Wally: glitches

[Brian Ellis]

Wally

I have just completed a 50 min VCD. When playing it back on a stand-alone DVD player, I noticed som e minor glitches over a second or so, in the middle, where the image stopped for a fraction of a second, not at a transition or join, then became blocky for a short fraction of a second and started playing again. I checked the original MPG file at that point and found nothing wrong, nor was there anything to explain it in the MSP set-up.

I then burnt another, identical, disk and it had no glitches. I'm wondering now whether the glitches you experienced in DVDs, as well as these ones, may not have been due to micro-defects in the blank media. It's the first time I've seen an unexplained glitch in a number of VCDs/SVCDs/XSVCDs that I've burnt in the past months.

[wkulecz]

I've concluded such is not the case because:
1) some players do play the disks glitch free
2) The glitches tend to be in the same place on the same player but in different places on different players, even if nominally the same make and model (I've seen this with JVC and Sharp, the only two brands for which I've had access to dupicate models)


Most glitches appear "permanent" on a given player -- meaning that I can rewind (assuming FF/REV works!) and replay that section and see the same glitch. Removing and re-inserting the disk in the same player generally shows the same glitches in the same spot thus it does act like a "bad spot" on the disk. But this spot is not bad on other players, a differnent spot is. And the glitches are gone on certain players.

--wally.

[Sciascia]

Just wondering that since different players use different lasers and thus act differently towards different media could it be a spot or spots on the disc that are "borderline" within tolerance. I mean there are differences between manufacturers for the same medium (in this case CD).

Maybe the physical portion of the drive (in this case laser pickup being the variable) is the culprit. Even if it is the same drive model I would think there are physical differences albeit very minute ones. There is definitely differences between manufacturers, or else the same brands of media would play on all machines, which we all know is not the case. Kind of like a tape based machine.

Possibility?

[Brian Ellis]

Sciascia

I think you may have hit on it. A combined tolerance error of medium and drive. That would explain all the phenomena reported. After all, if you consider the data density on a CD or, even more so, a DVD disk and the precision that that laser beam has to track the disk, it is easily seen it would not require much to upset the applecart. If I remember correctly, the original CD (sound) specification had built-in redundancy which effectively overcame glitches. A question, does such redundancy exist in video standards? I suggest, in my ignorance, that this may not be the case in order to pack in the much higher bandwidth that is required.

[wkulecz]

DVD players should be using 635 nm lasers for "normal DVD".

DVD-R uses 650 nm lasers. This is probably the the cause, and why I have little hope for a real fix in firmware or authoring software. I'd love to be wrong.

Looks like nothing but headaches with DVD-R DVD-RW and DVD+RW for anyone who already has a DVD player, so DVD-burning as a VHS replacement looks much farther away than I had hoped :-(

If you and your audience is willing to buy a new player to watch your disks -- go for it! I was very happy with the quality I got from MSP6.5 or DVD Movie Factory on the players that were glitch free.

--wally.

[Sciascia]

I would have to agree the difference in laser lenght is a physical characteristic and can't be changed with a firmware upgrade. Its a real shame that they couldn't have gotten their act together on the standards in the beginnning.

Do you think that the difference may have something to do with copyright protection? It would make a little sense. If you put a consumer priced burner out there and with the CSS already hacked it would be quite easy to go hog wild on the black market. The movie/production industry may have had a hand in it. I mean illegal SW is so out of hand, if you think it is bad in the states, you should go to Turkey, Kuwait or any Eastern European country. I don't think that I have ever seen a place that sells legal SW in any of those places. Imagine if they got their hands on a DVD burner for a few hundred bucks that could do exact copies. I bought a copy of X-Men on VCD before it was in most theaters. Of course the quality was poor and they didn't charge but a few bucks for it.

Imagine a true DVD copy and it could get completely out of hand. The loss in revenue would either drive production houses out of business (not likely), force them to change encoding or formats (possibly), or charge more money for DVD's (more likely). This would effect DVD sales and it woud drive the same people producing the burners into financial distress. So making an incomaptible drive amy not have been a bad move from a marketing stand point.

[Brian Ellis]

Wally

I don't believe that 15 nm difference in wavelength is going to make a significant change. That is 15 x 10^-9 m = 0.000000015 m, compared to data bits about 60 times bigger. The wavelength difference is only 2.3% and I'm sure there are other tolerances much greater than that. Much more significant is the reflectivity of the sensitive layer in its burnt and unburnt state and I suspect that the 650 nm was chosen because of a spectral absorbivity peak, essential for burning, but less critical for reading. Also essential factors are the track, the consistency of the reflective coating and the homogeneity and planarity (including the coplanarity) of the polycarbonate disk.

Also, if it were a wavelength difference, it would be constant on all players. I think that variations in the thickness of the substrate combined with the mechanical tolerances in the tracking of the players are a much more likely possibility.

I cannot believe that copy protection could possibly play a role here, Sciascia. This, and region protection (God rot the guts of the guy who thought that one up!), are built into the firmware of the player, acting from a code on the innermost track. As you know, it is fairly easy to hack a way round them. There will always be a way to pirate copyright material. Strangely, DVDs seem, as far as I'm able to judge, to be about the only medium where pirated copies are not for sale in this country. It is estimated that >85% of the software used is pirated. I have found pirated CDs, made in China, but the DVDs all seem to be originals, up to now, at least.

