Weird issue with DVD-video ISO and ODD emulators

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tomman

Posted on 18-11-22, 01:04

Dinosaur

Post: #40 of 1315
Since: 10-30-18

Last post: 58 days
Last view: 18 hours

Usually when I download a DVD ISO rip of whatever stuff I can find, all I have to do is to mount it using my optical disc drive emulator of choice (WinCDEmu under Windows, CDEmu under Linux), and let media players pretend they're dealing with an actual physical disc made of ol' fashioned polycarbonate. As long as whoever did the rip wasn't drunk/high and didn't screwed up in the basics (removing CSS crypto, testing their uploads to ensure there were no flipped bits in the way), I've never had problems with this. The worst I've had to deal so far were with proprietary file formats (because LOLJAPAN and fuck you very much China), and even those are usually not a problem for CDEmu (mount the image, properly "re-rip" it to standard formats, done).

BUT! There is always a first time for everything!

See, one of the many things I'm trying to collect are Touhou video releases on CD/DVD/BD, mostly becaue ~~I will never play the games~~ you can always find some cool shit which are nice to have on something that isn't a 4th-generation hardsubbed YouTube reencode (and here is where the "preservation" aspect kicks in: my collection right now is tipping the scales at ~290GiB, mainly with help of random guys around the Internets -none of them from behind the Great Firewall of Chinese Hoarders, thankfully-... and yes, I HAVE BACKUPS OF MY BACKUPS!). Since this is... well, Touhou, it means we're dealing exclusively with doujin productions, which are a PITA on itself to source (things have been a nightmare since Japanese rippers vanished from the scene and Chinese file hoarders seized it for the good of nobody). Long short story: someone uploaded this rip of some release by Yuuhei Satellite. The rip is in standard ISO, but Weird Things Happen when I mount said ISO with my ODD emulators and try to play the DVD: $OS will mount the filesystem, $MEDIAPLAYER will recognize there is a proper DVD-Video structure and attempt to play the disc... just to get a black screen where a menu is supposed to be (or nothing in the case of VLC). When I manually specify a track/chapter, I still get a black screen... and heavily distorted audio. Tested with mpv, Xine, several versions of VLC, MPC-HC, and even WMP, so it isn't media player or even OS-specific. Tried also manually opening the main VOB (VTS_01_1.VOB) with same results: no video, distorted audio.

But here is the kicker: turns out that VLC CAN play DVD media from raw ISO files, no need to mount them. And sure enough, if I just open the ISO with VLC, the fucker DOES PROPERLY PLAY! The menu works, all chapters do play spotlessly, audio is completely clean and beautiful, etc! So... what in the name of Tanned Cirno is happening here!?!?!??!

Anyone can test this: there is a download link for the ISO on that forum thread I've linked to (amazingly the link is still alive, despite being Mediafire). Mount it with your ODD emulator/virtual drive software of choice and watch it how your favorite media player chokes with it. But if your media player can access ISO files, it should play OK... I should try burning this to a DVD and checking if it still fails there.

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KoiMaxx

Posted on 18-11-22, 07:01 (revision 1)

Post: #22 of 159
Since: 10-29-18

Last post: 206 days
Last view: 1 day

I can confirm it happens regardless of ODD emulator I used (Win10 native, WinCDEmu) and player (MPC-HC). After mucking around on the interwebz I found this excerpt from a thread on reddit:

Is libdvdcss legal? The use and distribution of the libdvdcss library is controversial in a few countries such as the United States because of a law called the DMCA (Digital Millennium Copyright Act). If you are unsure about the legality of using and distributing this library in your country, please consult your lawyer.

Note Beware: VLC media player binaries are distributed with the libdvdcss library included.

I think that ISO wasn't unscrambled at all. Knowing that, it would make sense that it would only work on VLC.

I still have no idea what I'm talking about.

tomman

Posted on 18-11-22, 12:06 (revision 3)

Dinosaur

Post: #41 of 1315
Since: 10-30-18

Last post: 58 days
Last view: 18 hours

...you've hit the nail in the head!

Wow, first time I see a doujin DVD with CSS protection. Aren't you supposed to pay extra for that?

And indeed, enabling CSS/CPPM support on CDEmu does allow libdvdcss-enabled players to properly play the disc (just tested with Xine). I guess I'll now need to find a way to make a descrambled version of this ISO, because I can't archive this as-is. This explains why VLC could play the scrambled ISO just fine - it walked the extra mile and pretended to be a DVD drive too, complete with the DRM bits. Awesome, although impractical for my purposes. Also, CDEmu is awesome too~

A pox over Yuuhei Satellite for letting their DVD duplication service infest their discs, and a bigger one over whoever ripped this ISO without taking care of descrambling the disc.

UPDATE: This took care of the descrambling bits - it requires libdvdcss and works with both ISO images and real/fake drives, outputting a clean, descrambled ISO that works properly everywhere.

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Kakashi	Posted on 18-11-22, 16:06 Hi.
Post: #38 of 210 Since: 10-29-18 Last post: 1876 days Last view: 1848 days	UPDATE: There's way to hit a nail inside it's head with a hammer!

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