[vorbis] Video codec

[Ralph Giles]

On Mon, 11 Sep 2000, Chrissy and Raul wrote:

> >Totally agreed. Let's start making list and try to agree upon it?

I assume these are for purposes of comparison and guidelines for common
source types, rather than requirements. I was hoping we also "already
agree" to allow arb. frame size and rate. One of my pet peeves with the
DVD spec is the way they include the letterbox mask in the frame they
compress, just to keep things within the spec'd size and aspect ratio.

> Frame Rates:
> 
> - 15 fps (half 30 fps)
> - 24 fps (Film native rate.  I heard that in Europe 24 fps movie DVDs are 
> presented at 25fps which make them end sooner, good, more time for the 
> family, is this true?)
> - 30 fps

Likewise, we're not worrying that 30 fps isn't really 30 fps in NTSC
video?

I'd also suggest 16 fps for early cinema, and 60 for action sequences
(ask someone who plays first person shooters). Rates of 8 and 12 fps are
sometimes used for animation.

> SIF (320x240 resolution)
> [...]
> QSIF (160x120 resolution)

We also need other frame sizes for film. Common aspect ratios are:

1.33:1  (4x3)
1.78:1  (16x9)
1.85:1  (US standard for 'just ordinary movies')
2.35:1  ("cinemascope")

Here are some examples based on multiples of 240, by way of example:

vert.	x1.33	x1.78	x1.85	x2.35
240	320	426	444	564
480	640	854	888	1128
720	960	1280	1332	1692
960	1280	1706	1776	2256

Note that block-oriented codecs like mpeg want the sizes to be multiples 
of 8, 16, or 32, of which every few of these qualify. For a given aspect
ratio one can usually find something though. For example, the "Lord of the
Rings" trailer (quicktime) is available in 240x104, 320x136, 480x204, and
640x272. All divisible by 8 and all but the smallest at 2.3529:1.

As Monty pointed out, the proposed wavelet codec doesn't care about
blocks. I don't know anything about the proposed non-power-of-2 transform
though. Are things like small prime factors important like with the fft? 

The US HDTV standard also suggests some standard frames:

640x480   (4x3)
1280x720  (16x9)
1920x1080 (16x9)

All but the largest support 24,30, and 60 fps (actually 60/1.001).

IMO we should be planning to target content production and a replacement
for DVD-video as well as web streaming. That means large formats. The
acknowledged digital-equivalent vertical resolution of 35mm film is 4k
lines (these days; that's about equivalent to the 70mm epics of 25+ years
ago). Most special effects work is done at 2k lines and some folks claim
to see the difference. That's not to say you always get that, of course:
it depends on film stock, exposure, lens quality, development, etc. At
some point, you're just resolving the grain. OTOH, rumour says the new
"digital film" camera being used to shoot the next "Star Wars" are only 1k
lines (960, I think) and they're still having to be more careful with set
painting because they give sharper detail than film.

See this recent slashdot article for further comments:

http://slashdot.org/article.pl?sid=00/09/11/1710204

Speaking of square pixels, the advantage is obvious to most software
people, but we'll need to be ready to defend this one. One thing I didn't
realize is that effectively *all* 35mm film work uses an anamorphic
(cylindrical) lens to squeeze the director's chosen aspect ratio onto a
standard-sized area of film. (The process is reversed in projection.) So
people are used to this, and from the point of view of hardware
implementations, it makes a lot of sense to have a fixed frame-size plus
(even arbitrary) horizontal scaling.

> I am using three scenes for the video compression experiments: hockey, 
> mongolian rock concert, mongolian flag and plaza.

Do you own the copyright on these clips? Would you be willing to make them
available in uncompressed form (on the net, or mail someone a cd) so we
can make a start on a test suite?

Cheers,
 -ralph


--
giles at ashlu.bc.ca

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