Blu-ray Disc (official abbreviation BD) is an optical disc storage medium designed to supersede the DVD format. The disc diameter is 120 mm and disc thickness 1.2 mm plastic optical disc, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB (23.31 GiB) per layer, with dual layer discs (50 GB) being the norm for feature-length video discs. Triple layer discs (100 GB) and quadruple layers (128 GB) are available for BD-XL Blu-ray re-writer drives. Currently movie production companies have not utilized the triple or quadruple layer discs; most consumer owned Blu-ray players will not be able to read the additional layers, while newer Blu-ray players may require a firmware update to play the triple and quadruple sized discs.

The name Blu-ray Disc refers to the blue laser used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs.

Blu-ray Disc was developed by the Blu-ray Disc Association, a group representing makers of consumer electronics, computer hardware, and motion pictures.

While a DVD uses a 650 nm red laser, Blu-ray Disc uses a 405 nm “blue” laser diode. Note that even though the laser is called “blue”, its color is actually in the violet range. The smaller beam focuses more precisely, thus enabling it to read information recorded in pits that are less than half the size of those on a DVD, and can consequently be spaced more closely, resulting in a shorter track pitch, enabling a Blu-ray Disc to hold about five times the amount of information that can be stored on a DVD.

The lasers are GaN (gallium nitride) laser diodes that produce 405 nm light directly, that is, without frequency doubling or other nonlinear optical mechanisms. Conventional DVDs use 650 nm red lasers, and CDs use 780 nm near-infrared lasers.

The minimum “spot size” on which a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85, and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller spot, which effectively allows more information to be stored in the same area.

Since the Blu-ray Disc data layer is closer to the surface of the disc compared to the DVD standard, it was at first more vulnerable to scratches. The first discs were housed in cartridges for protection, resembling Professional Discs introduced by Sony in 2003.

Using a cartridge would increase the price of an already expensive medium, so hard-coating of the pickup surface was chosen instead. TDK was the first company to develop a working scratch-protection coating for Blu-ray Discs. It was named Durabis. In addition, both Sony and Panasonic’s replication methods include proprietary hard-coat technologies. Sony’s rewritable media are spin-coated, using a scratch-resistant and antistatic coating. Verbatim’s recordable and rewritable Blu-ray Discs use their own proprietary hard-coat technology, called ScratchGuard.

The Blu-ray Disc specification requires the testing of resistance to scratches by mechanical abrasion. In contrast, DVD media are not required to be scratch-resistant, but since development of the technology, some companies, such as Verbatim, implemented hard-coating for more expensive lineups of recordable DVDs.

The “Mini Blu-ray Disc” (also, “Mini-BD” and “Mini Blu-ray”) is a compact 8 cm (~3 in)-diameter variant of the Blu-ray Disc that can store approximately 7.5 GB of data. It is similar in concept to the MiniDVD and MiniCD. Recordable (BD-R) and rewritable (BD-RE) versions of Mini Blu-ray Disc have been developed specifically for compact camcorders and other compact recording devices

“Blu-ray Disc recordable” refers to two optical disc formats that can be recorded with an optical disc recorder. BD-Rs can be written to once, whereas BD-REs can be erased and re-recorded multiple times. The current practical maximum speed for Blu-ray Discs is about 12×. Higher speeds of rotation (10,000+ rpm) cause too much wobble for the discs to be read properly, as with the 20× and 52× maximum speeds, respectively, of standard DVDs and CDs.

The BD9 format was proposed to the Blu-ray Disc Association by Warner Home Video as a cost-effective alternative to the 25/50 GB BD-ROM discs. The format was supposed to use the same codecs and program structure as Blu-ray Disc video, but recorded onto less expensive 8.5 GB dual-layer DVD. This red-laser media could be manufactured on existing DVD production lines with lower costs of production than the 25/50 GB Blu-ray media.

Usage of BD9 for releasing content on “pressed” discs has never caught on. After the end of the format war, major producers ramped up the production of Blu-ray Discs and lowered their prices to the level of DVDs. On the other hand, the idea of using inexpensive DVD media became popular among individual users. A lower-capacity version of this format that uses single-layer 4.7 GB DVDs has been unofficially called BD5. Both formats are being used by individuals for recording high definition content in Blu-ray format onto recordable DVD media.

Despite the fact that the BD9 format has been adopted as part of the BD-ROM basic format, none of the existing Blu-ray player models support it explicitly. As such, the discs recorded in BD9 and BD5 formats are not guaranteed to play on standard Blu-ray Disc players.

