Choosing your DVR

The DVR is the heart of your security system; it will ultimately control the quality of your recorded images. Its no good having very high spec CCTV cameras that are giving great live pictures on your monitor, if when you come to playback the recorded footage the recordings are totally inferior to the live image and are of no use to anybody.

There are several main things to look out for in choosing your DVR

1)     What type of compression does the DVR use.

The early DVR`s used variations of Mpeg, Jpeg,  MJpeg, or Mpeg2 etc. There are still a lot of DVRs on the market that use this compression technique. Why you may ask are they still building machines using effectively old technology. The answer is simple Recorded Image Quality. If this is the case then you may ask is why are other types of compression being used. The reason is file size, a good quality single frame image using the above compressions will use 20 – 25kbs of hard drive storage, approximately 8 times more than the very best H264 compression techniques. So if I want 30 days recording I need to use massive hard drives or reduce my frame rate to a snails pace.

Advantages.

Good recorded image quality.

Tried and tested reliable technology.

Price they tended to be cheaper.

Disadvantages

Recording times generally only good for storing one weeks recording

Frame rate generally only achieve about 6 recorded frames per camera per second.

Recommended uses.

Small CCTV system using say up to 4 cameras, not good for 8 or 16 camera systems (Use to much hard drive capacity) Great for domestic security systems or small commercial low security risk environments.

Some DVRs use Mpeg4 compression which is again well established and was the great leap forward over the old Mpeg, Jpeg etc. However not many manufacturers invested in this technology for CCTV DVRs most stayed with the older mpeg and tried to tweak it or went straight into trying to make H264 compression based DVR`s.

My personnel opinion is this was a mistake because I believe that Mpeg4 gives the best compromise for CCTV image recording in the terms of Image quality, frame rate, storage capacity, price and reliability.

A good quality Mpeg4 DVR will use about 4 - 6kbs of storage space per frame at 704 x 576 pixels or D1 resolution as it is commonly referred to. This means that 30 days recording is achievable using modern high capacity hard drives i.e. a 500gb hard drive will record 4 cameras at D1 resolution at 8 frames per second for more than 30 days.

Very few Mpeg4 based DVRs will record at real time frame rates say 15 – 25 frames per second per camera without reducing image size and quality. However most will do between 7 – 10 fps at D1  resolution. This frame rate is acceptable for most security system applications and exceeds most police forces requirements.

The recorded images are of a quality very similar to the live image and do not suffer from the blocking effect associated with H264 compression. Also the image size is small enough to make transmission of live pictures over networks or the internet of a reasonable quality and speed.

Advantages

Good recorded image quality

Good frame rate at high image quality

Tried and tested technology

Value for money.

Disadvantages

Not capable of true real time recording.

Mainly available as PC based DVRs rather than standalone

Recommended uses.

Great for any installation that needs to meet police  requirements. Good for 4 8 and 16 camera systems.