Why Video Compression Is Needed - A Practical Guide to Video and Audio Compression - page 32

2.9.6 Personal Video Recorders

Personal video recorders ( PVR s) are often generically referred to as TiVo , although they are
manufactured by a variety of different companies. Some of them do indeed license the
TiVo software, but others do not. Another popular brand is DirecTV.

2.9.7 Analog Off-Air PVR Devices

A classic TiVo device works very hard to compress incoming analog video to store
it effectively and provide trick-play features. The compression quality level can be set
in the preferences. The compromise is space versus visible artifacts. At the lowest qual-
ity, the video is fairly noisy if the picture contains a lot of movement. This is okay if you
are just recording a program that you don't want to keep forever—for example, just
a time shift to view the program at a different time. If you want to record a movie,
you will probably choose a higher-quality recording format than you would for a news
program.
The functionality is broadly divided into trick-play capabilities and a mechanism to
ensure that you record all the programs you want to, even if you do not know when they
were going to be aired.
In the longer term, these devices scale from a single-box solution up to a home media
server with several connected clients. This would be attractive to schools for streaming TV
services directly to the classroom. University campus TV, hospital TV services, and corpo-
rate video-distribution services are candidates. Standards-based solutions offer good
economies of scale, low thresholds of lock-in to one supplier, and good commercial oppor-
tunities for independent content developers.

2.9.8 Digital Off-Air PVR Devices

When digital PVR devices are deployed, recording television programs off-air becomes far
more efficient. In the digital domain, the incoming transport stream must be de-multi-
plexed, and packets belonging to the program stream we are interested in are stored on a
hard disk. The broadcaster already optimally compresses these streams. Some storage ben-
efits could be gained by transcoding them. Note that we certainly cannot add any data
back to the video that has already been removed at source.
Future development work on PVR devices will focus on storing and managing con-
tent that has been delivered digitally. This is within the reach of software-based product
designs and does not require massive amounts of expensive hardware.
There are complex rights issues attached to home digital-recording technology, and
it is in constant evolution.

TiVo: http://www.tivo.com/
DirecTV: http://www.directv.com/