Businessweek reports that CinemaNow has delivered the Holy Grail of the online movie business: a mainstream movie (although, it must be said, not a very good movie) that consumers can purchase for $10 and burn to a DVD that can be played on an ordinary DVD player.
Well, sort of. BusinessWeek mentions in passing that they licensed technology “from a German company” to copy-protect the DVDs. That made me skeptical, as the technical problem involved was quite challenging. As has been discussed on this site before, the copy-protection on DVDs works by putting the encryption keys for the DVD in a part of the disc that can’t be written to on the type of DVD-R media that’s available to the general public (known as “G” media). That means that if a PC tries to copy a DVD, it can read the keys, but it can’t write them to the new disk.
But what that really means is that home computers can’t create any encrypted DVDs that will play on DVD players, because the only encryption scheme those players support is the one that requires “A” media, which isn’t available to ordinary consumers. All a PC can do is generate an unencrypted movie. And that, Hollywood believes, would be an unacceptable piracy risk. So, I thought, this magical German technology must be awfully sketchy to do what it claims to do.
It turns out that Cory Doctorow is way ahead of me on this issue. Back in August, an anonymous engineer examined the technology and had this to say on Boing Boing:
The system is based on the deliberate introduction of errors caused by Digital Sum Value (DSV), a sum that represents the ratio of land to pits on the surface of the DVD. The DVD spec notes the possibility of DSV errors and instructs implementers to take care to avoid them, as these errors can cause a host of problems with reading and playing discs.
My source notes that the introduction of DSV errors is indiscriminate and uncontrollable–the multitude of possible combinations of DVD burners’ chip-sets, blank media, and other variables means that any attempt to introduce DSV errors will produce unpredictable outcomes.
The engineer tried burning Burn-to-DVD discs with a variety of test-bench equipment and found that many of his burners failed entirely, and of those that succeeded, many produced unplayable, error-ridden discs.
For the “successful,” marginally playable discs, the news is still bad, since those discs will already be at the limit of their players’ error-correction threshold, so that minor scratches and dust would render them useless…
My source sums it up neatly in this outraged paragraph: “I’m against people being fleeced by this kind of crap. How can you sell someone content on media that is so heavily compromised, especially on a format that so heavily relies upon its error correction system to maintain playability? It’s mind boggling!”
What they’re doing, in effect, is attempting to introduce the quality-degradation characteristics of analog media into a digital format, in the hopes that the first-generation copy will be readable, but that subsequent generations will be rendered illegible. This is, to put it bluntly, a really stupid idea. And it’s not a new idea either. As Ed Felten has written, the same types of tricks have been tried with CD, with lousy results:
Passive protection exploits subtle differences between the way computers read CDs and the way ordinary CD players do. By changing the layout of data on the CD, it’s sometimes possible to confuse computers without affecting ordinary players–or so the theory goes. In practice, the distinction between computers and CD players is less precise. Older generations of CD copy protection, which relied entirely on passive protection, proved easy to copy in some computers and impossible to play on some CD players. For these reasons, copy protection vendors now use active protection–special software designed to block copying.
The really irritating thing about all this is that it’s really quite pointless. Apple’s iTunes Music Store allows you to burn completely unprotected CDs of the music you purchase, and the music industry doesn’t appear to have regretted allowing that. DVD-ripping software like Handbrake is widely available to circumvent the copy protection on commercial DVDs, so it’s not like it’s that hard to get unencrypted versions of movies. So what exactly would be the harm of simply allowing the user to burn an unencrypted DVD?
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