[Sciascia]

Another way to keep movies from being pirated is if the media costs more blank than the product you are trying to copy or atleast not cost effective.

new DVD movie off the shelf -- $19.95
Blank DVD disc -- $10-$15?

New program -- $30- $2000
blank CD -- $.20-$.30

That is a hell of a profit margin on the SW side. Then you get into the time to burn a CD vs. DVD. Most people don't really care about packaging for thier SW, it goes in the trash in my house. But I better get a decent case for my DVD, because I will be using that for storage.

As for your other comments Brian, my head hurts now.

[Brian Ellis]

Sciascia

As an ex-programmer, I can't say that the profit margins on specialist software (say, the $2,000 ones) is high. I spent 4 man-years developing a proggy which sold about 200 copies. If you take my salary and overheads as a modest $50k/year, that means my cost price for development alone was $1,000. On top of that, there is the manual which cost about $150 per time, expected support costs and so on. Having the CD-ROMs made (silverware, not ad hoc CD-R burning) cost only $15 each for that time and quantity. We actually sold them for the equivalent of about $2,300 and I think that this was relatively modest, giving us a net profit of about $180, after taxes etc.

I agree that software for public distribution, where sales are in the millions, are a different kettle of fish and are grossly overpriced (hence the fortune of a certain Gates, and others). I'm pretty sure that the actual ex-factory cost of the Office suite, amortisation of development (?) costs included, cannot be more than $20 or 30, so the profit margin is in keeping with the publisher's reputation.

[Sciascia]

Brian

Actually I wasn't talking about legal SW companies profit margin, I was referring to the illegal SW vendor. If he sells a $.30 disc for $15-$30, that is quite a markup. His research and development teams cost are pretty low as well.

If that same illegal vendor was to try to distribute DVDs at $20 a pop, that is a possible $5 profit margin and most people are going to buy the real thing for the same price. Not to mention that the amont of work/time neeed to produce illegal DVDs is much more intense than making an illegal copy of photoshop or something.

[wkulecz]

In laser wavelenght, a little can make a lot of difference since the spot size on the disks are about at the diffraction limit.

I hope this is not a fatal design flaw and DVD-R compatability with the mass of players already out there can be had with updated firmware and/or authoring software. If the playback glitching can be fixed DVD-R is a winner as if all that played didn't glitch claims of ~90% compatability would be true. But I'm afraid they may be ignoring playback glitches in claiming "compatible".

I just know compatability was poor back in October so I returned my burners. Pioneer has had two firmware updates since then. That's why I want to know how it goes for you.

--wally.

[Michel Carleer]

A small change in laser wavelength can make a huge difference in spot size indeed, but probably not because of the wavelength change.
Another possible cause is that the lasing medium is different and as a result the optical properties of the output beam can be very different (collimation and spot geometry).
Michka

[zeb7]

wkulecz ,
"1) some players do play the disks glitch free
2) The glitches tend to be in the same place on the same player but in different places on different players, even if nominally the
same make and model (I've seen this with JVC and Sharp, the only two brands for which I've had access to duplicate models) "


Well i've had my share of CDRW incompatible , i have two L.G. drive's both can record to Traxdata CDR's
but only one is able to read from the Traxdata CD's ?
my point being that i don't get read errors from the CD's ( its all or nothing )

I have seen the things Wally described in earlier post (stuttering,freezing,cutingout ) and the re-syncing error Brian
described above . i believe their are two likely courses

1 Read error ( Brian successfully burned a second disc with no error's / I don't think Wally ever did ? )
2 Decoder buffer underrun/overrun due to improper Multiplexing ( good DVD player attempt's re-syncing )

My Question is Wally did you try copying a retal/real DVD ? with permission i'm sure :-)
this would of eliminated all authoring errors

[wkulecz]

No I never tried copying a DVD, since they are designed not to be copied it would introduce more unknowns making it hard to see what I'd learn from it. You weren't the first to suggest this. Someone back in October suggested I should get an "adult DVD since most of these aren't CSS". I've no idea if this is true or not and no inclination to find out. I've nothing against adult DVDs other than I find them boring, since my wife's great, I got the real thing!

At $5-10 a pop for DVD-R back in October, I never tried duplicate burns. But all my disks seemed to play glitch free on the Pioneer DV-343, and all glitched on most other players.

Its not clear to me that new CD-R features like "burnproof" will screw up VCD or not if they kickin. I've not played much with VCD or SVCD but I tend to use "slow" 4X CD-RW media so burnproof shouldn't kick in. I find compatability of these in stand-alone players far too iffy to useful, but since they are so cheap to do this is not a major problem if you want to try.

--wally.

[zeb7]

just to be sure my post dose not seem ungrateful its worth saying, Thanks wally for all the feedback you gave us on
DVD-R , i had high hopes of problem free operation ,you have probably saved me money/time.
--------------
I wasn't referring to the IDE bus > CDWR buffer (burnproof) , But to the buffers within the Mpeg decoder (software/hardware)
because audio and video packed in chunks and if the chunks are to big , the data will not stream smoothy
from the CD/DVD.