Sky+, TiVo…What is a digital video recorder?

Sky+, TiVo, Freeview+ and Freesat+: what do they all have in common? They’re all DVRs, or digital video recorders.

This is the digital TV version of your faithful old VCR, but instead of copying analogue TV to a tape at low quality, it captures the exact digital TV data that’s transmitted to you, so it’s a perfect copy of what you see on screen.

Inside your typical DVR is a digital TV tuner and some kind of digital storage, plus the chips to decode the audio and video signals and send them to your TV, either live or from the digital storage.

The tuner can be for Freeview, digital satellite TV (Freesat or Sky), or digital cable (Virgin), and it decodes the off-air signal to extract the individual TV channels. Most DVRs have two tuners, so that you can watch one TV channel while you record another, but Virgin’s TiVo has three and we expect to see quad-tuner DVRs on sale in future. In Japan, Toshiba sells a DVR with eight tuners!

Storage

Most DVRs use a hard disc to store TV, like the one in your PC. Sky+ launched with a 40GB disc, but there’s always a ‘sweet spot’ for hard disc prices, which is currently around 500GB, with an affordable high-end of 1TB (1,000GB). The sweet spot usually increases as hard disc manufacturers get better at squeezing in more data, although when it eventually hits 1TB that will probably be enough for most people.

Some DVRs let you plug in a USB memory stick or hard disc to expand the built-in memory, or turn a simple single-tuner digital TV box (or zapper) into a DVR. If you’ve got Freeview or Freesat, you can get a DVR with both a hard disc and a Blu-ray or DVD recorder, for making copies to share or save for posterity.

A single hour of standard-definition TV usually takes about 2GB, while high definition TV only takes about 3GB an hour, because they use different digital TV formats (except on Virgin, where it’s almost 6GB a hour). That’s only a rule of thumb, however, because some TV channels broadcast at very low quality that takes up less space, while sports and action movies take up more space because they’re more detailed.

Features

Apart from being able to instantly access your recordings on the hard disc, DVRs let you pause, rewind and fast-forward and watch in slow motion (known as ‘trick play’) without losing any detail. Fast forward can be anything up to 60x normal speed, which makes it really easy to skip the ad breaks. Some DVRs, like Sky+, even let you choose where to start playing.

If you’re watching live TV, DVRs usually record to a ‘buffer’ which stores the last hour of your current channel, so you can instantly pause or rewind, then catch up as fast as you want. Known as ‘pause live TV’ or ‘chasing playback’, it’s handy if the phone rings or you want to see that goal again.

The final big benefit over an old-fashioned VCR is that a DVR should have a programme guide (electronic programme guide or EPG) that you can browse to see what’s on over the next week (or 14 days with Virgin). You can also use this to record a show with one or two clicks of a button, and even set up a ‘series link’ to record every episode (Virgin’s TiVo calls this a Season Pass).

Automatic recordings can often be customised to add extra time at the start and finish in case programmes over-run, and there’s usually a manual timer somewhere if you need it.

Typical DVR recording times

Hard disc size	320GB	500GB	1TB
Standard definition	230 hours	360 hours	740 hours
High definition	80 hours	125 hours	240 hours

Recording times assume Standard Definition at 1.4GB/hour using MPEG-2; High Definition at 4GB/hour using MPEG-4 H.264 at 1080i

What to look for: 

• How many TV tuners does it have? 
• How much storage does it have?
• Can you pause live TV (chasing playback)?
• How fast can you pause or rewind?
• How many days does the EPG cover?
• Can I set up series links?