Chris123 Posted August 23, 2008 Posted August 23, 2008 Hi, I burned a DVD video from files using ImgBurn 2.4.1, and for some reason the MD5 hash of the identicle files VIDEO_TS.BUP and VIDEO_TS.IFO has changed even though their size remained the same (the rest of the files weren't changed at all). I wasn't prompted or notified about this by the program. I tried to burn the same files with Nero 7.5.9, and it DIDN'T change the hashes, but it did give these warnings: When I used with Nero the files altered by ImgBurn, it gave different errors: The warning about VIDEO_TS.VOB is now replaced with a more generic error. I tried to burn another DVD video with both programs, and NOTHING was changed (nor were any errors given by Nero). Both DVDs seem to work fine in a standard DVD player. I'm a little bit puzzled by this since I don't know what the VIDEO_TS.BUP/VIDEO_TS.IFO files contain, and ImgBurn didn't notify me about anything. Anyone has any ideas? Thanks P.S. I attached the original and altered VIDEO_TS.BUP, as well as the VIDEO_TS.VOB that Nero complains about. files.zip
Cynthia Posted August 23, 2008 Posted August 23, 2008 Nero does a check that the associated vob files are there and also that there are no additional ones that is not referenced in the VIDEO_TS.IFO file. That's why you get the 'reallocation error' in Nero. ImgBurn only does a 'Get VTS sectors' and only fails if here is a .ifo/.bup file missing and not if there are missing .vob files or additional ones, as in your example. On some DVDs there are dummy/fake menu vobs like in this case, the VIDEO_TS.VOB. The reason might be to get the bup and ifo version of the VIDEO_TS to be placed in different sectors opposite of each other on the disc surface to avoid a scratch on the disc that makes it impossible to read both of them. If you get a scratch on one side of the disc - the other side should be fine and the other VIDEO_TS file can then be read by your reader/player and the disc is then not totally useless. Some movie studios also put a huge fake menu vob file on the disc to make it harder to get a decent compression out of the DVD. In this case, the VIDEO_TS.VOB file can be deleted without issues. ImgBurn uses the 32K padding option to avoid this 'scratch' scenario. From the guide section: IFO/BUP 32K Padding There can be gaps on a DVD. The most notable ones are those used to ensure that no ECC block contains any portion of an IFO file and its associated BUP file. Often times, you will see commercial DVD's authored with tiny menu files of 40 or 50 kb, exactly for this purpose. Since ECC blocks are 16 sectors long (32K), the easiest way to accomplish this is to ensure that there are 16 sectors between the end of the IFO and the start of the BUP. With VIDEO_TS.VOB or VTS_xx_0.VOB files less that 32K (or absent) this means using a gap. If an IFO is unreadable (e.g. a CRC error in a sector), the player looks for the BUP, which is stored on the disk right after the VOBs for the title set. Now suppose the VOB's for that title set are small and the data is packed in. There is a chance that the BUP occupies exactly the same bad block that the IFO did, making the BUP useless and the disk, dead in the water. Essentially, the basic problem is that without the proper spacing, a single CRC error that would normally only affect one of the two files will affect both, rendering both useless. If proper spacing exists, it would take at least two CRC errors (one affecting each) to render both the IFO and BUP useless.
Chris123 Posted August 24, 2008 Author Posted August 24, 2008 Thanks for the explanation. However, I don't think it's the reason for the hash change - first, because from what I understand the padding takes care of the PHYSICAL place of these two files on the disc surface, so it shouldn't touch their content, and second, because I unchecked the padding option (under Build tab) and the hash was changed in exactly the same manner... it's very unusual for a burning program, especially such an accurate one such as ImgBurn, to change file contents... By the way, when burned from an image, the files hashes DO NOT change, but I guess that's obvious.
LIGHTNING UK! Posted August 24, 2008 Posted August 24, 2008 It changes them to correct things that are wrong... and that's only ever going to be the various offsets that are fixed by a quick 'fix/get vts sectors' type function (from the ifoedit days). It's not hard to compare the modified files against the originals and see exactly what's changed. Do that and you'll have your answers.
blutach Posted August 24, 2008 Posted August 24, 2008 If padding is applied (32k sectors on), then the various sector references in the VMG_PTT_SRPT and VTS_MAT tables are altered. This is how the DVD actually reads the disc - by examining these sector references. Oh, and even if you haven't used padding, the files can be moved if you are doing a DL disc, where the LB cell needs to end on a sector that is a multiple of 16. Just the rules of DL burning. I burned a DVD video from files using ImgBurn 2.4.1 Please upgrade to the latest version - it's free. Regards
Chris123 Posted August 25, 2008 Author Posted August 25, 2008 It changes them to correct things that are wrong... and that's only ever going to be the various offsets that are fixed by a quick 'fix/get vts sectors' type function (from the ifoedit days). It's not hard to compare the modified files against the originals and see exactly what's changed. Do that and you'll have your answers. Thanks. I don't know too much about these offsets or ifoedit days (yet), but comparing the files sounds promising. I actually tried that already, but the only tool I could think about is notepad, which didn't help of course what should I use to compare them? If padding is applied (32k sectors on), then the various sector references in the VMG_PTT_SRPT and VTS_MAT tables are altered. This is how the DVD actually reads the disc - by examining these sector references. Oh, and even if you haven't used padding, the files can be moved if you are doing a DL disc, where the LB cell needs to end on a sector that is a multiple of 16. Just the rules of DL burning. Well, it's not DL and I disabled padding to test this, and the files were still changed. I burned a DVD video from files using ImgBurn 2.4.1 Please upgrade to the latest version - it's free. I just did, thanks
LIGHTNING UK! Posted August 25, 2008 Posted August 25, 2008 I normally use 'hex workshop' but something like 'Beyond Compare' with the hex viewer plugin would work just fine too. When you know which bytes have been changed (and their offset from the start of the file - probably going to be in the first 2048 bytes of the file), open said IFO/BUP file in IfoEdit and see which field is at that location.
Chris123 Posted August 28, 2008 Author Posted August 28, 2008 Thanks for all the advice. Since the DVD works, I think I'll just leave it at that. I do think though that ImgBurn should let a user know when it changes files, and why... By the way, I know it's offtopic, but is there an easy way to rip subtitles off of a DVD? Single-language SUB/SRT would be best, but multilanguage IDX+SUB is also fine.
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