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Glossary: Pre/post alarm image buffer

A useful camera feature in security installations are the pre and post alarm image buffer.  When a camera alarm is triggered it can upload images or footage to a server for later use.  A pre image buffer allows the viewer to see what happened before the alarm was triggered e.g. which direction a person walked into the camera’s view from.  A post image buffer stores any images which have been captured after the alarm has been triggered.

A pre-buffer alarm is useful when you wish to capture images directly before an event.   Most IP cameras allow you to specify the length of the pre-buffer when setting up the event and these images will be recorded along with the event recording.  The buffered images can then be sent to the user.  The same is true of the post image buffer but these images are captured after a trigger event.

There are a few ways in which images can be sent from the camera.  Images can be emailed using an SMTP mail server.  This is done by adding the SMTP account settings into the camera and choosing an address to send the images to.  Another way of sending images from the camera is using the File Transfer Protocol.  FTP allows the user to transfer images to another device which has an FTP server or client running.

The size of an image buffer is often the main factor in estimating how much images and footage an image buffer can store, for example the Axis 210A can hold 9MB (up to 5 min of 320×240 video at 4 fps) buffered images or footage.

Published on July 17th, 2008 by James Drinkwater

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