ATSC A/65C, Program and System Information Protocol for Terrestrial Broadcast and Cable with
Amendment 1, May 9, 2006AV/C Commands for the Management of Asynchronous Serial Bus Connections, Version 1.1,
1394 Trade Association Document 2000006, October
被代替标准
EIA-775-ACEA-775-ACEA-775-B
适用范围
CEA-775-C defines mechanisms to allow a source of MPEG service, such as a cable or terrestrial set-top
box, digital VCR, or DTV to utilize the MPEG decoding and display capabilities in a DTV. A method is included to allow the OSD Producer to supply bitmap graphic overlays for blending and composition in the DTV over decoded video.
CEA-775-C supports an optional baseband analog audio/video connection between an audio/video
source device and the DTV. Mechanisms are provided to allow the source device to control the selection
of the audio/video source for display in the DTV between an MPEG service decoded in the DTV and
incoming analog audio/video supplied to it via an external input.
Nothing in CEA-775-C is intended to constrain the use of other 1394-based protocols.
1.1 Background
The currently implemented analog audio/video home entertainment cluster consists of various signal
sources and various display devices. Possible audio/video sources in this system include a video
cassette recorder, a DVD player, and a DBS or cable set top box. In the analog system the audio/video
source can overlay its graphical user interface on its output video as shown in Figure 1. This allows the user to control the source based on information shown on the TV display.
A Digital Television (DTV) system using a similar model is not currently practical. Figure 2 shows an
example of what would be required. The process of decoding the original bitstream to include the GUI
overlay and then re-encoding for transmission to the DTV adds significant complexity and usually
degrades picture quality.
CEA-775-C defines a specification for a compressed audio/video digital interface to a DTV that provides a
level of functionality that is similar to an analog audio/video system or an uncompressed digital
audio/video system (e.g. HDMI). A representation of a typical system is shown in Figure 3. This diagram
shows an A/V Source that is capable of producing analog audio and video and also compressed audio
and video delivered as an MPEG Transport Stream. The analog signal is transmitted over a standard
coaxial cable and the MPEG Transport Stream is passed over an IEEE 1394 bus. Bitmaps of the source
OSD are sent separately over the same IEEE 1394 bus and are mixed with the decoded MPEG video in
the DTV prior to being presented on the display. This process removes the need for the A/V Source to
perform the additional MPEG video decodes and re-encodes. The IEEE 1394 bus is also used by the
source and display to exchange control and status messages.
The digital interface is based on the IEEE 1394 Standard for a High Performance Serial Bus [16], the IEC 61883-1 digital interface standard [10], and on the AV/C Digital Interface Command Set General
Specification [6]. The IEEE 1394 Standard originated in Apple Computer as a multi-media interconnect.
The standard provides:
a) Data transmission at various data rates. CEA-775-C requires support for the s200 or higher level of
service defined in IEEE 1394-1995 (s200 has a bit rate of 196.608 megabits per second).
b) Inexpensive and physically small interconnection
c) Hot pluggable connection
d) Daisy chained or branched interconnection
e) Guaranteed bandwidth for isochronous data
CEA-775-C is designed to enable interoperability between a DTV compliant with CEA-775-C and various
types of Consumer digital audio/video sources including digital set-top boxes (STBs) and analog/digital
hard disk or videocassette recorders (VCRs). CEA-775-C defines a level of functionality that allows
compliant systems to:
a) Discover and adapt to OSD functionality supported in the display device
b) Pass an MPEG-2 Transport Stream from the bitstream source to the display device
c) Transmit OSD information from the OSD Producer to the display device or OSD Consumer
d) Control the selection of different sources to the display device