[opendtv] Re: New DVDs already sparking copy-protection confusion
- From: "Kilroy Hughes" <Kilroy.Hughes@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 28 Feb 2006 16:04:34 -0800
Kilroy Hughes
Sr. Media Architect
Digital Media Interoperability Team
Microsoft Corporation
[JS] He he, somewhere down there somebody is suggesting that 540p is a=20
resolution that is inferior to 1080i ! ;-)
[KH] I won't tell them if you don't.
[JS] I should hope that a movie is put onto a DVD (or HD successor) as=20
real 24p, and that it is up to the player to convert this to 30i,=20
60p, 72p, whatever you want. This could be done as perfectly as you=20
want it to be. Are you saying that this is not (yet) true?
[KH] Progressive encoding is illegal on DVD-Videos.
Progressive_sequence=3D0 is required, and only 30Hz or 25Hz frame rates
allowed. There has been a long battle to change production practices
and tools to support consistent and invertible telecine so 24P could be
tunneled through 30i transport streams. Accurate 24P cadence in 30i
syntax was the exception for most movies for the first few years of DVD,
but is now the rule.
I'm afraid it will take more than sharpness filters on playback to
restore the missing MTF thrown away in optics and CCD imagers that are
targeting interlaced display. It's a one-way entropy arrow. I hope
1080P24 encoded as 1080i30 will be treated as frame content, not field
content; and only flicker filtered by displays that are dumb enough to
separately refresh even and odd lines, draw them in raster patterns on
non-persistent displays, etc.
BD format now allows 24P encoded Transport Streams. HD format doesn't,
but it identifies 24P encoded as 30i to allow accurate decoding to 24P.
"Advanced Content" playback mode in HD DVD-Video uses a Playlist, which
is the XML equivalent of a musical score that controls synchronization
and navigation of multiple audio and video streams and Applications on a
common timeline, and it provides video attribute metadata that tells the
playback system the true nature of each video source. For instance, it
will tell you a video Clip was captured at 24P (although coded as 30i),
and the active content is a 4:3 rectangle of specified dimensions in the
encoded 16:9 image (surrounded by black or whatever). The presentation
engine and presentation applications can then decode it accurately as
24P, frame it full screen on a 4:3 display, or use whatever framing,
scaling, and cropping the author and user agree on for 16:9 display.
Composition frame rate of the Primary and Secondary video streams,
graphics, animation, etc. can be alpha blended at a frame rate
appropriate for the refresh rate and "signal" format negotiated between
the player and display. That might be 1080P24, 1080i30, 720P60,
1080P60, etc.
[JS] It's not that simple. Some monitors will perform well at only a
single=20
refresh rate, usually 60 Hz. Some will even go free-running if you offer
anything else than that. Be very careful about this...
[KH] Computer "multisync" monitors typically support and report dozens
of VESA image and refresh combinations, and the computer is forced to
pick one of them so it can't go out of bounds. It's normal to find one
or two megapixels refreshed at 100Hz or more with VGA interconnect and
CRT monitors. =20
More computer monitors are sold than televisions, but I've always heard
lots of cost, brightness, power supply, flyback transformer, etc.
reasons why CRT TVs couldn't deviate from the righteous path of 30i. Of
course that changed the year 480P DVD players came out, then additional
HD modes, and now that entirely different flat panel and micro display
technologies rule, I'm expecting monitors to be able to "multisync" or
not "sync" at all to the input format, and handle their own refresh as
necessary for the display technology. =20
For instance, a display should be able to signal a 1080P24 EDID, accept
the 1080P24 movie or TV content in its native glory, and then update
display pixels at 72Hz with brightness pulses (like triple shuttered
film) or motion interpolated updates of only changed pixels, etc. As we
move to HDMI as the only HD player output, there isn't even an option to
negotiate an interface/display mode the monitor doesn't support.
Different display technologies have different characteristics, and I
think there will be advances in motion representation that won't depend
on changing the 24Hz capture and interface rate or reshooting the
Hollywood and TV film archives. That is unless everything is locked to
a 60Hz refresh and that is forced on the interface rate by some need to
repeat a history that is now out of context.
