LaCie D2 BLU-RAY XL User Manual - page 22
LaCie d2 Blu-ray Drive
Helpful Technical Information
User Manual
page 22
4.4. About BD/DVD/CD available
capacity
There are important factors to consider when recording video, audio
or data to CDs, DVDs or Blu-ray discs. The DVD media specification
provides for two physical sizes: 4.7” (12cm) and 3.1” (8cm) (both
are .47” (1.2cm) thick). Blu-ray and DVD discs are single-sided and
can have one (SL) or two (DL) layers of data.
The amount of data or video that a disc can hold are dependent
upon factors such as the amount of audio and the degree of com-
pression of the data, video or audio. For example, a double-layer
BD-R will store just over 4 hours of HD video using MPEG2, but it
is possible to store up to 20 hours of broadcast quality standard
definition video.
When media companies reference the amount of data that a disc
can hold, they represent the total amount in terms of gigabytes
(GB), or a billion bytes (1000 x 1000 x 1000 bytes). This number,
though, is not the way in which a computer addresses the data;
to a computer the value is binary and larger than a billion bytes –
1,073,741,824 (1024 x 1024 x 1024 bytes).
4.5. About compression standards
Most of the Blu-ray Video material and all the DVD-Video materials
are compressed using MPEG2 codec. The acronym MPEG stands
for Moving Picture Expert Group, which worked to generate com-
pression specifications under ISO. What is commonly referred to as
“MPEG video” actually consists at the present time of three finalized
standards, MPEG1, MPEG2, MPEG4 which was finalized in 1998
for Very Low Bitrate Audio-Visual Coding.
HD Video, with full-motion video and multi-channel sound (multi-
lingual soundtracks, surround sound, etc.), is a data-hungry appli-
cation. MPEG2 compression allows you to fit a full-length feature
film in HD, plus bonus material, on just one disc. MPEG4 AVC
(H.264) and VC-1 are two other HD video compression standards
which can match the best possible MPEG2 quality at up to half the
data rate. But they are not not much used by the professional video
industry yet.
Indication of bit rates for HD Video:
✦
MPEG2 = 21Mbits/s
✦
MPEG4 (H.264) = 8Mbits/s
✦
VC-1(WMV9) = 8 Mbits/s