Digital Video Recording
A digital video recorder (DVR), sometimes referred to by the merchandising term personal video recorder (PVR), is an electronics device or application software that records video in a digital format to a disk drive, USB flash drive, SD memory card, SSD or other local or networked mass storage device.
DVRs can usually record and play H.264, MPEG-4 Part 2, MPEG-2 .mpg, MPEG-2 .TS, VOB and ISO images video, with MP3 and AC3 audio tracks. They can also display images (JPEG and PNG) and play music files (MP3 and Ogg).
Some devices can be updated to play and record in new formats.
Recordings from standard-definition television usually have 480p/i/576p/i while HDTV is usually in 720p/1080i.
DVRs usually record in proprietary file systems for copy protection, although some can use FAT file systems.
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.
Security DVRs may be categorized as being either PC-based or embedded. A PC-based DVRís architecture is a classical personal computer with video capture cards designed to capture video images. An embedded type DVR is specifically designed as a digital video recorder with its operating system and application software contained in firmware or read-only memory.
Hardware features of security DVRs vary between manufacturers and may include but are not necessarily limited to:
- Designed for rack mounting or desktop configurations.
- Single or multiple video inputs with connector types consistent with the analogue or digital video provided such as coaxial cable, twisted pair or optical fiber cable. The most common number of inputs are 1, 2, 4, 8, 16 and 32. Systems may be configured with a very large number of inputs by networking or bussing individual DVRs together.
- Looping video outputs for each input which duplicates the corresponding input video signal and connector type. These output signals are used by other video equipment such as matrix switchers, multiplexers, and video monitors.
- Controlled outputs to external video display monitors.
- Front panel switches and indicators that allow the various features of the machine to be controlled.
- Network connections consistent with the network type and utilized to control features of the recorder and to send and/or receive video signals.
- Connections to external control devices such as keyboards.
- A connection to external pan-tilt-zoom drives that position cameras.
- Internal CD, DVD, VCR devices typically for archiving video.
- Connections to external storage media.
- Alarm event inputs from external security detection devices, usually one per video input.
- Alarm event outputs from internal detection features such as motion detection or loss of video.
Software features vary between manufacturers and may include but are not necessarily limited to:
- User selectable image capture rates either on an all input basis or input by input basis. The capture rate feature may be programmed to automatically adjust the capture rate on the occurrence of an external alarm or an internal event
- Selectable image resolution either on an all input basis or input by input basis. The image resolution feature may be programmed to automatically adjust the image resolution on the occurrence of an external alarm or an internal e vent.
- Compression methods determine quality of playback. H.264 hardware compression offers fast transfer rates over the Internet with high quality video.
- Motion detection: Provided on an input by input basis, this feature detects motion in the total image or a user definable portion of the image and usually provides sensitivity settings. Detection causes an internal event that may be output to external equipment and/or be used to trigger changes in other internal features.
- Lack of motion detection. Provided on an input by input basis, this feature detects the movement of an object into the field of view and remaining still for a user definable time. Detection causes an internal event that may be output to external equipment and/or used to trigger changes in other internal features.
- Direction of motion detection. Provided on an input by input basis, this feature detects the direction of motion in the image that has been determined by the user as an unacceptable occurrence. Detection causes an internal event that may be output to external equipment and/or be used to trigger changes in other internal features.
- Routing of input video to video monitors based on user inputs or automatically on alarms or events.
- Input, time and date stamping.
- Alarm and event logging on appropriate video inputs.
- Alarm and event search.
- One or more sound recording channels.
- Remote viewing.
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