Nuts & Volts

VideoDigitizerChoices
for an edit to re-render back to disk.
The MPEG converter allows you
to read in AVI, DV-AVI, MPEG-1/2,
ASF, WMF, DivX, and DAT files. The
converter can output in seven MPEG-
2 formats and seven MPEG-1 formats,
each with customizable parameters,
including variable bit rates.
The PVR-Plus CD and DVD burning
program is functional, but weak on
features. For instance, it does no autoconversion,
expecting only one type of
file for each of the formats: DVD, SVCD,
or VCD. You must record everything in
the right format, or use the convert
program first. It can generate menus
for DVDs, but not for VCD or SVCD.
PHOTO 5. The smaller control window can bring up any of four separate
programs. Video editing is shown here as the second program.
with even more options than the
capture software. I particularly liked
the DivX plug-in’s option to specify a
file size, and let it choose the bit rate to
match. At times, the PVR-Plus editor
added a few extra frames to the beginning
or end of a cut, which was
frustrating after waiting many minutes
Forced to Choose —
Resolution or Bit Rate
Power Producer 2 has only three
DVD qualities (HQ, SP, LP), and specific
parameters are fixed. Resolution of the
SP setting is 352 x 240, and I initially
Table 1 shows a number of video
data stream formats. This list is not comprehensive,
but rather reflects what I
found from multiple manufacturers as I
shopped for video capture hardware.
Notice there are several standard resolutions,
encoding schemes, and bit rates
that keep showing up, but also notice
that some names mean different things
when used in context of different companies’
products.
I included a number of Plextor formats
in the table even though I didn’t use
their hardware because they offer free
sample video clips for comparison, available
at www.plextor.com/english/prod
ucts/ConvertX2advancedtechspec.htm
Language Glossary
Identifying exactly which format
you’re talking about sometimes gets blurry.
If you refer to a “DVD format,” 99% of
the time you’re implying MPEG-2 encoding.
(There is room in the official specification
for MPEG-1.) The reverse isn’t true:
only some combinations of MPEG-2 play
successfully on DVD players. You can go
up to about 9 Mbps and still be “legal” for
DVD players, but if you average much
above 5 Mbps, a standard length movie
won’t fit on a single DVD disk. Some
MPEG-2 resolutions are optimized for
computer display, such as the 640 x 480
resolution listed in the table. If you’d like
64 April 2006
VIDEO FORMATS
a technical overload of what each term
means, there’s a comprehensive glossary
at www.afterdawn.com/glossary
TV Presentation vs.
Computer Screens
Standardized resolutions for movie
viewing are SIF (352 x 240), F-D1 (720 x
480), and 1/2-D1 (352 x 480). For comparison,
all NTSC televisions are (... x
525), with horizontal resolution specified
at several hundred up to a thousand
dots per line. The horizontal resolution
isn’t an exact number, but rather more of
an analog bandwidth of how fast the
electron gun can be modulated.
Unlike computer screens, the pixel
resolution of a video format doesn’t imply
the aspect ratio. You can think of it this
way: Video formats often use non-square
pixels. What’s really going on is that analog
TV video for each line isn’t naturally
pixels — it’s just a changing voltage that
can be digitized at fast rates to get many
horizontal pixels, or slower rates to get
less horizontal pixels. On the other hand,
the number of lines in each TV frame is
unambiguous. A digitized video file can
declare internally what aspect ratio is to
be displayed, or your video player makes
the choice. Common ones are 4:3 for TV,
and 16:9 for DVDs. I found a decent technical
tutorial at http://members.aol.
com/ajaynejr/vidres.htm
Audio tracks are pretty standardized
on MPG-1 Level 2 encoding at 44.1
kHz or 48 kHz sample rate, although
older stand-alone DVD players may
require LPCM compression. Valid audio
bit rates for non-PC play maxes out at
448 kbps on the DVD format, but most
optical disk video uses less.
Disk Sizes
Lastly, standard disk sizes set some
of the norms. For example, fitting 120
minutes on a 4,700 MB DVD requires 39
MB/min or less, so most commercial
DVD MPEG-2 recordings use this range.
SVCD and VCD formats mimic DVD
behavior (menus, chapter), although the
“legal” combination of video parameters
gives you slightly lower quality for these
formats. Run times are about 30-40 minutes
for SVCDs and 60 minutes for VCD.
Stand-alone DVD players are typically
able to play any of the three formats,
but you can’t mix them. In other
words, storing high quality DVD on a CD
won’t let you store much, but there are
times when I wish I could do this for
short clips. DVD quality on a CD will
play in my computer, but not on my
stand-alone DVD player. If you’d like to
adventure off and try non-standard
combinations of video and/or audio,
www.afterdawn.com/guides will help
get you started.