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Old 20th May 2006, 22:33   #61  |  Link
windtrader
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done some research

I've been doing a fair amount of research into this somewhat esoteric topic and found the most relevant technical information in a document titled "ECMA Technical Report /TR71 dated February 1998. It is very detailed and has data field descriptions and specifications to the BIT level. I also went down the mkisofs hole but it dead-ended since I could not find any information about how it internally handles reading the DVD disc. There are DVD disc reading procedures in the previous document.

TR/71 section - ECMA-119 Directory Structure ad Path Table 3.7
This section shows the DVD physical file structure. Annex B describes the logic to read the DVD. It appears there are only three specific sector addresses where data is expected:
Primary Volume Descriptor, logical sector numbers 0-15,
Volume Recognition at sector 16 and
Anchor point at sector 256.

Everything beyond appears as vector based structures (FIB and ICB seems to be the key vector tables to the actual file data) so it might be possible to physically layout the files in any order as I did not see a specific reference stating the files must be written in a certain order. However, all examples (UDF FIle Structure - ref table 21, figure 7) show the following order:

VIDEO_TS.IFO VIDEO_TS.VOB VIDEO_TS.BUP VIDEO_TS_01_0.IFO VIDEO_TS_01_0.VOB VIDEO_TS_01_0.BUP
etc. etc. etc.

I'm sure with all the various DVD formats it's possible some DVD Player software make certain assumptions / interpretations that cause the player to fail to read some of the formats like this one.

Having a better apprecation for all the CRITICAL control data stacked at the front of the disc, it is also fairly obvious to me the condition of media that gets a nick in this area - *COASTER*.

As stated in other replies, the menu VOB of a DVD provides the IFO and BUP physical separation. The larger it is, the better chance the player is able to use one of them to keep navigating the disc. But many backed up discs are strpped of their menu, resulting in the IFO and BUP being physically adjacent and if one is bad, so is the other. Thus the rational behind the 32k fix.

So, how much physical separation is there really in a 32k gap? I'd argue that it is so small it basically provides no practical improvment in integrity of the VMG structure. I'm no physicist but it must be so small it is not visible to the naked eye, especially being at the inner ring . Maybe making the buffer large enough to create some reasonable physical separation would make this fix work on a practical level.

I did not come across any reference to any back up strategy for the first three critical DVD data structures; thus, I'd argue the whole concept of BUP backups of the VMG are of no practical value. With unreadable area at the front of the disc, it seems practically the chance of any of the disc being readable and useable is very low. However, I can see the potential benefit that the main movie vobs ifos and and bups would help the player keep going if encountering a bad IFO or BUP.

I did not write this to devalue any of the good work or intentions of the 32k patch since I know the spirit of it is to better the world for us DVD backupers. I'm just stating my analysis leads me to an opinion that the amount of real world, practical improvement of this specific patch is nonmeasureable or at least very unlikely to be actually useful.
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Old 21st May 2006, 03:11   #62  |  Link
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I have some sympathy for what you are saying windtrader. Oftentimes we find an unplayed menu file of 358k and others of 38k (weird sizes), including a (sometimes) unreferenced VIDEO_TS.VOB of these sizes - all designed to give maximum chance of at least one of an IFO or a BUP being able to be read.

But, no doubt, a badly damaged DVD will have troubles irrespective of gaps - we've all had problems with these.

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Old 21st May 2006, 09:40   #63  |  Link
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I agree.

Perhaps I could modify the 32K gap method to use a larger gap whenever possible. But I don't want to push the real data too far to the outer edge, because this part of the DVD is more subject to defects and damage.
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Old 21st May 2006, 17:18   #64  |  Link
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maybe give the user a choice to how much they want to seperate them?
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Old 22nd May 2006, 02:59   #65  |  Link
windtrader
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Magic number

I did some more thinking about how large a buffer should be placed between the VIDEO_TS.IFO and it's BUP if there is no menu VOB.

