Digital video recorders record and store video camera output in digital format on disk. These recorders can typically record from several video cameras simultaneously and can have features such as event or alarm triggering, searching ability, and adjustable frame capture rate. Digital video recorders can be in either monochrome or color format. Monochrome, or grayscale, images are presented in black, white, and grayscale. Color format presents the image in color. The range of colors is generated with varying combinations of different discrete colors. One common technique is sensing the red, green, and blue components (RGB) and combining them to create a wide spectrum of colors.

Specifications

Important performance specifications to consider when searching for digital video recorders include:

• number of video inputs
• maximum image capture rate
• image storage capacity
• maximum real-time recording
• time lapse recording
• maximum time lapse recording

The number of video inputs is the maximum number of input video channels. Most typically, they would be cameras or other signal sources; inputs may include items like video players, computers, VCRs, etc. The maximum image capture rate is the frames that can be captured per unit time, typically frames per second. The image storage capacity is the capacity of digital video storage on a hard disk or other medium. Some recorders can be programmed to record frames at specified time intervals; this feature can increase recording time. The time recording refers to the length of time that can be recorded.

Standards

Choices for video format for digital video recorders include NTSC, PAL, SECAM, RS170, RS330, and CCIR. The National Television System Committee 525-line color-television standard is used in North America and Japan. Phase Alternate Line is the European 625-line, 25-frame per second color-television standard. Sequential Color and Memory (SECAM), translated from the French Sequential Couleur Aver Memoire, is a composite color transmission system in which two color difference signals are transmitted on two separate lines. RS170 is the standard black and white video format used in the United States (525 lines, 30 frames per second). A standard recommended by EIA for signals generated by closed-circuit TV cameras scanned at 525 lines, 60 frames per second and interlaced 2:1. CCIR (Comité Consultatif International des Radio Communications, or International Radio Consultative Committee) is an international committee that sets and governs video signal standards. Color signals can be RGB, Y P_bP_r , Y/C (S-Video), and composite. 

Features

Common choices for ports or interfaces include:

• RS232
• RS422
• RS485
• parallel
• Ethernet
• modem
• SCSI
• fiber channel
• TTL
• USB 

Digital video recorders can have 8, 10, 12, 14, or 16 bits or pixels. The recording media and drive choices include hard drives, integral floppy drives, disk recording, analog tapes, and digital tapes. Common features for digital video recorders include event or motion detection, zoom capability, video searching, audio capability, multiplexing capability, and data compression. Important environmental parameters to consider when specifying digital video recorders include operating temperature, vibration rating, and shock rating.

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