IMPORTANT NOTE

I am now working under NDA with a BD-J content and tools developer and can no longer update this page.

About

There are three very different specifications for Blu-Ray: BD-ROM (read-only), BD-R (recordable), and BD-RE (rewritable). Each specification is tailored for a specific use and has a unique file structure on the disc.

Prerecorded movie titles are distributed as BD-ROM discs. From what I can tell, BD-ROM is the only specification that supports Blu-Ray interactive applications. However, I have observed that you can put BD-ROM files on a BD-RE disc and it will behave like a BD-ROM disc.

The Blu-Ray BD-ROM specification defines the BD-J interactive application environment. It’s based on DVB-MHP GEM 1.0.2 interactive TV specification, which uses Java as its programming language. Blu-Ray extends the GEM environment to provide Blu-Ray specific functionality. The Blu-Ray Disc Association offers some technical white papers which give an overview of the Blu-Ray technologies.

Sadly, the Blu-Ray specifications are very expensive and there is no third-party documentation on the Blu-Ray specific APIs. I take this to mean there is no legal way to use the Blu-Ray specific APIs without purchasing a specification and/or license.

There are also no public details about how to sign a BD-J .jar file. Signing gives access to additional features (network connectivity, access to local storage, cross-disc application lifespan). I assume the signing procedure is similar to J2ME, but I do not know what certificate signing authorities are trusted, and therefore where one would go to procure a legitimate signing certificate. I also do not know what permission strings are required to enable these features, or where I would put them (in the .jar manifest?).

Lastly, there are no publicly available simulators targeted at BD-J. I have found simulators oriented toward MHP and GEM, but those simulators are seemingly limited to standard-definition resolutions and do not implement the Blu-Ray APIs. I will experiment further.

Getting Started

I have pursued a Windows build environment, because my Blu-Ray playback environment is also Windows. But I see no theoretical reason why the following steps would not work as well under Linux.

• Java SE JDK 5.0 (latest update — I used “10″)
• Eclipse SDK 3.2.1
• OpenMHP 1.0.4 binary package (free registration required)
• JavaTV 1.1_01 binary reference implementation. It’s currently available only for Linux, but that’s OK because we’ll only use the .jars to compile against.
• Personal Basis Profile 1.1 binary reference implementation (free registration required). This is also available only for Linux, but is fine to compile against.

Install the Java SE JDK and the bundled JRE.
Install (unzip) Eclipse.
Install (unzip) OpenMHP.
Install (unzip) the JavaTV binary package contained within the binary/documentation package.
Install (unzip) the Personal Basis Profile.

Start Eclipse and create a project which references javatv.jar from the JavaTV reference implementation, and basis.jar and btclasses.zip from the Personal Basis Profile. (TODO: instructions to .zip/.jar the OpenMHP classes for referencing.)

It’s crucial to change your “Java Compiler” settings to use compiler compliance level 1.4. If you use 5.0, the classes apparently won’t load. This suggests that the BD-J implementations are based on Java 1.4, and that compiling under a newer JDK introduces new features that older VMs can’t handle.

Create a .jar file: jar cvf app.jar *.class

Video/Audio Media

Preparation of media is beyond my intended scope. But I am experimenting with Apple’s Compressor and its HD DVD MPEG-2 output template. Many of Sony’s first Blu-Ray releases use MPEG-2, and it’s a lot easier to find programs that encode MPEG-2 at HD resolutions than it is to find VC-1 encoders (although I haven’t tried all that hard yet). Besides, for my experiments, I don’t care too much about video quality.

Filesystem

There are a few critical files that must be in place for a BD-J application to load from a BD-ROM filesystem:

• BDMV\index.bdmv: contains a list of titles on the disc, and also specifies what content object gets run first, and which content object acts as the top menu for the disc. Content objects can be movie objects (which implement DVD-style menus) or BD-J objects (which refer to BD-J applications).
• BDMV\BDJO\*.bdjo: A file representing a single BD-J application. A .bdjo file appears to contain filename patterns of files to preload (usually .jar files), the name of the .jar file that contains the application’s Xlet class, and the name of the Xlet class. There also seems to be some sort of search/classpath. And I see some characters that appear to be a language tag (for localizing BD-J applications?) and an application name (for display to the user?). Many of the strings are stored Pascal-style, with a preceeding byte indicating the length of the string. Starting at byte 8 of a .bdjo file, there appears to be a series of monotonically-increasing 4-byte pointers into the rest of the file.
• BDMV\JAR\*.jar: Java .jar files containing the usual bundle of Java .class files and associated application resources.

