Personal video recorder

From open-encyclopedia.com - the free encyclopedia.

The personal video recorder (PVR), also called digital video recorder (DVR), is a consumer electronics device that records television shows to a hard disk in digital format.

This makes the "time shifting" feature (traditionally done by a VCR) much more convenient, and also allows for "trick modes" such as pausing live TV, instant replay of interesting scenes, and skipping advertising. Most PVR recorders use the MPEG format for encoding analog video signals.

The most popular PVRs on the market are TiVo's TiVo and DNNA's ReplayTV. Many satellite and cable companies are incorporating PVR functions into their set-top box, such as with DirecTiVo, or Sky+. In this case there is no encoding necessary in the PVR, as the satellite signal is already a digitally encoded MPEG stream. The PVR simply stores the digital stream directly to disk. Having the broadcaster involved with (subsidizing) the design of the PVR, and directly recording encrypted digital streams can lead to fancy features - like the ability to use interactive TV on recorded shows, pre-loading of programmes; but can also lead to too much control by the broadcaster - like denying the ability to skip adverts and automatically expiring recordings after a time determined by the broadcaster.

Upcoming entrants into the market include products such as Digeo's Moxi, and Microsoft's Media Center.

In 2003, the Yakima, Washington Police Department began using PVRs in their patrol cars to record the activities of officers and suspects. Since then, many other police departments have followed suit, due to the increased reliability and decreased cost compared to analog video systems.

There are ways to make one's own PVR using software and hardware available for Microsoft Windows, Linux and Macintosh operating systems. There are even people working on turning the Xbox into a PVR with a modchip.

How a digital/personal video recorder works

Analog

Analog TV in NTSC, PAL or SECAM formats, analog cable, or regular VHS tapes use a signal that is fed directly to the electron beam within the television set. There are a number of details on how this is done, but in essence each pixel in each frame corresponds to a specific fraction of time within the signal.

To record an analog signal two steps are required. First, a TV tuner card that digitizes the signal. The signal must be digitized since a computer hard drive records things in a digital file format. Second, the video stream/signal must be compressed into a manageable format, like MPEG-2 otherwise the hard-drive would quickly fill up. Some TV tuner cards like the PVR-250 are able to perform both steps.

Broadcast Digital

Broadcast digital are digital television signals that are broadcast over the air. This is the same as how analog is broadcast over the air, however it is in a digital format. Recording broadcast digital signals is, in its simplest form, a straightforward capture of the binary MPEG-2 data being received; no further hardware is required to digitise the signal or compress it (as the televsion broadcaster has already done this). An added layer of complexity, found in many modern PVRs, is the re-compression of the audio/video data after reception (either "on-the-fly" or as a post-process) in order to make best use of available storage space.

Satelite or Digital Cable

Recording satellite or digital cable signals on a personal video recorder is more complex than recording analog signals or broadcast digital singals. This is so because the MPEG-2 stream is usually encrypted to prevent people from viewing the content without paying for it (usually via subscription to a valid satelite decryption box and a decoder card).

The satelite or cable decoder box does two things. First it decrypts the signal. Second, it decodes the MPEG-2 stream into an analog signal for play on the television. In order to record cable/satelite digital signals you would need to get the signal after it is decrypted but before it is decoded (between steps one and two).

An alternative is that some satellite/cable decoder boxes have a firewire port that can be connected to a computer. The MPEG stream could be relayed to the computer via this firewire port although there is as yet few, if any, current cards or devices that allow for a firewire connection to the computer from this box.

PVR software

There is PVR software available for Linux and Windows for people who make their own homemade recorders.

Linux

The two main PVR applications for Linux are MythTV and Freevo both of which are GPL open source software.

Macintosh

El Gato makes a PVR device called EyeTV.

Windows

Microsoft Windows has several open source PVR applications including GB-PVR, OpenHTPC, and Media Center Portal

There also are several proprietary applications including SageTV, BeyondTV, ChrisTV , Showshifter and Recordit Plus

See also: Hard disk recorder, DVD recorder

External links

• PVR Guide - How to guides for installing PVR software
• Video Disk Recorder - Open source Linux PVR software for Digital television
• Dreambox - PVR for Digital television
• Nokia Mediamaster 260T - PVR for terrestrial Digital television
• Freevo - Open-source Linux PVR
• MythTV - Yet Another Linux PVR
• InteractTV Telly - A Linux-based PVR appliance with a loyal developer following
• PVR Resource - great resource on open source PVR's
• Recordit Plus - PVR software for windows
• GBPVR - Another free media center style application for windows

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