[vorbis] Video codec

[Jelle Foks]

Tom Bishop wrote:
> 
> > I think if we want to compete based on compression ratio, then we should
> > somehow get at 0.1 bits per pixel or below. A CDROM is approx
> > 650x8=5.2Gbits, so for an hour of video you have 5200/3600=1.44Mbits/s,
> > which would dictate a compression to below approx (1.44/10.3)=0.14 bits
> > per pixel if there is to be any room left for audio etc.
> 
> Tivo and Replay TV encode MPEG at about 1 Gigabyte / hour record time
> (extended play mode).

8000/3600=2.22mbit/s. That is a nice high bit-rate for any half-decent
SIF (360x240NTSC/360x288PAL) MPEG1 'VHS quality' encoders (which use
4:2:0 subsampling, so there's just 180x120 chrominance resolution).
2.22mbit/(360x240x30 pixels) = 3.42 bits per pixel. although SIF 4:2:0
isn't really as good as a modern VHS recorder, not even at long play.
However, at the full broadcast TV image size of CCIR601/656
(720x480x30NTSC), this is only 0.21 bits per pixel, at which rate it is
pretty hard to achieve good video quality with MPEG1 or MPEG2 coding.

> This extended play suffers badly with action.... 

That would indicate they're encoding at full CCIR601/656 resolution,
because I believe that at SIF resolution that should not happen.

> 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.

Cya,

Jelle.

> Regards,
> Tom
> 
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