How DVR Works

In a nutshell, a DVR is a glorified hard drive inside a fancy box that looks nice in your entertainment center. The hard drive is connected to the outside world through a variety of jacks on the back of the box, usually the typical RCA connections that you would use to hook up, say, a cable box or a VCR.

­The television signal comes into the DVR's built-in tuner through antenna, cable or satellite. If the signal comes from antenna or cable, it goes into an MPEG-2 encoder, which converts the data from analog to digital (MPEG-2, by the way, is the compression standard used to fit information onto a DVD). From the encoder, the signal is shipped off to two different places: first, to the hard drive for storage, and second, to an MPEG-2 decoder, which converts the signal back to analog and sends it to the television for viewing.

Some systems use dual tuners, allowing users to record different programs on different channels at the same time. On a few systems, you can even record two programs while watching a third pre-recorded show.

The device is driven by a customized operating system -- for instance, in the case of TiVo, the machine runs on a highly modified Linux installation. The operating system resides on the hard disk, along with the recording space, a buffer for live broadcasts, and in some cases a space for future expansion.

While the system might seem pretty ho-hum on first analysis, the digital storage of television signals opens up a whole new world of possibilities when it comes to playback and viewing.

­First, a DVR is tapeless. With a VCR, the device itself is merely a recording tool; the blank cassette is the media. In a DVR, the media and tool are one and the same. This is obviously a plus if you never seem to be able to find a blank tape when it's time to record something, but it can also be a drawback. Because the media is hard-wired into the machine, adding additional storage space is not possible. There are Web sites that offer instructions on how to open a DVR and add a new hard drive, but beware -- this will definitely void your warranty. Getting more recording time is easy with a VCR -- just buy another box of blank tapes. More recording time on a DVR involves buying a new unit.

You can incorporate some DVRs into your home network, which can allow you to access your system remotely. You could set your DVR to record a specific show from halfway across the world with just a few clicks of your mouse.

Perhaps the most important benefit of DVRs is the unprecedented control over playback. With a VCR, you have to wait for a program to finish recording before you can start watching it. Since there's no tape to rewind, digital recording doesn't have this limitation. A program that started recording 10 minutes ago can be viewed at any time, even while it's still recording.

Pausing Live TV

One of the main features of a DVR, and one that is hyped heavily in product advertisements, is the ability to "pause live television." This feature has caused more than a few people to scratch their heads, wondering exactly how this is done.

The phrase "pause live TV" is a bit misleading. DVRs are constantly recording to a live TV buffer. When you hit the pause button on a DVR remote, it freeze-frames the current image, giving the appearance of a paused videotape. When you hit play (un-pause), the recorded program begins playing.

DVRs generally keep the past hour or so in the buffer. This means that if you walk into the room 10 minutes into a movie, you can rewind it and catch the beginning -- provided the DVR was on the desired channel (the buffer is emptied each time you change the channel, and the DVR starts recording again).

Search Tools

Some of the most desirable features of DVRs are the tools they offer to help you find the programs you want to record.

All DVRs offer search tools of some sort, usually by name of program, name of actors, and in some cases more sophisticated options such as keyword searches.

The TiVo service offers two functions aimed at people who know what they want to watch: Wish Lists and Season Passes. Wish Lists allow you to type in (using an on-screen keypad) names or keywords that you want to keep an eye out for. For instance, a Wish List might look for everything starring Frank Sinatra, or any animated program with the word "dragon" in the title.

Season Passes allow you to tell the machine to record every instance of a single program, with the option of some advanced specifications. For instance, you can simply tell it to always record "Law and Order," or you can tell it to only record first-run episodes.

DVRs advertise anywhere from 35-hour to over 300-hour recording capabilities. It's worth noting that these units can record programs at varying levels of quality -- and the advertised capacity usually refers to the number of hours it can hold at the lowest quality setting.

