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Pulling video to bits
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28/11/2006
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Europeans are quite particular when it comes to watching video. More bits are used to encode a European high definition TV (HDTV) signal than the equivalent signal in the US. So says Arnaud Perrier, senior product line manager, high definition and advanced encoders at US video delivery firm Harmonic. “There is a difference in perception,” he says.
In the US, HD video is typically encoded at 9Mbit/s per channel; in Europe, it’s between 11 and 12Mbit/s. Perrier believes the difference stems from expectation set by years of watching Europe’s superior PAL tv format compared to the US’ NTSC standard. What such differences also highlight is the need for flexibility when encoding video.
HDTV has two formats: 720p, which uses 1280pixels x 720 lines with progressive scan; and 1080i, a 1920pixels x 1080 line format with interlaced scan. By contrast, standard definition tv is 704 pixel x 480 (NTSC) or 576 (PAL) lines, interlaced.
HDTV’s emergence coincides with an industry shift from Mpeg2 to the H.264/Mpeg4 Advanced Video Coding (AVC) standard. Whilst Mpeg2 is the mainstay approach to digital tv compression, AVC’s potential to halve the number of bits needed for comparable video quality means operators are keen to embrace the technology to make best use of scarce video delivery bandwidth.
“Every operator is interested in Mpeg4,” says Carl Furgusson, vice president of product management at Tandberg Television. However, the pace of AVC’s adoption differs between satellite, cable and telecom operators. Cable and satellite tv operators already have millions of Mpeg2 set top boxes (stbs) in the home. “Ten million [Mpeg2] boxes deployed becomes a $250million question as to when to move to Mpeg4,” says Furgusson. But telecom operators can go straight to AVC stbs now they have started rolling out IP based TV (IP TV) services over digital subscriber line (dsl).
Telcos also have the greatest need: they have the narrowest pipes of all – using up to 15Mbit/s ADSL2+ lines to the home. “The whole problem with telco DSL is bandwidth, especially with HD,” says Bob Larribeau, senior analyst at the Multimedia Research Group. ”With 8 to 12Mbit/s needed for HDTV and the rest for internet access, HD takes everything you’ve got.”
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Author
Roy Rubenstein
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