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Skipping with remote Syabas server

 
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garyfritz



Joined: 08 Apr 2006
Posts: 10596
Location: Fort Collins, CO


PostLink    Posted: Tue Jan 15, 2008 4:32 pm    Post subject: Skipping with remote Syabas server Reply with quote


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This is an odd problem and I don't really expect anybody to solve it, but maybe some of you HTPC experts have some insights...

I use a Momitsu v880N DVD player. While not a "real" HTPC, it is in fact a diskless Linux-based HTPC in a commercial box. It's also network-capable; it can play VOB files on a remote server using, apparently, a Syabas protocol. The Momitsu server runs on my PC a few rooms away from the HT.

I've been using it for years with very few problems. I have occasionally seen "jumps" in VOB files, where the movie skips a few seconds and the audio drops out, but it's fairly rare. It generally happens at scene changes, for some reason.

I just ripped a copy of Meet the Robinsons and watched it with my kids, but the movie was full of skips and audio dropouts. They didn't happen at scene changes like I'd seen before. I dug into it a bit and it got more mystifying:

* I can play the VOB file locally on my PC, using PowerDVD, and there are no skips.
* I tried setting the priority of the server process higher -- no change.
* The movie skips in the SAME PLACES every time you play it.
* I tried copying the file, in case there was something wrong with some spots on the disk. The copy also skipped in the same places.
* I tried defragging the disk. No change.

The fact that the movie always skips in the same places, and that it's not apparently connected to the location on the disk, indicates to me that something is wrong with the data in the VOB file itself. But if so, apparently it's something that the Momitsu server is sensitive to but PowerDVD isn't.

I wanted to try playing the movie with a different Syabas server (wizd), but I had only saved the VOB of the movie itself. wizd requires the entire directory tree of the DVD. I'd have to go rent the movie again if I wanted to try that. (Might be interesting to do that anyway, to see if ripping the VOB again produced the same results, but I'm not sure it's worth it.)

Any ideas or suggestions what might be causing this, either in the MtR VOB or in other movies?

Thanks!
Gary
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AnalogRocks
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Joined: 08 Mar 2006
Posts: 25431
Location: Toronto, Ontario, Canada

TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Tue Jan 15, 2008 5:03 pm    Post subject: Reply with quote

The only thing I can think of off the top of my head is the studio's like to put bad 'sectors' (for lack of a proper term) on a lot of the DVD's they release today. It's suposed to stop you backing up the disk. But from what I have read the programmers come out with a fix for it a week later anyways.

Maybe it's time to upgrade your backup software.

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garyfritz



Joined: 08 Apr 2006
Posts: 10596
Location: Fort Collins, CO


PostLink    Posted: Tue Jan 15, 2008 5:56 pm    Post subject: Reply with quote

Don't those copy-protection schemes usually prevent the copies from succeeding at all? And if the "bad sectors" caused the backed-up data to be faulty, wouldn't PowerDVD barf on it too?

Related question: they keep changing the encryption/protection schemes so older ripping tools don't work any more. How do they break those tools, but any old $88 DVD player can still play the disk??
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lyd



Joined: 15 Sep 2007
Posts: 390
Location: Pending: Deerfield, WI


PostLink    Posted: Sun Jan 20, 2008 1:32 am    Post subject: Reply with quote

garyfritz wrote:
Related question: they keep changing the encryption/protection schemes so older ripping tools don't work any more. How do they break those tools, but any old $88 DVD player can still play the disk??

You might find this little write-up interesting, with respect to that question.

lyd

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AnalogRocks
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Location: Toronto, Ontario, Canada

TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Sun Jan 20, 2008 10:03 am    Post subject: Reply with quote

lyd wrote:
garyfritz wrote:
Related question: they keep changing the encryption/protection schemes so older ripping tools don't work any more. How do they break those tools, but any old $88 DVD player can still play the disk??

You might find this little write-up interesting, with respect to that question.

lyd


I have a $35 DVD player that has probelms with lots of disk's. Never on the older titles though. It often hangs and I have to restart the player and chapter forward to the next chaper after the crash and rewind to a point just after the crash. It's such BS.

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AnalogRocks
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TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Sun Jan 20, 2008 10:03 am    Post subject: Reply with quote

Hey lyd. Did you by chance save that article. The page is gone.
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lyd



Joined: 15 Sep 2007
Posts: 390
Location: Pending: Deerfield, WI


PostLink    Posted: Sun Jan 20, 2008 11:06 am    Post subject: Reply with quote

AnalogRocks wrote:
Hey lyd. Did you by chance save that article. The page is gone.
Try again? It loads fine for me. Here's most of it, though.


A history of DVD copy protection

While I was out, I wrote many things. I’m still trying to find them all, truth be told, to cobble them together and weave them into some sort of Magnus Opus Lifework. I’ll let you know how that works out. In the meantime, here’s a history of DVD copy protection that I posted on Dave Shea’s blog in response to his first conscious encounter with DVD copy protection. Parts of this may be wildly inaccurate; other parts may be laughably incomplete. I make no claims either way.

