[vorbis] Video codec

[Jelle Foks]

Tom Bishop wrote:
> 
> Thanx for the description.. ;-)
> 
> Would say blocking noise..
> 
> It is as if there is not enough info to fill in the details,
> so it just paints the block all one color...

One color. If that happens in places where the image really contains
more variation that that, then that's a sign of a pretty 'desparate'
encoder. In that case the encoder decides to discards all higher DCT
component alltogether and encode only the DC coefficient. That would be
a bit rate really too low for the encoder to handle.

> Regards,
> Tom
> 
> ----- Original Message -----
> From: "Chrissy and Raul" <chrissyandraul at hotmail.com>
> To: <vorbis at xiph.org>
> Sent: Monday, September 11, 2000 4:58 PM
> Subject: Re: [vorbis] Video codec
> 
> > 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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