Blu Ray Codec Primer
Current Blu Ray Disc Burners: Sony BWU 200S | Plextor PX900a
Codecs are compression schemes that can be used to store
audio and video information on a disc. The BD-ROM specification
places requirements on both hardware decoders (players) and
the movie-software (content).
For video, ISO MPEG-2, H.264/AVC, and SMPTE VC-1 are player-mandatory.
(This means all BD-ROM players must be capable of decoding
all three video codecs.) MPEG-2 video allows decoder backward
compatibility for DVDs. H.264, sometimes called MPEG-4 part
10, is a more recent video codec developed jointly by the
same organization (ISO/IEC) as MPEG-2. VC-1 is a competing
MPEG-4 derivative codec proposed by Microsoft (based on Microsoft's
previous work in Windows Media 9). BD-ROM titles with video
must store video using one of the three mandatory codecs
(multiple codecs on a single title are legal).
Initial versions of Sony's Blu-ray Disc-authoring software
only included support for MPEG-2 video, so the initial Blu-ray
Discs were forced to use MPEG-2 rather than the newer codecs,
VC-1 and H.264. An upgrade was subsequently released supporting
the newer compression methods so the second wave of Blu-ray
Disc titles were able to make use of this. The choice of
codecs affects disc cost (due to related licensing/royalty
payments) as well as program capacity. The two more advanced
video codecs can typically achieve twice the video runtime
of MPEG-2. When using MPEG-2, quality considerations would
limit the publisher to around two hours of high-definition
content on a single-layer (25 GB) BD-ROM.
For audio, BD-ROM players are required to support Dolby
Digital AC-3, DTS, and linear PCM (up to 7.1 channels). Dolby
Digital Plus, and lossless formats Dolby TrueHD and DTS HD
are player optional. BD-ROM titles must use one of mandatory
audiotracks for the primary soundtrack (linear PCM 5.1, Dolby
Digital 5.1 or DTS 5.1.). A secondary audiotrack, if present,
may use any of the mandatory or optional codecs.[8] For lossless
audio in movies in the PCM, Dolby TrueHD or DTS-HD formats,
Blu-ray Discs support encoding in up to 24-bit/192 kHz for
up to six channels, or up to eight channels of up to 24-bit/96
kHz encoding.[9] For reference, even new big-budget Hollywood
films are mastered in only 24-bit/48 kHz, with 16-bit/48
kHz being common for ordinary films.
What is a Blu-ray Disc?
A current, single-sided, standard DVD can hold 4.7 GB (gigabytes) of information.
That's about the size of an average two-hour, standard-definition
movie with a few extra features. But a high-definition
movie, which has a much clearer image (see How Digital
Television Works),
takes up about five times more bandwidth and therefore
requires a disc with about five times more storage. As TV
sets and
movie studios make the move to high definition, consumers
are going to need playback systems with a lot more storage
capacity.
Blu-ray is the next-generation digital video disc. It can
record, store and play back high-definition video and digital
audio, as well as computer data. The advantage to Blu-ray
is the sheer amount of information it can hold:
- A single-layer Blu-ray disc, which is roughly
the same size as a DVD, can hold up to 27 GB of data --
that's more than two hours of high-definition video or
about 13 hours of standard video.
- A double-layer Blu-ray disc can store up to 50
GB, enough to hold about 4.5 hours of high-definition
video or more than 20 hours of standard video.
And there are even plans in the works to develop a disc
with twice that amount of storage.
