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by Alan Hughes Digital TV and MPEG-4 The current state of play... The recent decision by the Nine Network to simulcast in MPEG-4 has caused consternation to a large number of TV viewers. This chaos is largely because TV sets were not required to be MPEG-4 compatible. So what is next? A t the start of last year, some 90% of TVs in use were capable of displaying the sharp images produced by full-HD broadcasts and Blu-ray discs. But virtually all TV broadcasts were in the much lower quality standard definition (SD), with the exception of some from One, SBSHD, 7Mate and GEM. Those exceptions are being broadcast with a degraded HD signal where the image is cut up into 1440 columns instead of 1920 columns, causing jagged edges in the image. The TV networks did this to increase the number of programs which can be broadcast from a single transmitter. Then, on 5th November 2015, the Nine Network, covering 60% of the Australian audience, started higher definition MPEG-4 broadcasting on channel 90, using 1920 columns, to provide much sharper pictures on their most popular programs. At the same time, Channel 9 continues to simulcast the 80  Silicon Chip same program in standard definition (SD). This means no viewer goes without Channel 9 programs, even if they cannot receive channel 90. Fitting a new high definition signal into existing transmissions did present a major problem for the Nine Network. The easiest change would have been to replace 9GEM with 9HD programs but an additional 33% data capacity would have been required and this would not fit into their existing transmission channel. This is where MPEG-4 Advanced Video Coding, otherwise known H.264, came to the rescue. It requires 50% less bandwidth than MPEG-2 for equivalent video quality. Nine decided to use MPEG-4 to reduce the 9HD data rate to accommodate the 33% increase and it still leaves enough capacity to transmit 9GEM in standard definition. MPEG-4 AVC was already being used when Nine started 9HD. Racing.com started using H.264 on the Seven Netsiliconchip.com.au work’s channel 78 and the Prime7/GWN7 networks started on 29th August 2015. 4Me (channel 74/64) is now broadcasting with MPEG-4 while NBN, WINHD and the Ten Network started in March this year. Note that all existing HD channels still use AC3 audio encoding, at about 480kbit/s, which occupies a fairly significant proportion of the bandwidth. Sound is much more efficiently compressed by Advanced Audio Coding (AAC) which is being used for Racing.com, 4ME and 7Flix at around 70kbit/s. Many sets will not decode MPEG-4 signals and so will produce a blank (usually blue) screen and perhaps a message. No one actually knows what proportion of TVs will receive MPEG-4 signals. The Australian Communications and Media Authority has been advised that 80% of receivers are MPEG-4 capable but they provided no reference for this statistic. All of the set-top boxes provided free to pensioners are MPEG-4 capable. Sony has publicly stated that all their TVs sold from 2009 are MPEG-4 capable. Typically, TV manufacturers’ specification tables do not mention what compression methods they will accept. All Freeview products released since 2009 are MPEG4 capable. In the meantime, if you have set which is not MPEG-4 compatible, you will need a set-top box which can do the job. Make sure of that aspect before you buy. When a sufficient proportion of receivers are MPEG-4 capable, Channels 2, 3, 5, 6, 7, 8, 9, 10 should become FHD and 30, 80, 90, 13 and other yet to be specified change to SD at a low data rate like that used by 4ME. Along with this change, all secondary programs should be MPEG-4 compressed enabling allowing One, 7Mate, 9GEM to return to FHD alongside the primary program. This will maximise the viewing of the sharper pictures. Why was this chaos allowed to happen? All commercially produced Blu-ray discs use full high definition which includes progressive scan to minimise jagged edges, particularly on curves and diagonal detail in the pictures. Look at the lines on a tennis court during tennis telecasts. Progressive scanning also causes a reduction of the data rate in complex moving pictures. TV technology has changed since the picture tube TV was retired. Typical flat screen TVs show each frame up to eight times (at 200Hz), modifying each repeated frame to provide smooth motion display. Modern TV & video cameras are all digital now and so are natively progressive scan. There is no longer any reason to broadcast interlaced content. Older shows recorded on video tape, can be converted to progressive scan. It is up to the broadcasters