The sizes we deal with DVD is really amazingly minute and it is a wonder any of this works at all. As you know the binary on/off is implemented by "burning pits" into the media. The track pitch (width) is 74 microns; 1,351 fit in one mm. A tiny visible spec/defect would span many tracks. The placement of the main IFO/BUP is separated by the main VOB. Since there are only a handful of these VOBs there is quite a physical distance between them and it is easy to understand how effective this can be.

The problem with the VIDEO_TS IFO and BUP is that you really can't create a big enough buffer to be effective, like the main vobs. Since you won't make a large buffer that would create the physical separation along track pitch, another option would be to try to place the IFO and the BUP 180 degrees away from each other; in other words, place them directly across the disc from each other.

I did some calculations, that are not exact, but pretty close, as I cross referenced them to a few sources and they seemed to be in the ballbark. Based on these calcs, I determined that the target buffer size should be about 29,158 bytes.

Note: I found a late reference that states the location of the lead-in is at 45mm. I based my calcs on 48mm, so the size may be a little smaller, closer to 27,070 bytes.

Kind of funny after doing all that work, it is pretty damn close to the 32k that is used but based on an entirely different rationale.

cheers!


DVD (120mm) Capacity
total bytes 4,700,000,000
Mbytes 4,700
Mbits 37,600
max read rate (mbits/sec) 10.8
max read rate (mbytes/sec 1.35
seconds of stream 3,481
minutes of stream 58

rev/
recording location limit(mm) circum(mm) RPM sec
outer 116 364 1,389 9.57
middle 82 258
inner 48 151 574 23.15

recording width - mm 34
microns per mm 1,000
track pitch - micron 0.74
track density / mm 1,351
total tracks 45,946

travel (mm) / sec 3,491
bits /mm @10.8mbs 3,094
bytes/mm 387
semi-circle dist @ inner 75
bytes in 1/2 circ.@ inner 29,158

* lead in is at 45mm, lead-out at 117mm
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Old 22nd May 2006, 10:07   #66  |  Link
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OK, so the actual 32K gap is just fine! Therefore, I will not change the current method.

However, note that the gap before VIDEO_TS.BUP is increased (sometimes by a very large amount of sectors) when a DL-DVD is used. It's needed to align the LB cell properly, and to put at least the same amount of data on L0 than on L1. In this case, of course, I can't choose the size of the gap freely.

Thanks for your investigations!
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Old 22nd May 2006, 10:39   #67  |  Link
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Quote:
Originally posted by mpucoder:
So ensuring 32k between ifo and bup is the simplest solution to ensure they are in different ECC blocks.
Yes! That's it, no more.
Quote:
Originally posted by rOlZ:
OK, so the actual 32K gap is just fine! Therefore, I will not change the current method.
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Old 21st November 2006, 12:33   #68  |  Link
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I have a problem of burning with PgcEdit.
Recently I tried to burn dl disc and I decided to follow the guide and I did succeeded burning a dl disc after failing one time.
Now this time I tried to burn another one. After loading the movie (6.1G), I checked the 32k gap option I press the burn logo, it asked me to save the project and then did not do anything else. Then I checked the burn DVD setup, everything seemed ok but still there was no action. Then I brought up the ImgBurn to check the disc and when I press save, at times an error message would show as follows:

invalid command name ".burn.opts.burn"
invalid command name ".burn.opts.burn"
while executing
"$w.opts.burn configure -state normal"
(procedure "validate_burn" line 18)
invoked from within
"validate_burn"
(procedure "::burn::setup" line 248)
invoked from within
"::burn::setup ."
(menu invoke)

and afterwards that the program will stop to function and stopped there after the error, refusing to return to the main program.

So, what could probably wrong? I had reinstalled ImgBurn and even installed another window but with no luck. I had also tried two versions of mkisof.exe.
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Old 21st November 2006, 15:16   #69  |  Link
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It's probably a bug in PgcEdit. I'll try to fix it. Thanks for the report.
BTW, are you running Windows XP?

