Component Video And IEEE 1394
Dear Gary It has recently come to my attention, through newsgroups on the Internet, that IEEE 1394 is being considered the “connection of choice” for high quality video transmission. Component has always been considered the best for video transmission, especially by video professionals in Hollywood post production work. Is component still the interface of choice for high quality video? Is IEEE 1394 considered better?
Jim Buchanan
Video Technical Editor Greg Rogers Comments:
The best video interface depends on what you need it to do, and who gets to choose. Component video interfaces can be analog or digital, RGB or YPbPr. We currently use analog component video interfaces to connect consumer video products such as DVD players and HDTV set-top boxes to displays. Professional video, used in broadcast and production facilities, uses digital YCbCr component video to interconnect products, such as cameras to digital tape recorders or video processors. Analog component video uses parallel interfaces—one cable for each component video signal, and up to two more cables for separate sync signals. Digital component video is typically transmitted over a serial digital interface (SDI). Digital component video data and equivalent sync information can be transmitted in a single SDI cable, but the serial data rates are extremely high. Standard-definition 10-bit SDI (SMPTE 259M) video is usually transmitted at a rate of 270 Mbps (megabits per second), and high-definition 10-bit HD-SDI (SMPTE 292M) video is about 1.5 Gbps (1500 Mbps). The cost of implementing HD-SDI video for consumer products is too high, and more importantly, no content protection exists for these standards. But for professional video applications, SDI and HD-SDI provide high quality, uncompressed component video. IEEE 1394, otherwise known as FireWire® by its inventor, Apple Computer (Sony calls it i.LINK), is a general-purpose serial bus that has been adapted for transmitting compressed digital video. It currently has a maximum serial data rate of about 400 Mbps, although faster versions of the standard are being developed (up to 3.2 Gbps). But for now it is primarily being touted for transmitting MPEG compressed video between devices such as satellite receivers and consumer digital video recorders. The cable TV industry had also adopted 1394 for connecting set-top boxes to high definition TVs. The key enabler for using IEEE 1394 is Digital Transmission Content Protection (DTCP), also known as “5C,” which refers to the companies that developed it. Just as we are going to press with this issue, a broad group of satellite and cable TV providers (including DirecTV and EchoStar’s DISH Network), consumer electronics manufacturers, and content providers, have agreed to use the Digital Visual Interface (DVI) standard for transmission from HDTV set-top boxes to displays, and high-bandwidth digital content protection (HDCP) for HDTV content. The DVI/HDCP standard uses four pairs of differential signals (digital RGB & clock) and has a maximum data rate of 4.95 Gbps, to deliver uncompressed high-definition video. We will have much more to say about the implications of this announcement in future issues. For more technical information read Alen Koebel’s article “Digital Video Interfaces And Consumer Displays” in Issue 47, April 2001.
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