Re: Ripping DVDs ... and MythTV

["Derek Martin-9" <user=7@nabble.blu.org>]

 On Fri, Nov 23, 2007 at 01:09:41AM -0800, Kristian Erik Hermansen wrote: 
> http://rg03.wordpress.com/2007/01/14/backing-up-dvd-movies-under-slackware/

This document points to the Gentoo DVD backup howto, which mentions 
that dd usually works.  As you point out, most DVDs are encrypted, 
so dd should usually fail if you are correct, often enough that it 
would not even be worth trying or mentioning in a document, or at 
least mentioning that it would only work when the disc is not 
encrypted.  Instead, the document says it ususally works.  When it 
doesn't, you get I/O errors, which Jarod already explained:   

  http://en.wikipedia.org/wiki/ARccOS_Protection

ARccOS != CSS.  A relatively small percentage of discs will have been 
encoded with this protection, since it was a more recent development, 
and has been discontinued due to hardware incompatibilities. 

The existence of libdvd* on a system does not mean that they have been 
used.  Since the dd command is not linked against those libraries, 
then it has no means of making use of them -- barring support built 
into the kernel, which I'm sure Linus would never allow -- so 
basically any successful dd of an encrpyted DVD on any system proves 
that CSS does not prevent dd from copying DVDs. 

> > The key is that CSS considers the "disc content" to be the movie, 
> > rather than the raw bits.  So yes, authentication needs to happen 
> > before you can play the movie.  It doesn't need to happen before you 
> > can read the raw bits. 
> 
> I still believe you are incorrect here, so if you could please provide 
> valid support of your statement, or some proof of your claim, I would 
> be quite interested because it contradicts everything I have seen and 
> known about encrypted DVD videos since 1996... 

Besides the above, a quick search turned up a few: 

http://www.lemuria.org/DeCSS/decss.html

Mentions that DVDs could be bit-wise copied, and sites a 
Note that at the time deCSS  was written, DVD burners were not 
available, so it was not possible to burn a full DVD using comodity 
hardware and media at the time.  It was the writing process, not the 
reading process that caused the difficulties referenced in this 
document.  (The document references an interview on CNN which 
clarifies the time line of the availability of DVD burners): 

  http://transcripts.cnn.com/TRANSCRIPTS/0001/11/st.00.html

Jon Johansen (in 2000) mentions that copying was possible even with 
the encryption in place. 

  http://archives.cnn.com/2000/TECH/computing/01/31/johansen.interview.idg/

Article mentions (in 1999) that it was always possible to copy the encrypted 
DVD to a hard drive. 

  http://findarticles.com/p/articles/mi_m0FXG/is_12_12/ai_63973528

And also Jarod mentioned that he actually does this. :) 

Technically, I haven't "proven" anything....  This is good enough for 
me, but if one were so inclined, it shouldn't be too difficult to 
test.  You just need a few known encrypted DVD that were released 
before 2005 or so (so it will be certain not have ARccOS on it) and a 
linux system with a dvd drive in it.  If you want to be thorough, 
remove libdvdcss and libdvdread from your system first.  You can try 
to play the DVD in Totem (or whatever) once libdvdread and dvdcss have 
been removed, to verify it won't play without them.  The reason I say 
you need a few DVDs is that dd is not terribly fault-tolerant... 
scratches or bad spots on the disc (legitimate ones) will cause the dd 
to fail with an I/O error.  Using noerror might help, but the disks 
should be in as good condition as possible.  If any succeed, CSS does 
not prevent dd from being able to rip DVDs. 

-- 
Derek D. Martin    http://www.pizzashack.org/   GPG Key ID: 0xDFBEAD02 
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