By the mid-1990s, the video surveillance industry saw its first digital revolution with the introduction of the DVR. The DVR, with its hard drives, replaced the VCR as the recording medium. The video was digitized and then compressed to store as many days’ worth of video as possible.
With early DVRs, hard disk space was limited, so the recording duration was limited or a lower frame rate had to be used. Due to the limitations in hard disk space, many manufacturers developed proprietary compression algorithms. Although they might have worked well, end users were tied to one manufacturer's tools when it came to replaying the video. As the cost of hard disk space decreased dramatically over the years and standard compression algorithms such as MPEG-4 became available and widely accepted, most manufacturers gave up their proprietary compression in favor of standards — to the benefit of end users.
Most DVRs had several video inputs, typically 4, 16, or 32, which meant they also included the functionality of the quad or multiplexer.
DVR system provided the following major advantages:
- · No tapes and tape changes
- · Consistent recording quality
- · Ability to quickly search through recorded video
Early DVRs used analog monitors such as TV sets for showing video.
However, because the DVR made digital video available, it became possible to network and transmit the digital video over longer distances. This function was first addressed by connecting a phone modem to a serial port on the DVR. Later, the phone modem was built into the DVR itself.
Although the ability to monitor the video remotely via a PC was a great benefit, the actual functionality was not extremely useful because the bandwidth available with phone modems was too low, often in the 10- to 50-kbps range. That meant very low frame rates, low resolution, or highly compressed video, which made the video more or less useless.
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