AVCHD and AVCREC also use inexpensive media like DVDs, but unlike BD9 and BD5 these formats have limited interactivity, codec types, and data rates.

The BDXL format supports 100GB and 128GB write-once discs and 100GB rewritable discs for commercial applications. It was defined in June 2010.

BD-R 3.0 Format Specification (BDXL) defined a multi-layered disc recordable in BDAV format with the speed of 2X and 4X, capable of 100/128GB and usage of UDF2.5/2.6.

BD-RE 4.0 Format Specification (BDXL) defined a multi-layered disc rewritable in BDAV with the speed of 2X and 4X, capable of 100GB and usage of UDF2.5 as file system.

BDXL discs are not compatible with existing BD drives.

The IH-BD (Intra-Hybrid Blu-ray) format includes a 25GB write-once layer (BD-R) and a 25GB read-only layer (BD-ROM), designed to work with existing Blu-ray Discs.

Blu-ray Disc specifies the use of Universal Disk Format (UDF) 2.50 as a convergent friendly format for both PC and consumer electronics environments. It is used in latest specifications of BD-ROM, BD-RE and BD-R.

The Blu-ray Disc application (BDAV application) for recording of digital broadcasting has been developed as System Description Blu-ray Rewritable Disc Format part 3 Audio Visual Basic Specifications. The requirements related with computer file system have been specified in System Description Blu-ray Rewritable Disc Format part 2 File System Specifications version 1.0 (BDFS).

All BD-ROM application files are stored under a “BDMV” directory.

BDMV directory: contains the PLAYLIST, CLIPINF, STREAM, AUXDATA and BACKUP directories.

PLAYLIST directory: contains the Database files for Movie PlayLists.

xxxxx.mpls files: store information corresponding to Movie PlayLists. One file is created for each Movie PlayList. The filenames of these files are in the form “xxxxx.mpls”, where “xxxxx” is a 5-digit number corresponding to the Movie PlayList.

CLIPINF directory: contains the Database files for Clips.

zzzzz.clpi files: store Clip information associated with a Clip AV stream file. The filenames of these files are in the form “zzzzz.clpi”, where “zzzzz” is a 5-digit number corresponding to the Clip.

STREAM directory: contains AV stream files.

zzzzz.m2ts file: contains a BDAV MPEG-2 transport stream. The names of these files are in the form “zzzzz.m2ts”, where “zzzzz” is a 5-digit number corresponding to the Clip. The same 5-digit number “zzzzz” is used for an AV stream file and its associated Clip information file.

SSIF directory: If used, Stereoscopic Interleaved files shall be placed under this directory.

zzzzz.ssif file: is a Stereoscopic Interleaved file that is composed from two BDAV MPEG-2 transport streams. Both of the streams include an MPEG-4 MVC view video stream for left eye or right eye respectively. This file is used only when 3D video is played back. The 5-digit number “zzzzz” is the same as the number used for the AV stream file “zzzzz.m2ts” that includes the MPEG-4 MVC Base view video stream.

AUXDATA directory: contains Sound data files and Font files.

sound.bdmv file: stores data relating to one or more sounds associated with HDMV Interactive Graphic streams applications. This file may or may not exist under the AUXDATA directory. If it exists, there shall be only one sound.bdmv file.

aaaaa.otf file: stores the font information associated with Text subtitle applications. The names of these files are in the form “aaaaa.otf”, where “aaaaa” is a 5-digit number corresponding to the Font.

BACKUP directory: contains copies of the “index.bdmv” file, the “MovieObject.bdmv” file, all the files in the PLAYLIST directory and all files in the CLIPINF directory.

index.bdmv file: stores information describing the contents of the BDMV directory. There is only one index.bdmv file under the BDMV directory.

MovieObject.bdmv file: stores information for one or more Movie Objects. There is only one MovieObject.bdmv under the BDMV directory.

Audio, video and other streams are multiplexed and stored on Blu-ray Discs in a container format based on the MPEG transport stream. It is also known as BDAV MPEG-2 transport stream and can use filename extension .m2ts. Blu-ray Disc titles authored with menu support are in the BDMV (Blu-ray Disc Movie) format and contain audio, video, and other streams in BDAV container.

There is also the BDAV (Blu-ray Disc Audio/Visual) format, the consumer oriented alternative to the BDMV format used for movie releases. The BDAV format is used on BD-REs and BD-Rs for audio/video recording.

BDMV format was later defined also for BD-RE and BD-R (in September 2006, in the third revision of BD-RE specification and second revision of BD-R specification). Blu-ray Disc employs the MPEG transport stream recording method. That enables transport streams of digital broadcasts to be recorded as they are without altering the format. It also enables flexible editing of a digital broadcast that is recorded as is and where the data can be edited just by rewriting the playback stream. Although it is quite natural, a function for high-speed and easy-to use retrieval is built in. Blu-ray Disc Video use MPEG transport streams, compared to DVD’s MPEG program streams. This allows multiple video programs to be stored in the same file so they can be played back simultaneously (e.g., with “Picture in picture” effect).

The BD-ROM specification mandates certain codec compatibilities for both hardware decoders (players) and movie software (content).

High-definition video may be stored on BD-ROMs with up to 1920×1080 pixel resolution at up to 59.94 fields per second, if interlaced. Alternatively, progressive scan can go up to 1920×1080 pixel resolution at 24 frames per second, or up to 1280×720 at up to 59.94 frames per second

For audio, BD-ROM players are required to support Dolby Digital (AC-3), DTS, and linear PCM. Players may optionally support Dolby Digital Plus and DTS-HD High Resolution Audio as well as lossless formats Dolby TrueHD and DTS-HD Master Audio. BD-ROM titles must use one of the mandatory schemes for the primary soundtrack. A secondary audiotrack, if present, may use any of the mandatory or optional codecs.

For users recording digital television programming, the recordable Blu-ray Disc standard’s initial data rate of 36 Mbit/s is more than adequate to record high-definition broadcasts from any source (IPTV, cable/satellite, or terrestrial). BD Video movies have a maximum data transfer rate of 54 Mbit/s, a maximum AV bitrate of 48 Mbit/s (for both audio and video data), and a maximum video bit rate of 40 Mbit/s. This compares to HD DVD movies, which have a maximum data transfer rate of 36 Mbit/s, a maximum AV bitrate of 30.24 Mbit/s, and a maximum video bitrate of 29.4 Mbit/s

Java is used to implement interactive menus on Blu-ray Discs, as opposed to the method used on DVD-video discs. DVDs use pre-rendered MPEG segments and selectable subtitle pictures, which are considerably more primitive and rarely seamless.

The BD-ROM specification defines four Blu-ray Disc player profiles, including an audio-only player profile (BD-Audio) that does not require video decoding or BD-J. All three of the video-based player profiles (BD-Video) are required to have a full implementation of BD-J, with varying levels of hardware support.

As with the implementation of region codes for DVDs, Blu-ray Disc players sold in a specific geographical region are designed to play only discs authorized by the content provider for that region. This is intended to permit content providers (motion picture studios, etc.) the ability to support product differences in content, price, release date, etc., by region. According to the Blu-ray Disc Association, “all Blu-ray Disc players…(and) Blu-ray Disc-equipped computer systems are required to support regional coding.” However, “Use of region playback codes is optional for content providers…” Some current estimates suggest 70% of available [movie] Blu-ray Discs from the major studios are region-code-free and can therefore be played on any Blu-ray Disc player, in any region.

The Blu-ray Disc region coding scheme divides the world into 3 regions, labeled A, B, and C.

* Region A includes most North, Central and South American and Southeast Asian countries plus the Republic of China (Taiwan), Japan, Hong Kong, Macau and Korea.
* Region B includes most European, African and southwest Asian countries plus Australia and New Zealand.
* Region C contains the remaining central and south Asian countries, as well as the People’s Republic of China and Russia.

The Blu-ray Disc format employs several layers of digital rights management (DRM).

Blu-ray equipment is encouraged to implement High-bandwidth Digital Content Protection (HDCP). Given certain flags in the media streams, a Blu-ray Disc can enforce its reproduction in a lower resolution whenever a full HDCP-compliant link is not established all the way from the Blu-ray drive to the rendering devices (i.e. display and speakers).

BD+ was developed by Cryptography Research Inc. and is based on their concept of Self-Protecting Digital Content. BD+, effectively a small virtual machine embedded in authorized players, allows content providers to include executable programs on Blu-ray Discs. Such programs can:

* examine the host environment to see if the player has been tampered with. Every licensed playback device manufacturer must provide the BD+ licensing authority with memory footprints that identify their devices.
* verify that the player’s keys have not been changed.
* execute native code, possibly to patch an otherwise insecure system.
* transform the audio and video output. Parts of the content will not be viewable without letting the BD+ program unscramble it.

If a playback device manufacturer finds that its devices have been hacked, it can potentially release BD+ code that detects and circumvents the vulnerability. These programs can then be included in all new content releases.

BD-ROM Mark is a small amount of cryptographic data that is stored separately from normal Blu-ray Disc data. Bit-by-bit copies that do not replicate the BD-ROM Mark have no known decoding method. A specially licensed piece of hardware is required to insert the ROM-mark into the media during replication.

AVCHD was originally developed as a high definition format for consumer tapeless camcorders. Derived from the Blu-ray Disc specification, AVCHD shares a similar random access directory structure, but is restricted to lower audio and video bitrates, simpler interactivity, and the use of AVC-video and Dolby AC-3 (or linear PCM) audio.

Being primarily an acquisition format, AVCHD playback is not universally supported by all devices that support Blu-Ray Disc playback. Nevertheless, many such devices are capable of playing AVCHD recordings from removable media, such as DVDs, SD/SDHC memory cards, “Memory Stick” cards, and hard disk drives

AVCREC uses a BDAV container to record high definition content on conventional DVDs. Presently AVCREC is tightly integrated with the Japanese ISDB broadcast standard and is not marketed outside of Japan. AVCREC is used primarily in set-top digital video recorders and in this regard is comparable to HD REC.


Feature BD-Audio BD-Video
Grace Period Bonus View BD-Live Blu-ray 3D
Profile 3.0 Profile 1.0 Profile 1.1 Profile 2.0 Profile 5.0
Built-in persistent memory No 64 KB 64 KB 64 KB 64 KB?
Local storage capability No Optional 256 MB 1 GB 1 GB
Secondary video decoder (PiP) No Optional Mandatory Mandatory Mandatory
Secondary audio decoder No Optional Mandatory Mandatory Mandatory
Virtual file system No Optional Mandatory Mandatory Mandatory
Internet connection capability No No No Mandatory Mandatory


Specification of BD-ROM Primary audio streams:

LPCM Dolby Digital Dolby Digital Plus Dolby TrueHD (Lossless) DTS Digital Surround DTS-HD Master Audio (Lossless) DRA DRA Extension
Max. Bitrate 27.648 Mbit/s 640 kbit/s 4.736 Mbit/s 18.64 Mbit/s 1.524 Mbit/s 24.5 Mbit/s 1.5 Mbit/s 3.0 Mbit/s
Max. Channel 8 (48 kHz, 96 kHz), 6 (192 kHz) 5.1 7.1 8 (48 kHz, 96 kHz), 6 (192 kHz) 5.1 8 (48 kHz, 96 kHz), 6 (192 kHz) 5.1 7.1
Bits/sample 16, 20, 24 16, 24 16, 24 16, 24 16, 20, 24 16, 24 16 16
Sample frequency 48 kHz, 96 kHz, 192 kHz 48 kHz 48 kHz 48 kHz, 96 kHz, 192 kHz 48 kHz 48 kHz, 96 kHz, 192 kHz 48 kHz 48 kHz, 96 kHz


Resolution Frame rate Aspect ratio
1920×1080 29.97-i 16:9
1920×1080 25-i 16:9
1920×1080 24-p 16:9
1920×1080 23.976-p 16:9
1440×1080 29.97-i 16:9 (anamorphic)
1440×1080 25-i 16:9 (anamorphic)
1440×1080 24-p 16:9 (anamorphic)
1440×1080 23.976-p 16:9 (anamorphic)
1280×720 59.94-p 16:9
1280×720 50-p 16:9
1280×720 24-p 16:9
1280×720 23.976-p 16:9
720×480 29.97-i 4:3/16:9 (anamorphic)
720×576 25-i 4:3/16:9 (anamorphic)


Drive speed Data rate Theoretical Write time for Blu-ray Disc (minutes)
Mbit/s MB/s Single-Layer Dual-Layer
36 4.5 90 180
72 9 45 90
144 18 22.5 45
216 27 15 30
288 36 11.25 22.5
10× 360 45 9 18
12× 432 54 7.5 15


Type Diameter
Layers Capacity
Bytes GB GiB
Standard disc size, single layer 12 1 25,025,314,816 25.0 23.3
Standard disc size, dual layer 12 2 50,050,629,632 50.1 46.6
Mini disc size, single layer 8 1 7,791,181,824 7.8 7.3
Mini disc size, dual layer 8 2 15,582,363,648 15.6 14.5

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