DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Concerning the formation of
coded macroblocks in DV, see
DV compression, on page 461.
DV recording
For recording on tape, a video sync block is assembled
from 5 bytes of sync/ID information, a compressed
(“coded”) macroblock (CM), and an inner error detection
and correction (EDC) code. The ID portion of the
sync block header encodes the position in the image of
the associated CM.
A sequence of 135 video sync blocks, augmented by
video auxiliary (VAUX) data and outer EDC codes, forms
a video sector. All of the elements of the sector are
randomized through a prescribed pattern of exclusiveor
operations. The serialized bitstream is augmented by
an extra bit (EB) every 24th data bit; the extra bit is
used to insert pilot tones (F0, F1, F2) used for tracking.
An audio sector is constructed similarly, but using audio
samples and audio auxiliary (AAUX) data.
Video and audio are recorded on separate sectors, with
an intersector gap; the gap enables video and audio to
be edited separately. A track commences with a short
insert and track information (ITI) sector that provides
control information to enable insert editing. Every track
ends with a subcode sector that provides control and
timecode functions.
For DV25, the aggregate data rate on tape is about
about 40 Mb/s. DV25 480i SDTV requires 10 tracks
(i.e., head passes) per frame; DV25 576i SDTV requires
12 tracks per frame. In consumer DV, such a recording
(with standard 10 µm track pitch) is termed standard
definition (SD) mode.
LP refers to long play mode, sometimes referred to as
LP mode, narrow track pitch. LP mode is virtually identical
to SD mode, except that track pitch is reduced
from the usual 10 µm to 6.67 µm, and tape speed is
correspondingly reduced. This yields 1.5 times the
recording time of SD for a given tape length. Not all
consumer DV products offer this mode.
Sony has adapted DV25 coding to the 8 mm tape
format, for consumer use; this is called Digital8. Tape
424 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES