Popular HD DVD Disc Hits a Snag

An anonymous reader writes "Following weeks of headlines touting strong sales for Blu-ray discs, rival next-gen format HD DVD looked like it had its own success story in the making with this week's HD DVD release of the cult hit 'Children of Men.' The disc recieved a stellar review at High-Def Digest, and went on to out-sell the most popular Blu-ray discs on Amazon. But now comes word of apparent incompatibility issues with the Xbox 360 HD DVD player, with some (but not all) consumers reporting that even multiple returns of the disc are unplayable on the format's leading playback device."

Comments

Not just XBox 360 Player that has problems...

[TheNetAvenger]

Not just XBox 360 Player that has problems...

I know it is wild to assume that SlashDot would not mention this part, but it appears that some Toshiba based drives also have problems with this Disc.

PS. I hate the HD-DVD DRM as much as everyone else, but if the DRM was to blame it would NOT be failing at the DRIVE level and would be failing at the player level where the DRM is processed.

Re:What's old is new again

[SirMeliot]

Yep I had that too.

In the UK Woolworths sold a Samsung DVD player which was I think the first sub £200 DVD player you could buy in the high street. They sold a ton of these and were very good about taking them back again when they wouldn't play the Matrix.

IIRC early PS2s didn't care too much for the Matrix either.

Re:Why can't the industry make things compatible?

[illegalcortex]

Is there really a difference in the error correcting codes written to +R and -R?

Yes.
From http://adterrasperaspera.com/blog/2006/10/30/how-t o-choose-cddvd-archival-media/

As I said earlier, DVD-R sucks for data preservation for three reasons: inferior error correction, inferior 'wobble' tracking, and the fact its data writing methods look like an un-needed halfway point between CD-R and DVD+R. The wobble tracking I shall explain first, then the error corrections method, then the specifics of ATIP/pre-pit/ADIP optimum power settings.

For a CD/DVD burner to track where it is on the disc, it uses three things: the 'wobble' of the data track (where it actually wobbles back and forth instead of in a straight line) to tell where it is in the track, the position of the track to tell where it is on the disc, and some additional information on the disc to tell where the track (singular, as CDs and DVDs only have one track, and it is written in a concentric spiral) begins and ends.

This additional information on a CD-R is called the ATIP (Absolute Time In Pregroove), which contains how long the track is, where it begins, what the maximum and minimum writing speeds are, what formula dye it uses, who actually made it, optimum power control settings, and error correction data. The ATIP is stored as a frequency modulation in the wobble itself.

However, since the wobble changes subtly to encode data, it is impossible to use with the small size of tracks DVD requires, as electric noise in the laser pickup and wobbles introduced by the electric motor spinning the disc, these could easily be read as frequency changes in the real track itself.

On DVD-R, they tried to solve the problem with something called 'pre-pits' where spikes in the amplitude of the wobble appear due to pits fully out of phase with the rest of the track (ie, between two spirals of the track, where there is no data). This can be viewed as a simple improvement over CD-R as it makes it easier to track the wobble (since the wobble is constant except for the easy to detect and remove spikes).

Unfortunately, this method as one flaw: due to electric noise in the laser pickup, it would be very easy to miss the pre-pit (or read one that wasn't actually there) if the disc were damaged or spun at fast speeds. The time to read a pre-pit is 1T (roughly .0000000038th of a second), which even for a computer can be easy to miss. DVD-R traded hard to track frequency changes for hard to read wobble-encoded data.

On a DVD+R, however, they came up with a much better method. Instead of changing the frequency of the wobble, or causing amplitude spikes in the wobble, they use complete phase changes. Where CD-R's and DVD-R's methods make you choose between either easy wobble tracking or easy ATIP reading, DVD+R's method makes it very easy to track the wobble, and also very easy to encode data into the wobble. DVD+R's method is called ADIP (ADdress In Pre-groove), which uses a phase change method.

With ADIPs' phase changes, the direction of the wobble changes and continues on going in the exact opposite direction (ie, counter-clockwise to clockwise, or the reverse). For example, if the wobble was 'going up', the phase change causes it to instantly reverse direction start 'going down' no matter where it in the wobble cycle. The phase change is very easy to detect, and also continues for a set period (in this case, one 32T section of the track, or 32 times longer than the pre-pit method of DVD-R).

The state of the phase change (clockwise or counter-clockwise) encodes the individual bits in each block In essence, with the phase change method, not only do you have an easy way of tracking the wobble, but you now have an easy way of reading wobble-encoded data.

As I mentioned earlier, this wobble-encoded data includes error correction of wobble-en

Re:The Matrix

[elrous0]

Actually, IIRC, the worst offender back in the early days of DVD was Polygram. Not only did their packaging suck, but quite a few of their titles (most notably "Kalifornia") simply wouldn't play on Toshiba DVD players or clones (because the Toshibas were strict about not playing improperly mastered discs).

Incidentally, for those who are interested, you can find a pretty good list of problematic early DVD's here.