05-10-2012, 05:30 PM
Digital video recorders
Digital video.doc (Size: 230 KB / Downloads: 26)
Introduction
Digital Video Recorders (DVRs) are TV set-top boxes allowing people to record at least 15 to 200 hours of video. As
personalized agents, these devices help users choose and organize the programs that they like to watch at the times they want
to watch them. With DVRs, viewers can pause, rewind, and fast forward programs during recording. Advanced DVRs allow
users to automatically skip commercials by offering 30-second jumps (ad-skipping). Finally, some DVRs provide the option
to redistribute copied programs or video content among friends.
With these features, DVRs may fundamentally change the business models, in particular, the models of programming choice
of TV stations and cable / satellite service providers.
The overriding decision for a TV station, aiming a financial success, is which programs to deliver to the end-consumer. Cable
operators or digital satellite broadcasters need to decide which networks to carry, which content to show, and how to bundle
their offerings to optimize profitability. These decisions, derived from programming choice questions, make up a good part of
their so-called business model.
Of course, the extensive literature on business models (among many others, Afuah and Tucci 2001; Amitt and Zott 2001;
Magretta 2002; Turban, E., King, D., Warkentin, M. and Chung, M. 2002) and on business model taxanomies (e.g., Timmers
1999; Rappa 2000; Tapscott, D., Ticoll, D. and Lowy, A. 2000) also covers many additional aspects in-depth.
Purpose
Digital video recorders configured for physical security applications record video signals from closed-circuit television cameras for detection and documentation purposes. Many are designed to record audio as well. DVRs have evolved into devices that are feature rich and provide services that exceed the simple recording of video images that was previously done through VCRs. A DVR CCTV system provides a multitude of advanced functions over VCR technology including video searches by event, time, date and camera. There is also much more control over quality and frame rate allowing disk space usage to be optimized and the DVR can also be set to overwrite the oldest security footage should the disk become full. In some DVR security systems remote access to security footage using a PC can also be achieved by connecting the DVR to a LAN network or the Internet. Some of the latest professional digital video recorders include video analytics firmware, to enable functionality such as 'virtual tripwire' or even the detection of abandoned objects on the scene.
Definitions, Acronyms, Abbreviations
Definition of: DVR
(1) (Digital Video Recorder) A security system device that records the video from up to 16 surveillance cameras on a hard disk. The frame rate can be switched from real time to time lapse in order to save disk space. Digital recorders are more flexible than earlier analog VHS tape systems, and the video can be easily transmitted over a computer network.
(2) (Digital Video Recorder) Also known as a "personal video recorder" (PVR) or "hard disk recorder," a DVR is a consumer device that allows the viewer to pause and rewind any broadcast, cable or satellite TV program as well as record and play back selected programs (see live pause). An order of magnitude more flexible than VCRs, an entire season of programs from one or more favorite series can be recorded.
Hardware Interfaces
Security video applications are moving to higher recording and display resolutions. CIF resolution recording (NTSC 360 x 240) was used extensively in early generation DVRs to produce digital video quality comparable to the analog VCR it replaced. Low-resolution CIF was also well suited to first-generation codec technology (MJPEG/MPEG-4) that cannot produce acceptable compression ratios at higher resolutions. The market requirement today and moving forward is standard-definition (D1 NTSC 720 x 480) or "DVD-quality" video recording. Standard definition (SD) represents a fourfold performance increase in system processing power per channel as compared to CIF. State-of-the-art H.264 codec technology is used at D1 resolution and above to ensure efficient compression ratios. Maxim's family of H.264 processors allows programmable video resolutions for recording at any level of quality required.
Another trend in security and surveillance video is the requirement for full-frame-rate video recording and storage. Full frame rate for an analog CCTV camera is 30 frames per second (fps) in NTSC and 25fps in PAL. Real-time video recording represents a twofold to fourfold increase in processing power required per channel versus DVR designs that record at reduced frame rates such as 7.5fps (25% in NTSC) or 15fps (50% in NTSC). A powerful, scalable system architecture is required to meet the processing requirements of new DVR designs.