[opendtv] Re: New DVDs already sparking copy-protection confusion
- From: Jeroen Stessen <jeroen.stessen@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 27 Feb 2006 10:52:20 +0100
Hello,
Kilroy Hughes gave a very interesting answer:
[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
resolution that is inferior to 1080i ! ;-)
[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.
> 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
unknown format. I sincerely hope that the situation for a settop
player (or a player application on a PC) would be more favorable !
I should hope that a movie is put onto a DVD (or HD successor) as
real 24p, and that it is up to the player to convert this to 30i,
60p, 72p, whatever you want. This could be done as perfectly as you
want it to be. Are you saying that this is not (yet) true ?
> 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.
Aha, now you're talking. And advertizing for Microsoft. ;-)
> It is unfortunate that actual vertical information is typically
> much less than 480 lines because it has been captured and/or pre-
> filtered for interlaced display.
But that is easily corrected with a fixed vertical sharpening.
> A PC decoder typically has to play guessing games based on the
> pattern of Top/Bottom repeat field flags to decide whether it is
> 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.
But then we're not talking about a regular movie, right ??
> The actual source format is well hidden by the MPEG 30i stream
> because video used to be slaved to CRT refresh rate. The PC decoder
> has the advantage of the repeat field flag metadata (lost once it is
> decoded to a 30i video signal), and the flexibility to decouple the
> decoding rate from the display rate (computer controls the refresh rate,
> not the monitor).
It's not that simple. Some monitors will perform well at only a single
refresh rate, usually 60 Hz. Some will even go free-running if you offer
anything else than that. Be very careful about this...
Best regards,
-- Jeroen
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| From: Jeroen H. Stessen | E-mail: Jeroen.Stessen@xxxxxxxxxxx |
| Building: SFJ-5.22 Eindhoven | Deptmt.: Philips Applied Technologies |
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