[vorbis] Video codec

[Chrissy and Raul]

MPEG-2, at moderate (20:1 [10 Mbps, CBR, 4:2:0] ) to high compression ratios 
(40:1 [5 Mbps, CBR, 4:2:0] ), creates several kinds of artifacts.  The most 
noticeable ones are three:

1) Blocking noise (blocks that are 8 or 16 pixels square)
2) "Mosquito" noise (irregular dots around sharp edges, like letters or 
numbers)
2) Low-level DCT noise, crawling dots on flat surfaces

The first is of spatial nature, still/individual images have it.  The second 
is spatial and temporal (still and moving images have it).  The third can 
only be detected with moving images as flat surfaces move.

Only with Hockey or Basketball you get blocking noise at 10 Mbps, and only 
sometimes.  The three are visible at 5 Mbps.  This is assuming good IBP 
coding.

Color changes and blurring (unless very obvious) are harder to detect 
without side-by-side comparisons.

RAUL LOPEZ

>From: Tom Bishop <Tom at Truly.nu>
> >
> > > the MPEG effects were not
> > > that noticable on a 27" tube, but when played on a 43" projection 
>system
> > > suffers very noticably.
> >
> > Which the best noticable degradation: Ringing? Blocking? Blur? Skewed
> > areas? In the colors or in the luminance? I'm sorry, I haven't seen the
> > tivo in Europe yet.
>
>I have replayTV.. I would say "Blocking" ..though I do not have that
>much understanding of terminology, there are prominent blocks that appear
>during action.. still shots look reasonable.
>
>Regards,
>Tom
>
>
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