DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

IEC 61883-1, Consumer
audio/video equipment – Digital
interface – Part 1: General. See
also parts 2 through 5.
SMPTE RP 168, Definition of
Vertical Interval Switching Point
for Synchronous Video Switching.
to 800 Mb/s, 1.6 Gb/s, or 3.2 Gb/s. In addition, 1394B
specifies four additional media:
• Plastic optical fiber (POF), for distances of up to 50 m,
at data rates of either 100 or 200 Mb/s
• CAT 5 coaxial cable, for distances of up to 100 m, at
100 Mb/s
• Hard polymer-clad fiber (HPCF), for distances of up to
100 m, at 100 or 200 Mb/s
• Multimode glass optical fiber (GOF), for distances of up
to 100 m at 100, 200, 400, or 800 Mb/s, or 1.6 or
3.2 Gb/s
IEC has standardized the transmission of digital video
over IEEE 1394. Video is digitized according to
Rec. 601, then motion-JPEG coded (using the DV standard)
at about 25 Mb/s; this is colloquially known as
1394/DV25 (or DV25-over-1394). DV coding has been
adapted to 100 Mb/s for HDTV (DV100); a standard for
DV100-over-1394 has been adopted by IEC.
A standard for conveying an MPEG-2 transport stream
over IEEE 1394 has also been adopted by IEC; however,
commercial deployment of MPEG-2-over-1394 is slow,
mainly owing to concerns about copy protection. The
D-7 (DVCPRO50) and D-9 (Digital-S) videotape
recorders use DV coding at 50 Mb/s; a standard DV50
interface across IEEE 1394 is likely to be developed.
Switching and mixing
Switching or editing between video sources –
“cutting” – is done in the vertical interval, so that each
frame of the resulting video remains intact, without any
switching transients. When switching between two
signals in a hardware switcher, if the output signal is to
be made continuous across the instant of switching, the
input signals must be synchronous – the 0V instants of
both signals must match precisely in time. To prevent
switching transients from disturbing vertical sync
elements, switching is done somewhat later than 0V ;
see SMPTE RP 168.
134 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES