In a BDMV application, memory is divided into three buffers: a Primary, Secondary, and Preloading

There is also two switches. The first switch (SW1) between the switch before the buffers selects the appropriate buffer to receive demodulated packet data from
the BD-ROM Drive or Local Storage.

The Preloading Buffers are responsible for storing data, fonts, graphics, and sounds, and is the first to be loaded before the Primary Read Buffer.

On the other hand, the Primary Read Buffer (RB1) stores the video and audio bitrate, as well as the on-screen presentation graphics for subtitles, and is loaded last.

The Second Read Buffer (RB2) enables the supply of an an Out-of-Mux audio stream to the decoder even while the main MPEG stream is being decoded thanks to the second switch (SW2). For example, a Browsable Slideshow with background music, the switch selects the Secondary Read Buffer (RB2) to store an Out-of-Mux audio stream and continue supplying the audio stream to the decoder. It is unknown if this works with fonts and graphics since it's supported on UHD-BD (Profile 6.0). However, it is possible to load data to the buffers/cache from local storage without interfering with disc playback.

BD's decoder model

Memory Limitations

Media Type	Description	Buffer Size
Primary Video	Main video for a movie, video background, or still-images. Normally played from the disc. Stored in the primary read buffer.	5 MB (40 Mbps)*
Primary Audio	Main soundtrack for a movie, music album, or video game. Normally played from the disc. Stored in the primary read buffer. It can also be stored in the secondary read buffer.	5 MB (40 Mbps)†
Secondary Video	Provides Picture-in-Picture video in front of the Primary Video. Normally played from local storage. Stored in the primary read buffer.	3.456 MB (27.648 Mbps)*
Secondary Audio	Audio for the secondary video; can also be used for additional audio for video games. Normally played from local storage. Stored in the primary read buffer.	32 KB (256 Kbps)†
Presentation Graphics/Text Fonts	Both formats used for subtitles, displaying text, or decorations. Both formats cannot be displayed at the same time. PGs are stored in the primary memory buffer. Text fonts are stored in the second preloading memory buffer.	4MB
Interactive/BD-J Graphics	Used for store graphics and sprites for interactive menus, video games, and interactive programs. Stored in the second preloading memory buffer.	16MB (HDMV)/45.5MB (BD-J)**
Interactive Sound	Used for interactive audio for menus and video games. Stored in the first preloading memory buffer.	2MB
Data Cache	Data for a BD-J application (JAR files(s) are stored here). (It is unknown if the Index file, Clips, Playlists, and Object files are stored here, in their own separate memory cache, or only read from the disc once.)	4MB

* The maximum memory for simultaneous playback of Primary Video and Audio is 6 MB (48 Mbps). In Profile 5.0 (3D) players, MVC Dependent view (left-eye) is 5 MB (40 Mbps), the maximum memory for simultaneous playback of both the left-eye and right-eye for 3D video is 60Mbps (7.5 MB).

** Players with Profile 2.0 and 5.0 have an additional 15 MB of graphics memory for BD-J, totaling 61.5 MB. However, it's strongly advised to stick with the standard 45.5 MB to ensure compatibility with Profile 1.1 players, unless it's being used for an application that requires a LAN/online connection (e.g. Multiplayer) and Stereo 3D content.

† Secondary Video and Audio is not available on Ultra HD Blu-ray (Profile 6.0)

 

Item Limitations

Besides memory, developers also have to deal with the limitations of video and data items.

Item	Max Number of Items
Angles	9
Audio Streams (Primary)	32
Audio Streams (Secondary)	32
Chapters	999
Clips	4000
Objects	1001
Interactive Graphics Streams	32
Playlists	2000
Subtitles	32
Titles	999
Sounds	128

Sources

• Scenarist BD Development manual, Doom9 forums, BD-ROM Whitepaper (2010), and original research.
• HDCookbook - Page 21-1 "BD-J File I/O"
  
• Hughnews.ca
  

Author(s) : Æ Firestone