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									          PROGRAMMABLE PLATFORMS                                                                         INTER DESIGN


                                                                                                                         The move to HDTV is providing
                                                                                                                        opportunities for programmable
                                                                                                                       platforms. By Roy Rubenstein.




Pulling video to bits
E
       uropeans are quite particular when             mainstay approach to digital tv compres-             at the Multimedia Research Group.
       it comes to watching video. More               sion, AVC’s potential to halve the num-              ”With 8 to 12Mbit/s needed for HDTV
       bits are used to encode a European             ber of bits needed for comparable video              and the rest for internet access, HD takes
high definition TV (HDTV) signal than                 quality means operators are keen to                  everything you’ve got.”
the equivalent signal in the US. So says              embrace the technology to make best use                  The AVC standard builds on Mpeg2
Arnaud Perrier, senior product line man-              of scarce video delivery bandwidth.                  coding techniques. “The big driver for
ager, high definition and advanced                                                                         AVC was the issue of continually reduc-
encoders at US video delivery firm Har-               AVC versus Mpeg2                                     ing the bit rate,” says Furgusson. “At less
monic. “There is a difference in percep-              “Every operator is interested in Mpeg4,”             than 2.5Mbit/s, there is a rapid drop off
tion,” he says.                                       says Carl Furgusson, vice president of               in picture quality [with Mpeg2].”
   In the US, HD video is typically                   product management at Tandberg Televi-                   Several improvements are added to
encoded at 9Mbit/s per channel; in                    sion. However, the pace of AVC’s adop-               AVC to avoid such sharp degradation.
Europe, it’s between 11 and 12Mbit/s.                 tion differs between satellite, cable and            One is the standard’s syntax. “Perfor-
Perrier believes the difference stems from            telecom operators. Cable and satellite tv            mance drops off with Mpeg2 because
expectation set by years of watching                  operators already have millions of Mpeg2             there are more bits used on the syntax
Europe’s superior PAL tv format com-                  set top boxes (stbs) in the home. “Ten               than on video data [at sub 2.5Mbit/s bit
pared to the US’ NTSC standard. What                  million [Mpeg2] boxes deployed                       rates],” says Furgusson.
such differences also highlight is the need           becomes a $250million question as to                     Both coder standards use techniques
for flexibility when encoding video.                  when to move to Mpeg4,” says Furgus-                 such as pixel block prediction and a block
   HDTV has two formats: 720p, using                  son. But telecom operators can go                    based discrete cosine transform. Samples
1280pixels x 720 lines with progressive               straight to AVC stbs now that roll out of            are predicted with respect to the pixel
scan; and 1080i, a 1920pixels x 1080 line             IP based TV (IP TV) services over digital            block in the same video frame and with
format with interlaced scan. By contrast,             subscriber line (dsl) has begun.                     adjacent frames, known as motion com-
standard definition tv is 704 pixel x 480                 Telcos also have the greatest need:              pensation. It is the residual frame – the dif-
(NTSC) or 576 (PAL) lines, interlaced.                they have the narrowest pipes of all –               ference between the original input frame
   HDTV’s emergence coincides with                    using up to 15Mbit/s ADSL2+ lines to                 samples and the predicted block samples –
an industry shift from Mpeg2 to the                   the home. “The whole problem with                    that is discrete cosine transformed. The
H.264/Mpeg4 Advanced Video Coding                     telco DSL is bandwidth, especially with              prediction and quantised transform coeffi-
(AVC) standard. Whilst Mpeg2 is the                   HD,” says Bob Larribeau, senior analyst              cients are then packaged using a variable




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              PROGRAMMABLE PLATFORMS                                                                        INTER DESIGN