to utilise progressive scanning in all equipment including compressors, so as to match the quality of Blu-ray discs. Ultra-high definition 4K TV signals (as used in cinemas) and computer screens are all progressively scanned. Pixellation problems HD/SD simulcast can cause pixellation and other artefacts, particularly during sporting broadcasts. This is because they use statistical multiplexing to maximise the number of program channels they can transmit. A TV channel can carry 23Mbit/s, of which a statistical multiplexer allocates a portion to each program stream. More of the data is allocated to images containing more detail and motion than static images of little detail. But unfortunately, an HD/SD simulcast has a pair of channels where the greatest demand occurs at the same time, because the images are similar and therefore the bandwidth available to each channel is insufficcient to provide the required image detail. As a result, simulcasting should be terminated as soon as possible. MPEG-4 is not new; far from it. The MPEG-4 version 10 compression standard was approved for worldwide use in 2005 and New Zealand has used MPEG-4 for all of their TV broadcasts. In Australia, we have had digital TV since 2001 but using the less efficient MPEG-2 compression. The root of the chaos lies in Australian Standard AS 4933.1-2010 Digital television - Requirements for receivers – VHF/UHF DVB-T television broadcasts. This standard made MPEG-4 reception optional, saying that broadcasters may use it and so importers and retailers do not have to comply. If the standard had made MPEG-4 compulsory back in 2010, nearly all TVs, personal video recorders and set top boxes would now be able to receive MPEG-4 signals. As recently as January 2015, the Department of Communications asked for submissions to a “Digital TV Regulation” enquiry. Every broadcaster rejected MPEG-4, preferring to wait for Ultra High Definition, but none of them suggested any concrete plans on how to achieve it. Right now, every broadcaster could transmit two or three of their programs in full high definition using MPEG-4 video with progressive scan, accompanied by HE AAC V2 sound. The chaos will continue Progressive scan Preventing the recurrence of chaos All of the AS4933 versions of the standard specify that all HD TVs must be able to display film mode, now called “full high definition” by TV manufacturers and retailers. All TV receivers which are not compliant with the current version of AS4933.1 should immediately be banned from importation and sale, to protect the public. siliconchip.com.au Since MPEG-4 was standardised, television technology has improved its efficiency through the standardisation of DVB-T2 and HEVC (H.265). DVB-T2 increases the data capacity of an “over the air” TV transmission channel by 44% compared to H.264. It is now in use in 37 countries, including the UK and all of Russia. High Efficiency Video Coding (HEVC) halves the data rate for MPEG-4 and is currently required for watching Netflix in UHD. Germany has been broadcasting UHD test signals in Berlin for a year at medium power. The USA broadcasters are now pushing for ATSC 3.0 using a version of DVB-T2 and HEVC to be rolled out as part of their digital repack. We did a similar restack, which was completed in 2014. AS4933.1-2015 Digital television - Requirements for receivers - VHF/UHF DVB-T television broadcasts make no mention of the Australian use of DVB-T2 or HEVC and was published six months after the DTV regulation inquiry. Hence consumers are not being informed how to “futureproof” their TV purchases, particularly when so few TVs currently available are future-proofed. April 2016  81 ANTENNA DVB-T2/T TUNER AND DEMULTIPLEXER CHANNEL SELECTOR HEVC/MPEG-4/ MPEG-2 VIDEO DECOMPRESSOR UPSCALER xHE-AAC V2/AAC/ AC3/MP2/MP1 SOUND DECOMPRESSOR SOUND DIGITAL TO ANALOG CONVERTER 384 x 2160 x 120p DISPLAY IMAGE MEMORY >16MB 5.1 SURROUND SOUND SYSTEM INTERNET HDMI INPUT A functional block diagram of a “Futureproofed TV” containing over-the-air reception, hybrid broadcast broadband for catch-up TV and the use of external devices. AS 4933.1-20## Digital television - Requirements for receivers - VHF/UHF Terrestrial television broadcasts needs to have the compulsory requirement for DVB-T2 and H.265 support added. ACMA, through the Customs Act, has the power to make it compulsory and should do so. Currently all Sony, some Panasonic and some Samsung TVs are DVB-T2 capable. Hisense is the only manufacturer to state in their specification that their UHD TVs are H.265 or HEVC capable; unfortunately, they are not able to receive and decode DVB-T2. Many manufacturers do not