DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

The downsampling inherent in D-12
compression of 1080i means that
luma sample aspect ratio is effectively
3 ⁄2 (and chroma subsampling
is equivalent to 3:1:1) relative to the
original 1920×1080 image array.
The D-12 format, introduced by Panasonic as
DVCPRO HD, adapts DV technology to 100 Mb/s
(DV100), to compress and record 720p or 1080i HDTV.
The D-12 compression system is based upon
1280×1080 image format and 4:2:2 chroma subsampling
for 1080i or 1080p, or 960×720 image format
and 4:2:2 chroma subsampling for 720p. Video interfaces
in D-12 equipment are typically either 1080i30,
or 720p at any of several different frame rates.
DV digital interface (DIF)
The superblocks that I have mentioned form the basis
for digital interface of DV bitstreams. A 3-byte ID is
prepended to each 77-byte coded macroblock to form
an 80-byte digital interface (DIF) block.
A coded DV25 superblock is represented by 135 video
DIF blocks. That is augmented with several nonvideo
DIF blocks to form a DIF sequence of 150 DIF blocks:
• 1 header DIF block
• 2 subcode DIF blocks
• 3 VAUX DIF blocks
• 9 audio DIF blocks
• 135 video DIF blocks
Realtime DV25 video requires 10 or 12 DIF sequences –
that is, about 1500 or 1800 DIF blocks – per second.
DV12 1 ⁄2 (SDL), DV HD, DV50, and DV100 systems
have comparable structures, but different data rates.
The major parameters for consumer systems are
summarized in Table 39.2, on page 468.
Once packaged in DIF sequences, DV bitstreams can be
conveyed across the IEEE 1394 interface, also known as
FireWire and i.LINK, that I described on page 133. This
interface is widely used in desktop video, and is suitable
for consumer use. Studio video distribution equipment
has been introduced using this interface.
For professional applications, DIF sequence bitstreams
can be transported across the SDTI interface that
I introduced on page 132. (The 3-byte ID is unused in
DV-over-SDTI.)
470 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES