Exclusive Macrovision describes version 7 of its CDS-300 copy protection system as a major step forward in keeping P2P users' hands off copyright content for which they don't have the distribution rights. Having seen a demo of the alpha release, which performed as advertised, we were nonetheless pleased when a copy of the latest beta version turned up in The Register's mailbag.
Since the alpha release, Macrovision has shifted the system's focus away from tinkering with the contents of the CD Audio session - a technique it calls 'passive protection' - and toward smarter use of multiple disc partitions, or 'session protection'.
That should help appease hi-fi purists concerned that the addition of deliberate errors into the audio datastream reduces the effective lifespan of the disc. CD playback requires a hefty level of error correction to yield the sound clarity for which the medium is famous. Adding noise to the audio content may fool ripping software but, say some observers, it also further taxes CD players' error correction systems, which may already be having to cope with scratches and grease on the disc's surface.
Beyond a certain point, the theory goes, the error correction mechanism will not be able to cope, so by adding errors to the datastream, Macrovision is reducing the amount of damage a disc can take before it becomes unplayable. We'd say disc buyers should take better care of their CDs, but Macrovision has nonetheless scaled this element of its copy protection scheme right back.
Indeed, we were able to duplicate the CD Audio part of the disc - the Red Book session - and there was none of the irritations such deliberate errors are supposed to induce in computer-made copies.
But back to session protection. Essentially, this is the old technique of hiding multiple disc sessions from systems for which those sessions are irrelevant. When CDs might once have incorporated data as a 'track 0', which would have shown up on a CD player but played as either white noise or silence depending on the sophistication of the hardware, multi-session mastering allows, say, the Mac OS partition to be hidden from Windows users and vice versa - and for both to be ignored by a CD player. Multiple sessions are now part of the CD spec, courtesy of the so-called Blue Book, which covers Enhanced CDs and was developed by Philips, Sony, Microsoft and Apple.
On the office Windows XP box, the CD Audio session is thus hidden from inspection - only the PC-compatible session appears in the My Computer folder. Holding down the Shift key prevents the session from auto-running, but double-clicking amounts to the same thing: Macrovision's own Flash-based applet is launched and instances Windows Media Player (WMP) for playback. Session protection ensures you can't access the CD Audio even if you do hold the Shift key down, at least not through Windows itself.
Exploring the disc session reveals the 192Kbps WMA files offered to PC users as an alternative to the Red Book tracks, along with the various DLLs and CD burning code - of which more later.