                                                         be limited regarding which tools to use for             40% improvement in coding efficiencies.
                                                         a given video – whether it’s a studio dis-                  Broadcasting video may drive coding
                                                         cussion with little movement or a rapid                 techniques, but it offers limited volumes
                                                         moving, wide scene change sports game.                  for chipmakers. “HD broadcasters could
                                                            Encoder specialists also use in house                use our media architecture, but it is a
                                                         video processing techniques prior to –                  niche market for us,” says Pete Hutton,
                                                         and independent of – the coding stan-                   senior vice president of engineering at
                                                         dard. For example, filtering techniques                 ARC International.
                                                         reduce noise and soften the image by                        ARC is more interested in higher vol-
                                                         removing sharp edges to ensure less resid-              ume video codec applications, such as
                                                         ual coefficients result.                                camcorders, handsets and stbs. It has
                                                            Other ways in which AVC improves                     recently launched its VRaptor media
                                                         compression quality at lower bit rates                  architecture that uses combinations of its
                                                         include in loop deblocking filtering to                 32bit ARC cores, 128bit single instruc-
                                                         remove noticeable block boundaries, and                 tion multiple data (SIMD) processors
                                                         entropy coding, which achieves between                  and hardwired engines for standard defi-
                                                         10 and 20% bit savings compared to                      nition and high definition coding appli-
                                                         Mpeg2’s bit encoding scheme.                            cations. For a high definition 1080i stb
     length coder – to reduce the bit stream fur-                                                                decoder design, it is developing a sub sys-
     ther – ready for decoding.                          Programmable platforms                                  tem that will likely use five ARC proces-
         The AVC standard is more efficient in           Broadcast video coding requires consid-                 sors and two or three SIMD accelerators.
     how the motion blocks and residual are              erable amounts of hardware. Harmonic’s                      Texas Instruments is also active, tar-
     encoded. For example, instead of 16 x 16            first generation AVC encoder uses 20                    geting both coding markets with its high
     pixel blocks, AVC uses a range of block             dsps. “We used an array of fpgas and                    end dsps and the DaVinci family of
     sizes, including 16 x 16, 8 x 16, 8 x 8 and         dsps, but were architecture limited in                  processors. Meanwhile, LSI Logic has
     4 x 4.” Smaller blocks are used where there         terms of inter chip communications,”                    just announced its Domino [X] proces-
     is more detail in the picture,” says Furgus-        says Perrier. That meant a picture needed               sor architecture. Bob Saffari, senior
     son. “And with smaller blocks, there is less        to be broken down into four or six slices,              director of marketing and business devel-
     residual data.” But there is a trade off            constraining the motion estimation                      opment for advanced video products at
     between bit rate efficiency and the greater         search area that could be performed.                    LSI Logic, says any chip architecture
     processing required by smaller blocks.                  “This year, there has been a significant            must be scalable to accommodate new
         This is where the coding expertise of           leap in the performance of HD encod-                    algorithmic developments. “For HD
     companies like Harmonic and Tandberg                ing,” says Perrier. The key is the addition             encoding, the architecture must be scal-
     counts. “AVC has many different process-            of asics in Harmonic’s latest encoder hard-             able enough to increase performance
     ing techniques, but it doesn’t tell you             ware. Harmonic can now compress an                      over time and enable new advance algo-
     which tool to use and when,” says Furgus-           entire frame at once, as well as use addi-              rithmic tools to produce superior video
     son. For real time coding, decisions must           tional AVC tools. The result is a 30 to                 quality at lower bit rates.”
                                                                                                                     Furgusson stresses that AVC is already
                                                                                                                 following the same development curve as
     Figure 1: ARC's VRaptor media architecture                                                                  Mpeg2. Tandberg has undertaken four
                                                                                                                 generations of Mpeg2 designs since it first
                  stream                      input filter                           scratch                     adopted the coding standard in 1994.
                   DMA                        extensions                            pad ram                          Perrier believes progress will continue
                                                                                                                 but, inevitably, will bring diminishing
                                                                                                                 returns. “Maybe there is an 20 to 25%
                                                                                                                 incremental improvement still to be
                 hardware                     ARC 750D                               media
                accelerator                      cpu                                processor                    gained,” he says.
                                                                                                                     Video coding challenges, however,
                                                                                                                 will continue. An extreme example is
                                                                                                                 UltraHD, the digital cinema standard
                  stream                     output filter                           media                       with a resolution of 7680x 4320 – 16
                   DMA                        extensions                             DMA                         times that of HDTV 1080i. UltraHD
                                                                                                                 will not be piped to your home any time
                                                                                                                 soon, but the trend is clear.




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