Mark Wagner wrote:

> MPEG-1 and MPEG-2 are *not* simply different versions of the same standard.

correct.

> They are two *different* formats, designed to solve *different* problems.

hmm.

With the reference MPEG-2 codec from mpeg.org (or with png support from my place)
if i throw a switch, it disables some features, sets some limits, and generates
a perfectly legit MPEG-1 (granted it has too much compression, but it is legal)

The formats are almost identical; the difference lies in the compression
algorithms.

> MPEG-1 is optimized to compress solid-image video like what you get on a
> computer, 

MPEG-1 is optimized to compress JPEGs, which are not best suited for solid-image
video.  It comes from MJPEG, or multi-jpeg.  It was designed for network transmission;
hence the emphasis on the less than 1.8Mb bitrate, which is coincidentally 
near the rate of a T-1.

(Specifically, ALL MPEG formats are optimized to figure the difference between 
2 jpeg frames.  Basically, send frame 1 as a jpeg (very small); send frame 2 
as the difference between frame 2 and frame 1)

Solid image video would be like .FLI or .FLC or ani-gif.

> while MPEG-2 is optimized to compress interlaced-image video such
> as is found on television broadcasts.  

Interlacing is an option.  MPEG-2 was designed for HDTV, with wacky aspect ratios
and *lots* of data.  The HDTV boys took so long to get their act together that
MPEG-2 was (compatibly) rebuilt for lower end work.  It just happened to be perfect
for 
DVD (with a little encryption thrown in).  Some of the higher end MPEG-2 features
are still theory (AFAIK) like 30+ Mbps and 4:4:4 encoding.

> You could use MPEG-2 to compress your
> IRTC entry, 

Imagine "Antz", "Toy Story" or "ST:TNG the battle" on your 35" TV off of DVD and 
substitute your IRTC entry, yeah that would suck.

> or MPEG-1 to compress a videotape, but the compression would be far from ideal.

See some of the work from alt.binaries.multimedia.  If you're not into the "erotica"
end,
try to find the awesome Super Bowl commercials from last year.

I've watched a lot of broadcast TV (and tapes and DVD) over MPEG-1 [1].  6 months of
"Oprah"
and "Judge Judy" :)  I've seen "The Matrix" and "Antz" and "Total Recall" [2] over 100
times 
(but never more than 5 minutes at a pop :( )

MPEG-1 is not that bad.  In fact, one of the MPEG-1 design goals was to have the
bandwidth
of VHS video tape.

If you use a hardware encoder rather than some reference software encoder like cmpeg 
or mpeg_encode, then its hard to tell the difference between VHS and MPEG-1 TV output.

> Mark

--
[1] I was designing software to drive MPEG-2 hardware.  In the office, there were
about
    15 "channels" of multicast MPEG-1 running through the network at all times.

[2] There was much rejoicing when the DVDs came into the office because no longer
would
we have to watch afternoon TV or worse, remember to change tapes; just put on
"repeat".
Actually, the thing i have watched the most is the boot screen from my Sony DVD
player.
'Don't care what it plays, as long as its a solid video signal :)  I have gigabytes of
Sony DVD boot screen NTSC->MPEG-2 encoded on my hard disks. :)

dik

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