quote the type of compression and modulation they will receive in their specifications. MPEG-4, HE AAC V2 sound, HEVC and DVB-T2 technologies are not backwards-compatible. The inclusion of the newer technologies makes little difference to the price of new receivers, when employed in very large numbers. However manufacturers must specify which types of signal they can receive. Future options If all broadcasters convert to DVB-T2 modulation and HEVC compression on each program regardless of the definition, then each broadcaster will be able to transmit a main program in ultra-high definition and still transmit their existing secondary channels. If this occurs within seven years’ time it will give viewers time to replace their TV sets and also for broadcasters to upgrade the modulator in every transmitter in Australia. Netflix requires a stable download speed of 25Mbit/s for UHD programs and many people who are yet to get the NBN will never be able to achieve this speed. To get the signal to the viewer, the price is fixed using broadcasting, whereas when broadband is used the price rises as the number of simultaneous viewers increase. It would appear that all other broadcasters will expand their use of MPEG-4 compression this year. A major chain store is still selling MPEG-4 capable HD set top boxes for under $30. Connect it to a digital TV using an HDMI cable to be able to see available programs with the sharpest images possible. Free TV Australia, ABC, SBS, the Department of Communications, ACMA, importers and Choice should include DVB-T2, HEVC and HE AAC V2 sound in an updated AS4933 to speed the introduction of ultra-high definition 82  Silicon Chip TV from all broadcasters and to protect the investment by viewers. Future-proofing TVs A DVB-T2 tuner is capable of receiving signals containing 40% more data for the same bandwidth as MPEG-4 AVC. The channel selector which is controlled by the remote control, selects the transmission channel and the selected program within that channel. The decompressors are fed with either the off-air or catchup/streamed programs, which both need their pictures and sound decompressed. The HDMI input is used for Blu-ray players etc, which supply uncompressed digital signals. The video is then up-scaled unless it is ultra-high definition already. Then the image is stored, decoded into red, green and blue signals for display. The image memory is read in sequential order and fed to each pixel in the display in turn. Off-air and internet sound has to be decompressed and then converted to analog for amplification and feeding to speakers. Up-scaling is magnification Ultra-High Definition images have the highest number of picture elements; lower definition images contain fewer pixels. The diagram overleaf shows the image sizes for all types of signals from commercial cinema at 4096 x 2160 (ie, 4K) down to American SD TV at 720 x 480 pixels. The thick line shows the edge of the screen. A true UHD signal will fill the screen. Since 4K movies have slightly more columns than UHD TV (4096 vs 3840), this results in 3.5% cropping on the left of the screen and another 3.5% on the right. Poorer resolution images contain fewer pixels and hence would only cover part of the screen if shown pixel for pixel. Viewers tend to like images which fit the full screen. To achieve this, the manufacturers have to magnify the lower resolution images. Magnification or up-scaling is achieved by interpolating adjacent picture elements. Picture elements or Pixels A pixel is the smallest area in an image which can change colour. If you graph the output of a camera which is panned across a star, you will get the voltage output shown below, siliconchip.com.au Horizontal Resolution # Incoming # incoming # outgoing Magnification pixels/line sample sample by area to display Ultra-high definition Full high definition Aust HD ABC24 (720p) SD World SD America Racing.com 4ME Vertical Resolution UHD FHD Aust HD ABC24 SD World SD America Racing.com 4ME 3840 1920 1440 1280 720 720 640 528 1 1 3 1 3 3 1 11 1 2 8 3 16 16 6 80 1 4 5 9 20 24 23 27 # Incoming # Incoming # outgoing lines/frame sample sample to display 2160 1 1 1080 1 2 1080 1 2 720 1 3 576 4 15 480 2 9 576 4 15 576 4 15 The number of pixels per line and lines per image for common TV broadcast resolutions. as the lens will make the star appear circular; the higher the definition, the smaller pixel diameter. The objective is to recreate the pixel size on the UHD screen which matches that of the lower resolution image original. UHD cameras provide the sharpest images for UHD displays. Up-scaling does not usually increase the sharpness of