In the meantime, you can burn your DVD-Video files with ImgBurn v2, as it has all the features present in the burn function of PgcEdit. You can even burn your files directly, without having to write the ISO on HDD first. PgcEdit is not necessary any more to burn a DL DVD.
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Old 21st November 2006, 16:10   #70  |  Link
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Thanks for the prompt reply, I'm running XP.
I'll try to burn it with ImgBurn later.
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Old 21st November 2006, 22:58   #71  |  Link
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if an iso image is crated of a dvd using the guide on the first page, does it matter which burning software is used to burn the image? or is imgburn still preferred?
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Old 21st November 2006, 23:15   #72  |  Link
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If it's a DL, you MUST use ImgBurn. For a single layer, you may use whichever program you have, even Ner0 if you really want so.
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Old 12th December 2006, 06:47   #73  |  Link
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After reading through several threads on this topic, I have a few questions. I'll try to separate them out as best I can.

1a. Regarding ImgBurn v2. It was stated above that it has all the burning capabilities of PgcEdit. Does this mean I can burn single layer dvd files directly (without creating an ISO first), and ImgBurn will create the 32K gaps?

1b. If the answer to 1a is no, will ImgBurn v2 create the 32K gaps for me if I create an ISO first? Or is PgcEdit still required to create the 32K gaps, then ImgBurn to burn?

2a. I've been using CloneDVD2+AnyDVD for quite some time now. Does anyone know if CloneDVD2 writes the 32K gaps? This program can be used to write existing DVD files (IFO+BUP+VOB), so this would be useful knowledge.

2b. Is the a way to verify the 32K gaps have been written to a DVD? I know a hex editor can be used to verify this in an ISO, but what about a finished burned DVD?

Thanks for all the info. I swear I learn something new every day around here...

Last edited by wraithdu; 12th December 2006 at 06:59.
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Old 12th December 2006, 07:14   #74  |  Link
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1a. Yes
1b. N/A
2a. Don't think so - could be wrong.
2b. Read the DVD in DVD Decrypter in ISO Read mode. Then use ISOBuster. But ImgBurn certainly does.
3. If you are at all worried about gaps not being written, then use VobBlanker - latest beta to create "smart gaps".
4. Welcome to Doom9!

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Last edited by blutach; 12th December 2006 at 07:17.
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Old 12th December 2006, 10:08   #75  |  Link
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2b. You can also verify the start LBAs of all DVD-Video files with DVD Decrypter. They are reported in the log in debug mode. To enter Debug Mode, press the F6 key. Then, you have to eject and reload the DVD, to force DVDD to update the log.
If the 32K gaps are used, the IFO and BUP must be separated by at least 16 sectors.
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Old 12th December 2006, 22:04   #76  |  Link
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Thanks so much for the quick replies. Being the type of guy that likes to see things for himself, I made some test burns today, and here are the results.

I did a quick re-author in shrink so I had a DVD that would exhibit the problem, ie no video_ts.vob file. I burned the files with ImgBurn v2, Nero 6.6.1.4, and CloneDVD2 2.9.0.1. I then viewed the burned DVDs using DVD Decrypter's debug mode (a very handy feature).

ImgBurn, as stated above, burned correctly, inserting a 16 sector gap in between the video_ts.ifo and .bup. Nero 6 and CloneDVD2 both failed this test. Both of those programs burn the files contiguously.

So there we go. Looks like I'll be switching to ImgBurn for all my burning needs. Thanks again!

Last edited by wraithdu; 12th December 2006 at 22:06.
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Old 13th December 2006, 00:16   #77  |  Link
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Quote:
Originally Posted by wraithdu View Post
ImgBurn, as stated above, burned correctly, inserting a 16 sector gap in between the video_ts.ifo and .bup. Nero 6 and CloneDVD2 both failed this test. Both of those programs burn the files contiguously.
ImgBurn is a very good option. But if you want to "see" the gaps as files (unreferenced menu VOBs) try VobBlanker. Its output can be burned with any prog, even Nero.
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