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DVD FAQ. Часть 4.1


[4.4] Почему вместо скриншота с DVD я получаю фиолетовый или черный прямоугольник?

Большинство компьютеров с приводами DVD, даже если видео воспроизводится с помощью программного декодера, используют видеооверлей для вывода картинки непосредственно в видеосигнал. Этот способ - наиболее эффективен при работе с большими потоками данных полноценного видео. Некоторые системы, такие как, например, декодер Creative Labs Encore Dxr, используют сквозной кабель, который перекрывает аналоговый видеосгнал, поступающий с видеоадаптера. Видеооверлеи используют технологию цветового ключа (colorkey) для выборочной замены пикселов определенного цвета (обычно это фиолетовый или почти черный) декодированным видеосигналом с DVD. Как только DVD-декодер обнаруживает пиксел этого выбранного цвета в видеосигнале, он немедленно заменяет его собственным видеосигналом. Этот процесс проистекает из видеопамяти компьютера, так что если вы попробуете снять скриншот, который забирает цвета пикселов из видеопамяти, вы получите картинку с прямоугольником, цвет которого совпадает с цветовым ключом.

[4.5] Почему нельзя смотреть скопированные на жесткий диск фильмы?

Большинство фильмов закодировано системой защиты от копирования CSS (см. 1.11).  Ключи для дешифрования записываются на недоступную для обычного чтения область диска. При копировании содержимого с защищенного DVD на жесткий диск ключи не копируются. Поэтому, как только вы попытаетесь воспроизвести VOB-файл, декодер запросит ключи и не найдет их. Скорее всего, вы получите сообщение "Cannot play copy protected files".

[4.6] Почему у меня проблемы с воспроизведением DVD на компьютере?

There are thousands of answers to this question, but here are some basic troubleshooting steps to help you track down problems such as jerky playback, pauses, error messages, and so on.

  • Get updated drivers. Driver bugs are the biggest cause of playback problems, ranging from freezes to bogus error messages about regions. Go to the support section on the Web sites of your equipment manufacturers and make sure you have the latest decoder drivers as well as the latest drivers for your graphics adapter and DVD-ROM drive.
    Apple has released numerous updates for audio drivers and the DVD player application. Make sure you have the latest versions. Go to the downloads page and search for DVD. 
  • Make sure DMA is turned on. For Windows, go into the System Properties Device Manager, choose CD-ROM, open the CD/DVD driver properties, choose the Settings tab, and make sure the DMA box is checked. Caution: You may run into problems with an AMD K6 CPU. Check for a BIOS upgrade and a CD/DVD-ROM driver upgrade from your system manufacturer before turning DMA on. 
  • If you get an error about unavailable overlay surface, reduce the display resolution or number of colors (right-click desktop, choose Settings tab).
  • Try turning off programs that are running in the background. (Close or exit applets in the Windows system tray.)
  • If you are using a SCSI DVD-ROM drive, make sure that the it's the first or last device in the SCSI chain. If it's the last device, make sure it's terminated.
  • Bad video when connecting to a TV could be from too long a cable or from interference or a ground loop. See 3.2.2.

More information on specific graphics cards and driver updates:

  • Nvidia DVD Zone
  • Nvidia geForce 256 FAQ
  • More to come...
[4.7] Можно ли передавать данные с DVD потоком по локальной сети или через интернет?

Short answer: usually not.

With a fast enough network (100 Mbps or better, with good performance and low traffic) and a high-performance server, it's possible to stream DVD-Video from a server to client stations. If the source on the server is a DVD-ROM drive (or jukebox), then more than one user simultaneously accessing the same disc will cause breaks in the video unless the server has a fast DVD-ROM drive and a very good caching system designed for streaming video.

A big problem is that CSS-encrypted movies (see 1.11) are difficult to remotely source because of security issues. The CSS license does not allow decrypted video to be sent over an accessible bus or network, so the decoder has to be on the remote PC. If the decoder has a secure channel to perform authentication with the drive on the server, then it's possible to stream encrypted video over a network to be decrypted and decoded remotely.

An alternative is to decode the video at the server and send it to individual stations via separate cables (usually RF). The advantage is that performance is very good, but the disadvantage is that that DVD interactivity is usually limited, and every viewer connected to a single drive/decoder must watch the same thing at the same time.

Many companies provide support for streaming MPEG-1 and MPEG-2 video over LANs, but only from files or realtime encoders, not from DVD-Video discs.

The Internet is a different matter. It takes over a week to download the contents of a single-layer DVD using a 56k modem. It takes about 7 hours on a T1 line. Cable modems theoretically cut the time down to a few hours, but if other users in the same neighborhood have cable modems, bandwidth could drop significantly. [Jim's prediction: the average DVD viewing household won't have sufficiently fast Internet connections before 2007 at the earliest. Around that time there will be a new high-definition version of DVD with double the data rate, which will once again exceed the capacity of the typical Internet connection.]

[4.8] Что такое DeCSS?

CSS (Content Scrambling System) is an encryption and authentication scheme intended to prevent DVD movies from being digitally copied. See 1.11 for details. DeCSS refers to the general process of defeating CSS, as well as to DeCSS source code and programs.

Computer software to decrypt CSS was released to the Internet in October 1999 (see Dana Parker's article at www.emediapro.net/news99/news111.html), although other "ripping" methods were available before that (see www.7thzone.com, go.to/dvdsoft, and www.neophile.net). The difference between circumventing CSS encryption with DeCSS and intercepting decrypted, decompressed video with a DVD ripper is that DeCSS can be considered illegal under the DMCA and the WIPO treaties. The DeCSS information can be used to "guess" at master keys, such that a standard PC can generate the entire list of 400 keys, rendering the key secrecy process useless.