Other files are involved in media playback:

• BDMV\PLAYLIST\*.mpls: in progress…
• BDMV\CLIPINF\*.clpi: in progress…

Many of the files have the following, semi-obvious structure:

Header
• 4 bytes: file type
• 4 bytes: specification revision
• 8 * 4 bytes: absolute pointer into file (chunks 2 through 9), or zero if unused
• n bytes: first chunk (not referenced in prior pointer list)

Chunk
• 4 bytes: chunk length, not including this field
• n bytes: varies per chunk type, in progress…

Some files terminate with one or more empty (four-byte) chunks. Other files just have extraneous bytes. The empty chunks would mean something if they were non-empty. This implies that the ordinal of the pointers at the beginning of the file might indicate what type of chunk is referenced.

I have found one case where the above chunk format does not seem to apply. In .bdjo files, sixth chunk (which looks like a Pascal-string Java classpath) doesn’t seem to have a length field. Instead, I’m guessing the sixth chunk is always known to be a particular type of data, and that chunk data extends to the end of the file.

I’m going to write a Python script to explode these various data files into separate files (one for each chunk of data). I’ll post that soon.

If, like me, you do not have a copy of the BD-ROM specification, the easiest way to get a BDMV file system is to copy one from a commercial Blu-Ray BD-J-enhanced movie disc. You’ll have to replace all of the video streams in BDMV\STREAMS (which are protected by AACS content protection) with unprotected placeholder streams. I made myself a BD-RE disc (using Blu-Ray authoring software) with some short HDV placeholder video clips, then replaced all of the files on the movie filesystem with copies of my placeholder video. This probably breaks the disc’s playlists, but doesn’t have any ill effect on the software player I’m using. Now that there are no protected streams on your filesystem, you may delete the AACS and CERTIFICATE folders if desired.

The commercial BD-J movies I have seen are set up to load BDMV\JAR\00001.jar (which is a BD-J menu) when the disc is first inserted. So you’ll replace that .jar file with your new .jar file.

Running Your Application

If you’re using a PC-based software Blu-Ray player, you can launch it against the filesystem without burning to disc first. This really tightens the development cycle.

With any luck, your application will load and run. If it doesn’t, well, your debugging tools are stone-age. The software player I’m using has no obvious debug output, and I would imagine that commercial hardware players do not have any sort of accessable debug output. Of course, I could be wrong… That would be nice.

Call For Help

If you’re working with BD-J and have any revelations you’d like to share, please leave a comment and I’ll incorporate it into this document. I’d particularly like information on:

• Hardware players supporting BD-J, and does the methodology I describe above work for these players?
• Additional titles using BD-J. For now, the only titles I have personally verified are “League of Extraordinary Gentlemen” and “Speed”, both recent releases by Fox Home Entertainment. The fastest way to tell if a Blu-Ray movie contains BD-J content is to examine the disc filesystem. If there are .jar files in BDMV\JAR\, the disc has BD-J applications.
• Reverse-engineering insight into the structure of index.bdmv, MovieObject.bdmv, and .bdjo files. These files determine what titles are available on the disc, which one(s) are loaded initially, and which BD-J application(s) are executed with which titles. For reverse-engineering files under Windows, I recommend Hexplorer (see below). In my interpretation, I don’t see any conflict with the DMCA. The files relating to BD-J are not protected by any mechanism other than a lack of documentation, and there’s some public documentation of these files by Sun and the Blu-Ray Association. If you have a different opinion, please share it.

Links and References

• Blu-Ray Application Development using Java ME
• Java Technology Goes to the Movies: Java Technology in Next-Generation Optical Disc Formats (2005)
• Java�Ѣ Technology Goes to the Movies: Java Technology in Next-Generation Optical Disc Formats (2006)
• Hexplorer - a binary file viewer that, once a few tweaks to font color/size are made, is quite usable.