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Video
Formats Suitable for DVD
Paulo de Andrade
There's an old saying in the industry: Garbage in, garbage out. It couldn't
be truer for DVD encoding. All DVD producers want their shinny discs to
look great. After all, one of the advantages of the medium is to offer viewers
virtually the same image quality that you and I can see in the studio. And
DVD makes this possible for the first time ever.
Gone are the quality losses that we've had to live with for so many years
when VHS and laserdisc were the only available consumer formats. But, in
order to deliver this killer quality level, a lot of attention must be paid
to the encoding (or transcoding) process. Several elements influence the
encoding process, but the most important ones are the quality of the original
material and the required media (DVD) space.
You should never expect a DVD created from a second-generation S-VHS edited
master to look as good as a commercial DVD that started with professionally
scanned 35mm film stored on uncompressed D1 or D5 digital videotape. MPEG-2
compression doesn't fix bad video. At best it replicates it. In reality,
bad video can make the compressed movie look even worse and take up a lot
more storage space. That's because S-VHS (or any other consumer/prosumer
analog format, for that matter) is very noisy. The colors are noisy because
the frequency response of these formats is much lower than that of broadcast
or digital formats. And the luminance part of the video is noisy for the
same reasons. Plus let's not forget the resolution (or lack of) issue. Put
these elements together and you end up with a recipe for sub-standard DVDs.
After all, consumers do expect DVD video to look great.
Noisy video can be particularly bad because MPEG-2 compression is lossy
as it discards redundant information in order do save storage space. It
can be a very efficient CODEC when there is very little change within a
shot or between frames. The problem with video noise is that it's completely
random and its pattern changes entirely from frame to frame. The MPEG-2
encoder doesn't know what is video information and what is noise and all
it sees are a lot of changing pixels. Therefore, it will produce much larger
files. And here is where the amount of available space plays a very important
role. If the presentation is short (up to 1 hour long), you can use a very
high bitrate and the encoder will still give you great looking video (as
good as the original, anyway). But if your presentation is longer, you must
throw away some information in order for the video to fit on a DVD. If you
use fixed bit rate encoding, you will have to compromise the quality of
the final product. And even if you use variable bitrate encoding, the noise
causes so many changes between frames that there's not much that the encoder
can do to create smaller files.
If you are creating a DVD from scratch, always use the best quality source
you can obtain. Digital video formats are great for DVD because they are
virtually noise free, have solid colors and high frequency response. Uncompressed
formats such as D1 and D5 are the best, followed by compressed formats such
as DigiBeta, D9 and DVCPro 50. Next come DVCam, DVCPro and DV, which in
spite of being more compressed can produce outstanding results if the sources
are of high quality. In fact, there's a huge difference in image quality
coming from a broadcast-quality DV camera and a prosumer model. Most of
the artifacts associated with DV are completely eliminated or become practically
invisible. On the other hand, consumer DV cameras must be avoided because
they produce video that looks very amateurish. As a minimum requirement,
a DV camera must have 3 CCDs in order to produce decent colors.
All these digital formats use component video signals, just like DVD, which
means that the encoded color signals will remain separate and the image
will look better defined with no bleeding edges or chroma crawl. Beta SP
or MII are analog formats that produce great results because of very low
noise, stable colors and good resolution. They are also component formats,
which is a big plus. Most other formats would not yield very good results
for DVD production these days.
If you must produce a DVD based on existing footage, you can't always have
the luxury of picking the ideal videotape format to work with. If you can
obtain an original in the above formats, that's great. But you may be forced
to work with a less desirable format. D2 and D3 are composite digital formats
that produce very good quality. But because all the color and luma signals
are mixed into a single one, you lose some of the advantages of DVD's component
signals. Even thought a DVD can still output component, the signal will
still be the original composite as it was encoded. A step down in quality,
but still acceptable, is one inch videotape. This analog format offered
very high quality at the time and was widely used as a master storage medium.
Like D2 and D3, it is also a composite format.
If you are forced to work with ¾" U-matic, S-VHS, Hi-8, 8mm or VHS, you
will end up with an inferior looking DVD, no matter how careful you are.
These formats are very noisy and the colors don't look that great. They
should only be utilized as a source for a DVD if there's absolutely no other
option. If a client approaches you with one of these formats as source material,
make sure that you explain ahead of time that the resulting DVD will not
look that great in order to avoid future headaches. |
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