In the beginning (of DVDs) there was CSS — the Content Scramble System, not Cascading Style Sheets Wink — which was famously cracked many years ago by “DVD Jon”. CSS is technically optional (for example, Jason Scott’s excellent BBS Documentary doesn’t use it) but virtually every commercial DVD uses it.


It is possible that the warning you [Dave] saw referred to CSS protection and nothing more.


Some reference material:



Also since the beginning, DVDs have had the option of embedding a region code in the DVD disc. Different regions of the world were assigned different codes, and every DVD player manufacturer had to sign an agreement with the DVD Consortium stating that they would only play DVD discs of a certain region. And the manufacturers had to play by the Consortium’s rules, because the Consortium was the only one who could give out the decryption keys that would allow the player to decrypt the CSS encryption used on commercial DVDs.


Despite these agreements, in some regions of the world (i.e. everywhere but the United States), there was a growing market for “multi-region” DVD players which would play DVDs from anywhere, i.e. a DVD player in the UK (region 2) which could play DVDs from the US (region 1). (Many were region-locked by default but had secret codes that could enable the extra functionality.) To counteract this trend, Columbia Tristar and Warner Home Video attempted a new scheme called “region code enhancement” (RCE). An RCE-protected DVD disc contains executable code that asks the DVD player what regions it supports, and refuses to play the disc if it didn’t like the answer. All DVDs can contain executable code which is executed by the DVD player – that’s how menus and other features work. But this code tried to outwit the “multi-region” DVD players in order to enforce in software the region encoding scheme that the players refused to support in hardware. There were various improvements to RCE over the years, as multi-region players adapted to older techniques.


It is possible that the warning you saw referred to RCE protection. “Multi-region” DVD players – even ones made by legitimate mainstream manufacturers – have been called “unlicensed” or “unapproved” devices by studios still trying to divide the global permeable marketplace into regions with impermeable boundaries and sharp corners.



Eventually the multi-region DVD players got so smart that they were software-indistinguishable from region-locked players, and the studios gave up and focused on a new threat: DVD ripping programs. As I mentioned earlier, DVDs contain executable code that tells the player what to do next – go to this menu, set this register, jump to this track or chapter, etc. That means that in the normal course of playing a DVD, there could be tracks (or individual chapters within a track) that you would never reach. Even if you tried to reach them (by using navigation buttons for “next track” or “next chapter” or whatever), those are really just commands to the DVD player and they can be overridden by code on the DVD disc that tells the DVD player to do something else. So the disc could have a bogus track or a damaged sector, and on a regular (*cough* “approved” *cough*) DVD player you would never even notice.


But DVD ripping programs don’t execute code; they blindly read every byte off the disc and decrypt it. So Sony introduced ARccOS protection, which involved placing intentionally bad sectors in parts of the DVD disc and then programming the disc to never go there during the normal course of playing it. Of course, DVD ripping programs were quickly updated to read the DVD directory structure to determine which tracks and sectors were never actually used, and if they found a bad sector in one of those tracks they simply skipped over it without complaining.


It is possible that the warning you saw referred to ARccOS protection. Sony licenses it to various other studios, and reports of its death have been greatly exaggerated. (“Pirates of the Caribbean: Dead Man’s Chest” is reported to use it, and it just came out on DVD last month.)




In 2005, Macrovision introduced yet another protection scheme called RipGuard. I have not been able to find a whole lot of technical details about how it works, except that they essentially reverse-engineered several DVD ripping programs and created a protection scheme that exploited as-yet-unknown bugs in those programs. They also claim to be able to “update” the protection for new discs as bugs are fixed in the ripper programs. (Later in 2005, Macrovision actually bought the IP for DVD Decrypter, which was at the time the most popular program for Windows, and updated RipGuard so DVD Decrypter wouldn’t work.) So basically, “RipGuard” is just a generic catch-all term for “here’s all the ways we’ve found to f*ck with you so far, but be sure to ask again tomorrow.”


It is possible that the warning you saw referred to RipGuard protection.




As you correctly pointed out, without buying the discs and opening the package, there is no way to be sure which protection scheme (or combination of protection schemes!) are present, and therefore whether the discs would work in your gift recipient’s DVD player.


Ironically, every modern DVD ripping program can easily auto-detect and auto-bypass all of these protection schemes, and then re-author the disc onto ultra-cheap recordable media with no protection whatsoever. If you wanted to ensure a smooth Christmas morning (and didn’t mind breaking several federal laws), you should buy the discs and re-author them unprotected, and keep the originals in a drawer. As I said in my first blog post ever, “the only long-term effect of copy protection is to ensure that those who defeat it are immortalized.”


By the way, the title of that first-blog-post-ever was “My crush on Spyro, what Flash animations remind me of, and what the past will look like someday.” Someday is closer than you think.


Shortly after writing all of this on Dave’s blog, it was pointed out to me in private email that the copy protection notice could simply refer to the original Macrovision protection, which has been around since VHS days and was designed to prevent DVDs from being copied across analog cables (e.g. to VHS tapes). So that’s #5 on the list of possible explanations for the “copy protected” warning on DVD labels. (And like the others, Macrovision can be used in combination with other forms of copy protection.) It should also be noted that Macrovision protection has never been particularly effective — even in the analog world before DVDs and DVD rippers — despite the overwhelming business advantage of being mandated by federal law.

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