Hello I already answered a question similar to this one so I will just post my previous answer.
for a DVR guide Wikipedia is actually quite good and if you google CCTV guide you will find tons of information.
Not all DVRs are created equal, in fact there are many options that offer varying performance much like the automobile industry. In the world of DVRs you can find the equivalent of a $10,000 Kia and a $350,000 Ferrari and everything in between. Both have 4 wheels and windshield but that where the similarities end, it’s under the hood that counts. Just like any other consumer electronic in the end you get what you pay for.
I suggest you buy a PC based DVR has they have more processing power and normally have a much smaller file size and offer more features then Standalone DVR's. I know many people buy a cheap standalone DVR, only to upgrade to a PC based in 6 months especially when they are using it to manage a store remotely. Also PC based allows you to record up to 64 cameras where a standalone will have a limit of 16.
Many people have the misconception that a PC-Based DVR is simply an off-the-shelf PC with video capture (encoder) cards, display (decoder) cards and some generic OEM software. A true DVR requires years of research and development to facilitate the seamless integration of both the hardware and software. DVRs are highly complex systems that must run 24/7, processing millions of images per day. This makes consumer-level hardware inadequate for DVRs which is why Ascendent uses custom-built PCs with performance-level hardware.
My personal favorite DVR is Ascendent X4 series: Ascendent’s Tri-Fusion Hybrid Platform allows for the creation of a true hybrid surveillance system by utilizing the advantages of Analog, Megapixel, and IP technologies for unparalleled customization and expandability. I am working on government projects and use Ascendent cameras and DVR because the offer superior performance and cost less then comparable brands like bosh, Honeywell and pelco.
The X4 also uses the latest H.264/SVC codec offer video substantially better quality,. While its file size sizes is 30% smaller than MPEG-4, 60% smaller than MPEG-2, and exponentially smaller than MJPEG.
File size is crucial to streaming because most DVR’s on the market record at real time performance (30FPS per channel) so on a 4CH is trying to send 120, 8CH 240, and a 16CH 480 images per second which requires way too much bandwidth even for the most extreme internet connections.
The smaller the files size the more images are able to be sent, and the faster they can be processed improving both FPS and speed. File size is the heart of any DVR and goes far beyond just its streaming capabilities, as it also determines the recording storage time, how much you can back up at once, how fast it renders and searches video. The file size of a DVR impacts the performance of the DVR in just about every aspect from speed to longevity and is often the most important spec of any DVR.
If you are buying a DVR and streaming is a high priority I suggest you ask for a demo and connect to the DVR to make sure it is able to stream fast enough for your needs. Most DVRs say they have remote viewing but it is often too slow and laggy to be of any use especially if it is a standalone. Some good DVR brands that I recommend are Bosch, Pelco, Honeywell and Ascendent. These brands are what security professionals use, Q-see, Swan and Lorex are only used in residential applications because they are sold by Tiger Direct, Newegg, Sams Club, Costco and other retail outlets but are not used by any security professionals also their tech support rarely speaks English as their first language...
These brand manufacturers also have a complete line of CCTV cameras for any application from residential to military.
http://www.ascendentgroup.com (Recommend)
http://www.honeywell.com
http://www.pelco.com/
http://www.bosch.com
I have done projects that required cameras to stream over satellite and cellular networks and the only DVR that could provide the video streaming was Ascendent Technology Group’s X3 DVR. To give you an example of what a good DVR should stream like, below are instructions on how to connect to Ascendent's X3 DVR using Internet Explorer.
Instructions on how to connect to Ascendent’s DVR with Internet Explorer:
1) http://connect.ascendentgroup.com/ (Must be Internet explorer)
2) Install active X control
3) Hit “Connect)
4) DVR type PC
5) DVR code SITE-100
6) User ID Demo (case sensitive)
7) Password demo (lower case)
8) Hit extend config
9) IP address: 24.66.224.223
10) And hit connect
Again I recommend going with a PC based DVR but if you don't want to spend the money I suggest Ascendent's AVP-4120 DVR or Pelco's DX-4000 as they will allow you to view all your cameras instantly from anywhere in the world using either IE. The AVP-4120 will also allow MAC platforms as well as PC to remotely view camera