In any case, there's not much appeal to being able to copy a set of movie files (without menus and other DVD special features) that would take over a week to download on a 56K modem and would fill up a 6G hard disk or a dozen CD-Rs. The supporters of DeCSS point out that it was only developed to allow DVD movies to be played on the Linux operating system, which had been excluded from CSS licensing because of its open-source nature. This is specifically allowed by DMCA and WIPO laws. What most DeCSS proponents fail to acknowledge (or perhaps fail to realize) is that the DeCSS.exe program being posted on the Internet is a Windows application that is clearly intended for copying movies. This lack of differentiation between the DeCSS process in Linux and the DeCSS.exe Windows application is hurting the cause of DeCSS backers. See OpenDVD.org for more information on DeCSS. 

Worthy of note is that DVD piracy was around long before DeCSS. Serious DVD pirates can copy the disc bit for bit, including the normally unreadable lead in (possible only with specially modified drives), or copy the video output from a standard DVD player, or get a copy of the video from another source such as laserdisc, VHS, or a camcorder smuggled into a theater. It's certainly true that DVD piracy is problem, but DeCSS has little to do with it. 

Shortly after the appearance of DeCSS, the DVD CCA filed a lawsuit and requested a temporary injunction in an attempt to prevent Web sites from posting (or even linking to!) DeCSS information. The request was denied by a California court on December 29, 1999. On January 14, 2000, the seven top U.S. movie studios (Disney, MGM, Paramount, Sony [Columbia/TriStar], Time Warner, Twentieth Century Fox, and Universal), backed by the MPAA, filed lawsuits in Connecticut and New York in a further attempt to stop the distribution of DeCSS on Web sites in those states. On January 21, the judge for the New York suit granted a preliminary injunction, and on January 24, the judge for the CCA suit in California reversed his earlier decision and likewise granted a preliminary injunction. In both cases, the judges ruled that the injunction applied only to sites with DeCSS information, not to linking sites. (Good thing, since this FAQ links to DeCSS sites!) The CCA suit is based on misappropriation of trade secrets (somewhat shaky ground), while the MPAA suits are based on copyright circumvention. On January 24, 16-year old Jon Johansen, the Norwegian programmer who first distributed DeCSS, was questioned by local police who raided his house and confiscated his computer equipment and cell phone. Johansen says the actual cracking work was done by two anonymous programmers, one German and one Dutch, who call themselves Masters of Reverse Engineering (MoRE).

This all seems to be a losing battle, since the DeCSS source code is available on a T-shirt and was made publicly available by the DVD CCA itself in court records--oops! See Fire, Work With Me for a facetious look at the broad issue.

[4.9] Как воспроизводить DVD в HTML, PowerPoint, Director, VB и т.д.?

A variety of multimedia development/authoring programs can be extended to play video from a DVD, either as titles and chapters from a DVD-Video volume, or as MPEG-2 files. In Windows, this is usually done with ActiveX controls. On the Mac, until DVD-Video support is added to QuickTime, the options are limited. 

DVD-Video and MPEG-2 video can be played back in an HTML page in Microsoft Internet Explorer using Windows Media Player (docs on DVD scripting are in the Windows Media SDK), InterActual PC Friendly, or SpinWare PortaLink. Netscape Navigator doesn't work, since it doesn't support ActiveX objects.

MPEG-2 video can be played in PowerPoint, Visual Basic, or other ActiveX hosts using Windows Media Player. Because of an annoying reliance on IE, WMP must be embedded into an HTML page, then controlled with the Browser ActiveX control in order to play DVD-Video. Zuma Digital's ActiveDVD (using the PC Friendly engine), Daikin's Enhanced DVD Kit (also using the PC Friendly engine), and Visible Lights' OnStage DVD ActiveX provide ActiveX-based DVD playback.

A number of Xtras are (or will soon be) available for DVD playback in Director. Tabuleiro's DirectMediaXtra plays MPEG-2 files (the older MpegXtra uses MCI, which doesn't work well for MPEG-2 and DVD). LBO's Xtra DVD and Visible Light's OnStage DVD Xtra plays DVD-Video volumes.

Of course, if you simply treat DVD-ROM as a bigger, faster CD-ROM, you can create projects using traditional tools (Director, Flash, Toolbook, HyperCard, VB, HTML, etc.) and traditional media types (CinePak, Sorenson, Indeo, etc. in QuickTime or AVI format) and they'll work just fine from DVD. You can even raise the data rate for bigger or better quality video. But it still won't look as good as MPEG-2.

[4.10] Что это за файлы - .IFO, .VOB и .AOB? Как их воспроизвести?

The DVD-Video and DVD-Audio specifications define how audio and video data are stored in specialized files. The .IFO (and backup .BUP) files contain menus and other information about the video and audio. The .VOB files (for DVD-Video) and .AOB files (for DVD-Audio) are MPEG-2 program streams with additional packets containing navigation and search information. 

Since a .VOB file is just a specialized MPEG-2 file, most MPEG-2 decoders and players can play them. However, any special features such as angles or branching will cause strange effects. The best way to play a .VOB file is to use a DVD player application to play the entire volume (or to open the VIDEO_TS.IFO file), since this will make sure all the DVD-Video features are used properly.

The DVD Video Recording format will introduce .SOB files <snigger>.

Most .VOB files won't play when copied to your hard drive. See 4.5.


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