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Re: [ProgSoc] Calling all savants



On Wed, 16 Mar 2005, David Edney wrote:

> which weigh in at 700mb (twice the old size), and while I've not downloaded
> one to check, I gather these are 1080i (or maybe made into 1080p, who knows).

You really think?  1920x1080 is incredibly difficult to decode realtime in
MPEG-4.  But, I'm happy to be proved wrong (and I don't go around looking
for these things, so I wouldn't know, would I?)

1080i ... some myth-busting.  It's often used in segmented-frame format.
So what's often broadcast in 1080i60 or 1080i50 is in fact 1080sF24 or
1080sF25.  This makes it equivalent to 1080p24 or 1080p25 because the
broadcast MPEG-2 encoding won't find interlacing in the macroblocks and
treats the frames as a single field.  Thus, invalidating all the arguments
about 576p for film content in one fell swoop.

Another peculiar thing ... the advantage of MPEG-4 over MPEG-2 erodes as
you move into higher resolutions.  Part of this may be to do with pixel
densities at the point of viewing;  but it is incredibly difficult to
reduce the bitrate by merely 50% and keeping the same picture quality when
dealing with HD footage.  There's no obvious reason for this so it may be
the quality of most SD footage is suboptimal already.

700MB files would ring in at about 2Mbps instead of the usual 1Mbps.  That
gets you to about 1280x720 at film frate rates.  Or, you can do 1024x576
at TV frame rates.

Since I don't find 700MB a big deal (I'd rather swap DVD-R discs), it's
better to stick with 13Mbps, which fits one Enterprise MPEG-2 episode on a
single disc.  This gets you 1080p =and= makes it viewable on a mid-range
CPU.

CK.

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