-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]
On Behalf Of Jeroen Stessen
Sent: Monday, February 27, 2006 01:52
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: New DVDs already sparking copy-protection
confusion
Hello,=20
Kilroy Hughes gave a very interesting answer:=20
[JS] >> So my question is: is doing only low-pass filtering a sufficient
>> implementation of this down-ressing, or is the actual sample-rate
>> conversion
>> with associated risk of aliasing and rather permanent loss of higher
>> frequencies mandatory ? What would be an acceptable low-pass filter,
if
>> at all acceptable?
[KH] > I don't recall the AACS license details, but I think filtering is
> adequate. The resolution limit is 960x540, so that will look better
> than 720x480 DVD-V scaled up to HD. (Especially because DVD video has
> its vertical resolution reduced below 480 lines for interlaced
display.)
He he, somewhere down there somebody is suggesting that 540p is a=20
resolution that is inferior to 1080i ! ;-)=20
[JS] >> I hope you mean 480p60, i.e. it has been de-interlaced to 480p24
>> using 3-2 pull-down reversal, and then up-converted to 480p60 again
by
>> using frame repetition in the same 3-2 pull-down sequence.
[KH] > Yes, 480P60 on a settop player. Your process description is a
> little optimistic though.=20
> In a settop player, an unknown mix of 24P and 30i source, 30i
> subpictures, menus, etc. is sent from the decoder to a deinterlacer
chip
Duh ! That is the situation for a TV, that it has to accept any=20
unknown format. I sincerely hope that the situation for a settop=20
player (or a player application on a PC) would be more favorable !=20
I should hope that a movie is put onto a DVD (or HD successor) as=20
real 24p, and that it is up to the player to convert this to 30i,=20
60p, 72p, whatever you want. This could be done as perfectly as you=20
want it to be. Are you saying that this is not (yet) true ?=20
> The PC playback approach with known telecine content is to ignore the
> repeat field flags and decode to 480P24, scale, then refresh at some
> arbitrary rate; although people in the know use 72P. Field
> "deinterlacing" is simple and perfect and no 3:2 motion judder.=20
Aha, now you're talking. And advertizing for Microsoft. ;-)=20
> It is unfortunate that actual vertical information is typically=20
> much less than 480 lines because it has been captured and/or pre-
> filtered for interlaced display.=20
But that is easily corrected with a fixed vertical sharpening.=20
> A PC decoder typically has to play guessing games based on the=20
> pattern of Top/Bottom repeat field flags to decide whether it is=20
> seeing telecine 24P coded as 30i, or 30P coded as 30i, or format
> converted 25i at 30i, or off-speed 30i, or regular 30i, etc.=20
But then we're not talking about a regular movie, right ??=20
> The actual source format is well hidden by the MPEG 30i stream=20
> because video used to be slaved to CRT refresh rate. The PC decoder=20
> has the advantage of the repeat field flag metadata (lost once it is=20
> decoded to a 30i video signal), and the flexibility to decouple the=20
> decoding rate from the display rate (computer controls the refresh
rate,=20
> not the monitor).
It's not that simple. Some monitors will perform well at only a single=20
refresh rate, usually 60 Hz. Some will even go free-running if you offer
anything else than that. Be very careful about this...=20
Best regards,=20
-- Jeroen
+-------------------------------+---------------------------------------
---+
| From: Jeroen H. Stessen | E-mail: Jeroen.Stessen@xxxxxxxxxxx |
| Building: SFJ-5.22 Eindhoven | Deptmt.: Philips Applied Technologies
|
| Phone: ++31.40.2732739 | Visiting & mail address: Glaslaan 2 |
| Mobile: ++31.6.44680021 | NL 5616 LW Eindhoven, the Netherlands
|
| Skype: callto:jeroen.stessen | Website:
http://www.apptech.philips.com/=20
|
+-------------------------------+---------------------------------------
---+
=20
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