lower resolution images; this would require a sophisticated algorithm which would generate detail which was not recorded in the original video. Such algorithms do exist (see http://www.cs.huji.ac.il/~raananf/projects/lss_upscale/ sup_images/) but this requires significant processing power and most TVs do not have this capability yet. High Frame Rate TV (HFR) Commercial Blu-ray discs are recorded at 24 frames per second which is the standard moving picture film speed. With the exception of the Americas and parts of Asia, progressive scan TV has a frame rate of 25 frames per second. New UHD/4K programs can have a frame rate from 24-120fps, however broadcast TV and Internet streaming video will probably be limited to 60fps. At the moment, there are no broadcasts at these frame rates. Higher frame rates create very smooth movement in the image. As noted above, current 200Hz TVs show each frame eight times. The better TVs calculate the vectors of movement and modify the repeated frames to smooth the illusion of motion which removes jerky movement. But high frame rate signals give more natural results. High Dynamic Range TV (HDR) Current displays are capable of much better contrast ratios than the old fashioned cathode ray picture tubes (CRTs). Currently, most displays have a pixel colour depth of 8 bits each for red, green and blue, giving 256 brightness levels (28) . To take full advantage of the high contrast ratio of newer displays, HDR programs will use 10 bits per luminance sample, giving 1024 brightness levels (210). This increases the maximum possible contrast ratio by four times, to over 1000:1. Wider range of colours It’s also possible for modern displays to have an extended colour gamut. Greens and reds can be much more saturated, along with the ability to prouce longer red photon wavelengths. 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See article previews at www.siliconchip.com.au ORDER NOW AT The brightness level output of a single-pixel image sensor as it passes over a pixel-sized bright object such as a star. siliconchip.com.au www.siliconchip.com.au/shop April 2016  83 Graphical representation of the various definition standards currently in use. Australia and New Zealand SD is the grey area, top left of diagram. Compare this to Ultra High Definition (yellow) – in fact, there is no comparison! capture a wider range of colours and laser/OLED displays can display them. Hybrid Broadcast Broadband TV This system is being used by broadcasters for catch-up TV, as shown in the Freeview advertisements. HbbTV 2.0 is the next upgrade from FreeviewPlus. It will require HEVC/HE AAC v2 (with 5.1 surround sound) compression to minimise data rates for everything from phones to UHD TV. Receivers will be able to store programs for Video On Demand. Worldwide digital TV standards North America and South Korea transmit ATSC which uses MPEG-2 compression and a poorly performing, essentially serial data transmission system. They have developed ATSC 3.0 which is similar to DVB-T2 and will use HEVC compression and they are pushing for its adoption. Japan, parts of South America, Philippines, Sri Lanka and Botswana use ISDB-T which is similar to DVB-T2, including MPEG-4 or MPEG-2 compression. DVB-T2/MPEG-4 is already in use in 37 countries including the UK’s HD programming, and Igloo pay TV in NZ. It has been adopted by 73 countries. The balance of the world is using DVB-T. 84  Silicon Chip For those with poor hearing and eyesight All digital TVs are capable of displaying sub-titles for those with difficulty hearing. The Closed Captions are coloured according to who is speaking and also describe off-screen sounds. Until the end of June this year there is a trial of Audio Description on ABC iview for those with poor eyesight. The scene is described during gaps in the dialog. http://iview. abc.net.au/programs/audio-description-a-new-feature-oniview/IV1462H001S00 The series of Advanced Audio Compression standards specifies that an Audio Description channel is available and the sound is mixed with the main sound in the receiver, when selected by a button on the remote control. In the UK 10% of all programs are broadcast with Audio Description. For the future From now on all TVs need to support DVB-T2/T, HEVC/ MPEG-4/MPEG-2 video and MPEG-1/AC3/HE-AAC sound. Upscaling support will be required for lower resolution content. Once the integrated circuits for the above functions are designed and manufactured for a worldwide market, the increase in TV cost should be very small. Note: as this article was going to press, TEN, NBN and WIN began Full HD broadcasting with MPEG-4 AVC. SC siliconchip.com.au