[opendtv] Re: New DVDs already sparking copy-protection confusion
- From: Jeroen Stessen <jeroen.stessen@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 20 Feb 2006 13:12:29 +0100
Hello,
Kilroy Hughes:
> The comment about degraded picture quality is probably a reference to a
> video publisher's option to set a flag that forces players to "down res"
> their video output to quarter HD resolution over unprotected outputs,
> such as YPbPr and VGA and DVI.
Perry is very familiar with picture improvements, and less so with
scaling,
but his point is one that I had not seen before. It may be a valid point.
But let's talk about this "down-ressing". Let's say we receive a 1080p
signal,
and for lack of protection it must be down-ressed to 480p. Then we connect
it
to a 1080p display, so it must be up-ressed again to 1080p. The net effect
is
that the signal has only been low-pass filtered to somewhere around 360
cpw
and 240 cph. 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 ?
> DVDs are always decrypted and decoded in the player so image
> correction/conversion can be applied before output encryption is
> applied. Most DVD-V players output 480P30 theses days thanks to
> deinterlacer chips, and in some cases output scaled 720P and 1080i.
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 ?! There should never be a
signal with a 30 Hz frame rate, except an original 480i30 signal maybe.
> People are aware that HDMI encryption can be broken, but
recording/encoding
> the > 1Gbps video stream, or viewing on a legacy display aren't high
> priority threat models.
A representative from Silicon Image once explained to me that HDCP was
meant
"to keep honest people honest". The fairly weak encryption (which was not
too
weak at that time, but you could extract the signal after the HDCP
decrypting
circuit) in combination with the relative uselessness of an uncompressed
signal make it unattractive enough for honest people who might want to
hack it.
The only serious threat that I can think of is that one would set up
DVI/HDMI
splitters to supply an entire building with pictures from a single
decoder.
Encrypting the signal to a single display (key) would prevent that.
> Realtime HD capture/encode of analog signals is a somewhat bigger risk
and
> may not have circumvention barriers.
Why is that a bigger risk, if it is (slightly) more difficult than
stealing
the HDMI+HDCP signal, and it adds analog noise and jitter too ?!
And this is easily made less attractive with watermarking. E.g. see:
http://news.bbc.co.uk/1/hi/entertainment/4724584.stm
<quote>
Man charged over Oscar 'piracy'
A man accused of uploading a copy of the biopic film Walk the Line has
been
charged with copyright infringement.
(...)
Assistant US Attorney Brian Hoffstadt said a digital watermark showed the
copy of Johnny Cash biopic Mr Ochoa is accused of posting on the internet
was a "screener" copy sent to an Academy voter.
He added it had allegedly been taken before it reached the intended
recipient.
(...)
<unquote>
It's similar to how they don't force installation of speed limiters in
cars.
They just take your picture when you speed, and send you the bill later...
Best,
-- Jeroen
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