As illustrated above, the analog signal from the camera is sent to
the DVR. From there, it is sent to the PC or TV/OUT monitor for viewing, and
compressed in MPEG-4 format.
MPEG-4 is a great way to reduce memory usage because it stores
only the changes from one frame to another. Take for instance, a stationary
camera pointed at a room. Everything remains the same except for the person
moving in the room. What MPEG-4 does, is it records the background once in
the beginning and tracks and records the changes, or the person in the room,
reducing the amount of data. This compression allows the DVR to transmit
surveillance images through the internet because it uses less bandwidth.
Another way to compress video is with Motion JPEG, or MJPEG. Unlike MPEG-
4, it stores the whole frame in JPEG format in sequence. MJPEG produces
clearer picture, but uses significantly larger amount of data, and makes
remote viewing difficult due to high bandwidth requirements.
The compressed data is recorded onto the hard drive or sent over
the Internet for remote viewing. The recorded images, now digital, can be
easily searched or copied to CD, DVD, or any other memory device hooked to
the system.
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