Video - A Practical Guide to Video and Audio Compression - page 112

an RGB signal directly, nor will a telecine machine deliver an output in an uncompressed
form. While it is possible to design and engineer an RGB transfer system, it would be non-
standard. Only large movie-effects companies would deploy the engineering effort to
develop special-purpose hardware to do this sort of thing.
The rest of us will at best get a DV50 bit stream but more likely a DV25 bit stream in
the studio. Downstream in the consumer or semi-professional world, it is more likely that
a component signal in S-video format will be delivered. Otherwise, the best to expect is a
PAL or NTSC signal off air. While the off-air quality is reasonably good when viewed
directly, it has already been through several compression processes and converted back
and forth between analog and digital several times. The analog output from a receiver is
somewhat compromised compared to the original studio quality. The source material
could be delivered on a VHS tape running in long-play mode that is only just viewable.
These reductions in the quality all contribute to making the compression process more dif-
ficult. Many of the practicalities covered in Chapters 31 to 37 describe the remedial work
before the actual compression process begins.

5.12.2 Broadcast-Standard Digital Video

If you are working in the broadcast industry, you encounter uncompressed material and
serial digital sources that have some compression with invisible artifacts. The equipment
manufacturers refer to formats such as DV50 or DV25. Video servers used for broadcast-
ing allow these storage densities to be switched. The server will then trade off storage
capacity against production quality. It is inadvisable to change this setting while the server
is in use, as it will sometimes result in the server completely purging the video storage and
reformatting the disk array. Note also that DV25 is sometimes loosely referred to as
DVCAM.

5.12.3 Pro-Consumer Digital Video

At the top end of the consumer-grade equipment, in an area that is also populated by pro-
fessional small filmmakers or semi-professional videographers, you will find formats such
as DV. DV is slightly lossy compared with uncompressed video but the quality is a lot bet-
ter than VHS. It is compressed at a ratio of 5:1 when compared with the raw, uncom-
pressed footage. It is good enough for news gathering in many cases and the DVCAM
format is widely used. DV is output by digital home video cameras (handycams) such as
the Sony DCR PC 105.
These cameras readily connect to your Mac OS computer using the FireWire (a.k.a.
IEEE 1394 or iLink) cable and are controllable using iMovie, Final Cut Express, or Final
Cut Pro. Other video-editing tools such as Adobe Premier are equally useful. Provided
your Intel platform supports FireWire and you have the necessary applications installed,
it all works similarly on a PC.
Although you often see DV and FireWire being used together, they are distinctly sep-
arate technologies. DV is a video-storage and transfer format and FireWire is a connectiv-
ity standard. Protocols that work on the FireWire interface have been developed for the