­As an example, TiVo can record programs at four different quality levels: basic, medium, high, or best. A 40-hour TiVo unit can hold 40 hours at the basic quality level, but only about 11 hours at the best setting. The hard drive in a 40-hour TiVo is approximately 40 gigabytes in size; on the basic setting, one hour translates to 1 gigabyte, while at the highest setting one hour uses 4 gigabytes.

Newer DVR systems can record HDTV signals. The Series3 HD TiVo can record up to 300 hours of standard television (on the Basic quality setting) or up to 32 hours in HD format.

So what's the difference? If you've ever seen full-motion video on the Web, you know how images can get blocky and distorted. This happens on DVR recordings made at low quality levels, particularly if there is a lot of movement in the image. As a result, different quality settings are good for different types of programs: while an old black-and-white movie or a talk show will look just fine at the basic level, a fast-moving sports program or action movie will be almost unwatchable. So bear this in mind if you're thinking of buying a DVR primarily to support your sports habit -- better to go for the higher capacity unit.

File Sizes

In Sony's Giga Pocket system, the files for each recorded program are stored on the computer's normal hard disk. If you have a drive with 60 free gigabytes of space, then Giga Pocket can use those 60 gigabytes to store TV programs. The amount of space that a program consumes on the hard disk depends on both the length of the program and the recording quality. Giga Pocket offers three quality modes:

In other words, you can store about 100 hours of video on 60 gigabytes of space in LP mode. In SP mode, you can store about 36 hours. In HQ mode, you can store about 18 hours.

In terms of quality, LP mode has a noticeable grain to it, but it's watchable. SP mode looks good. HQ mode seems like overkill -- there's not a noticeable difference between SP and HQ when you are watching a program recorded from cable. Perhaps if you were recording an s-video signal coming in from a DVD player or camcorder and you wanted to preserve all the detail, HQ mode would be useful.

Just like on a computer hard drive, deleting a program from a DVR doesn't actually delete the program itself -- it simply erases the file system's reference to where it's stored and how long it is, making it effectively gone. The raw program data remains on the drive until it is overwritten by a new recording.

Unlike a VCR, DVRs usually have a monthly fee associated with their use. This is because the devices dial into a server once every few days and download new program grids (some DVRs need access to a telephone line, but can be configured to dial in the middle of the night, or at other times when the line is likely to be clear; other DVRs can access program grids through a broadband connection in your home network).

TiVo charges a set monthly fee, though it once offered the option of paying a larger amount once for a "lifetime subscription" (lifetime of the unit, that is). Cable companies that offer DVR packages are usually more expensive than standard cable packages. Some manufacturers offer DVRs that aren't linked to a particular service and don't require ongoing fees at all.

If you don't mind watching your shows on the small screen, an alternate solution exists for PC owners: products like the ATI All-In-Wonder and Sony Giga Pocket cards allow you to capture television signals digitally to your computer's hard drive, in essence using your PC as an elaborate DVR. There is no monthly fee to pay, but you also miss out on some of the advanced features such as constantly updated program grids, Season Passes and the like. Giga Pocket allows you to save recorded programs to VHS or DVD-R, and most video-capture boards have "video out" jacks, making it possible to wire your television to the computer.

ReplayTV, once a direct competitor with TiVo in the standalone DVR box market, now produces DVR software and hardware for PCs. Users must purchase a separate tuner card for their machine. The ReplayTV software provides many of the features found in competing DVR systems.

For lots more information on DVRs, recording devices and related topics, check out the links on the next page.

A digital video recorder (DVR) enables you to record programs from your television. DVRs are versatile and make it more user-friendly to record and play back TV programs [source: Britannica]. DVRs allow you to watch one show while recording another one at the same time or to record two shows while watching a show that you recorded previously [source: Dishnetwork].

You will have to connect your DVR to your TV before you can use it, which will require a separate radio frequency (RF) modulator. Before starting the process, unplug any electronic devices involved in the installation and choose a place for the DVR. Make sure the cables are long enough to reach the TV from that location.

You're now ready to connect your DVR to a TV. Here's how to connect your DVR to a standard TV.