A look at content scrambling in DVDs

(mathweb.ucsd.edu)

22 points | by rvnx 2 days ago

3 comments

  • hedora 1 hour ago
    This is a fun rabbit hole to walk down.

    You might have noticed that streaming is getting worse (more expensive, less selection, more ads, more fragmentation). For me, they crossed a breaking point, where I decided I'd just find something more convenient.

    So, I went down to the local record store, where they have 10,000s of DVDs and Blu Rays in stock; many for $1 (DVD), $2 (BluRay), most under $5-10, and a few gems for $20-30. The prices are for a mix of new and used DVDs; some new DVDs are over-printed, and cost $1.

    Problem half-solved. I looked around to figure out how to play these anachronistic shiny disks on my TV, and eventually settled on a USB BluRay RW drive (I guess you can get rewritable BluRays!)

    I never figured out how you're supposed to actually use that drive to play movies. Instead, there's DeCSS from the article, then something comparable for BluRay. For the "easy" decryption, you end up downloading per-disk decryption keys for every disk ever printed.

    For the more advanced stuff, they have this giant Java Rube Goldberg machine that xors glitches into the video stream. This gets applied at the factory, and then (on some hardware I guess you can purchase?) again via some complicated JVM stack that was originally meant to just render the scene selection menu.

    [spoiler alert]

    The easiest way to play those BluRays back is to just download the output of the Rube Goldberg machine. At some point the industry realized that scheme was dumb, so there's a finite set of glitch masks. The whole dataset for all BluRays that will ever be produced with this scheme is a few GB.

    You might think that when I say "play", I mean "transcode + pirate", but it turns out that's not particularly practical. BluRays are multiple GB, and already compressed with codecs that are competitive with modern ones, so they don't shrink down like DVDs unless you're willing to lose a lot of quality.

    So, yes, we have a growing collection of physical media. I target 20-30 movies / $100 when I go to the store. It's grand.

    • stevekemp 4 minutes ago
      Same story here, I can be used films on DVD for €1 at many charity shops. Boxed sets of TV shows are €2-5 depending on size/popularity.

      The only downside is that I've noticed that the used DVD sections are definitely getting smaller. I guess fewer people are donating their collections these days.

      I've bought a couple of DVD sets from Amazon, used, but the prices there aren't so competitive. Still it's nice to have physical media, with real/original soundtracks.

    • recursivecaveat 35 minutes ago
      I used to not be a physical media person. I have found that it makes it a lot easier for me to start and to finish things though. The fact I have to actually get up to swap the disk out if I want a distraction helps focus the attention span haha.
    • MathMonkeyMan 1 hour ago
      How many GB? I see "bluray rip" mp4 files on torrent index sites, which I assume have been aggressively recompressed, but there are three size tiers in the "1080p" category: 2-3GB, 7-10GB, and 15+GB.
      • dddgghhbbfblk 41 minutes ago
        You want to search for BDMV for full disc images, or for remuxes which are uncompressed video and audio streams, if you want to get a sense for the size on disc. Typical Blu-ray images will be from 20-40ish GB.
  • janci 1 hour ago
    How was CSS supposed to protect against copying the encrypted data? We should not need to decrypt the video to duplicate the disc.
    • wmf 1 hour ago
      Keys were stored on an area of the disc that wasn't writable on DVD-Rs so you couldn't copy the whole disc.
    • dddgghhbbfblk 36 minutes ago
      It's implemented in drive firmware, so the drive will refuse to read protected sectors without authentication.
  • charcircuit 1 hour ago
    >He hadn't pirated anything, only made a program to view his DVDs in Linux.

    He released a tool for circumventing a protection measure. While already illegal to do in America, it wasn't made illegal in Norway until less than 2 years later.