform pre-recording with equal frame frequency, you can use the following formula:

Example.

The camera performs pre-recording for 15 seconds with a hot record speed of 25 fps. The size of the 500-frame fragment is 20 MB. You must determine the size of the pre-record buffer for such a camera.

First, you must determine the average frame size:

  • Frame size = Fragment size / 500 = 20 MB / 500 frames = 0.04 MB.

So, the size of the pre-record buffer is:

  • The memory consumption in the Pre-alarm record mode for one camera, MB = Pre-alarm record time, sec * Frame rate in the Pre-alarm 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.