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Designing a progressive scan DVD player and advanced set-top box

Posted: 20 Mar 2000 ?? ?Print Version ?Bookmark and Share

Keywords:sigma designs? dvd? hdtv? mpeg? ntsc?


International IC ? China ? Conference Proceedings 207 True progressive video decoders can deliver full quality from DVD and MPEG sources on Digital and HDTV monitors. The launch of DVD has been heralded as one of the most suc- cessful consumer product launches in history. Over 6 million players have been sold, and two titles - Titanic and The Matrix -- have already sold in excess of one million copies. DVD is expected to continue on an explosive growth path for many years to come. As HDTV broadcasts begin over the next few years, sales of newer television sets - combinations of HDTV, digital, progressive (non-interlaced), andWidescreen- will also increase worldwide. DVD technology must also adopt, and support higher quality than NTSC and PAL. Otherwise, consumers will prefer to watch the HDTV broadcasts on their HDTV sets, which will threaten the billion-dollar movie sales/rental business. Fortunately,DVDwasdesignedtowithstandthisthreat.Infact, the video quality and resolution oftoday's DVD titles significantly exceeds the capabilities of ordinary televisions. In theYear 2000, new televisions and DVD players will emerge which take advan- tage of the advanced capabilities found in today's titles. DVD encompasses more than 20 years of improvements in audio/visual research and technology. The results are absolutely stunning. In Appendix A, you will find a review of many of the aspects of the DVD Video format which produce superior video quality.Becauseofitsdigitalvideotechnology,wideranalogband- width, component video format, and its anamorphic, Widescreen aspect ratio, DVD titles produce remarkably better video quality on standard and Widescreen television sets. There is one additional area where a well-engineered DVD player can make a tremendous difference, and that is for Progres- sive DVDVideo playback. Sadly, virtually allTV transmissions in the world are interlaced.The interlaced format introduces massive amounts of noise and distortion into TV images, and removes the "film-like" quality of images. Any rapidly moving object has its resolution cut in half, and visible, jagged lines of noise border vir- tually everything that moves, especially diagonal lines. It can be argued that the vastly sharper image quality of DVD's make this last artifact all the more obvious to consumers. The improvement gain from Progressive DVD playback tech- nology can easily be expressed as a doubling of resolution, and this figure is correct when it refers to playback on a progressive, non-interlaced display. Plus, an additional 33% resolution is made Designing a progressive scan DVD player and advanced set-top box Bill Wong Vice President of Marketing Sigma Designs, Inc. available in Widescreen mode. The elimination of interlace artifacts brought about by Progressive DVD technology has far moreimpactthanmerelydoublingtheresolution.ProgressiveDVD offers a dramatic leap in image quality, one that makes DVD playback on a large, progressive television a true alternative to a movie theater. Progressive DVDtechnology works for two reasons: First, vir- tually all DVD's are made from film, not from a video camera. A movie camera captures an image all at once onto a piece of film, and it does this 24 times each second (24 fps).A video camera, by comparison, captures every other line of an image at a rate of 60 fields per second. In order to convert any 24 frame/second film intothe30frame/secondworldofNTSCTV,6framesofthemovie are duplicated in each second (seeAppendix B). This is why Progressive DVD technology works: In creating the DVD standard, the inventors realized that saving the most pos- sible space on the 4.7 GB DVD disc was essential. One way to savespace,theydecided,wastoavoidputtingtheduplicatedframes of video on the disc. Not putting the duplicated frames on the disc results in a savings of 20 percent. Because of this, virtually every DVDthatyoubuycontains24framespersecondofvideo,whether it is intended for NTSC or PAL playback. The DVD players sim- ply reads certain codes in the DVD's MPEG stream to figure out which fields to duplicate, so it is the DVD player itself which per- forms the 3:2 Pull Down operation. Because of these design features in DVD, it is possible for a properly designed DVD player to display not a 720 x 240 pixel field, but a complete 720 x 480 pixel frame, all at once.When used with a non-interlaced display, such as an HDTV, projector orVGA monitor, the result is twice the resolution and an elimination of the awful-lookinginterlaceartifactswhichhaveplaguedbroadcasttele- vision since the 1950's. Currently, high-definition television (HDTV) trials are underway throughout the United States and elsewhere, which is causing an explosion in HDTV sales.As more and more consum- ers purchase these sets, demand for HDTV-compatible DVD play- ers will skyrocket. The "attach rate" of Progressive DVD player sales to HDTV sets may well be close to 90 percent, and it will signal the end of VHS tape technology. Anyone designing or developing a DVD player for sale in the Year 2000 should consider Progressive DVD playback to be a 208 International IC ? China ? Conference Proceedings "check-list" feature. By the time the Christmas 2000 selling sea- son begins, every high-performance DVD player will have pro- gressive output, and a year after that, it will probably be impos- sibletopurchaseaDVDplayerwithoutProgressiveDVDsupport. Of course, the standard interlaced connections will remain, but Progressive DVD will quickly become a requirement, just like the Dolby Digital S/PDIF connector. Adding Progressive DVD capability to a DVD player design starts with the right decoder silicon. The REALmagic EM 8400 MPEG-2/DVD decoder chip has several key features that make it ideally suited for both progressive and interlaced operation: ? Full-frame, progressive decoding ? Intelligent, microcode-based processing of frame-based content ? Letterboxing of Widescreen content ? Hardware audio/video synchronization with frame rate con- version ? High performance, 8-tap scalar ? Embedded DVD navigation software ? Support for RGB and YUV (Y Pb Pr) outputs ? Full-screen, 256 color OSD with alpha blending Below is a block diagram of the EM 8400 chip: Functional description The RISC core of the EM8400 contains a 66 MIPS proprietary RISC processor. The RISC performs most control tasks for the EM8400, and video decoding down to the block level. DVD audio and video decryption is also built-in. The following host interfaces are supported: PCI 2.1, VMI A, VMI B, VIP 1.1 and VIP 2.0. Simple glue logic can be used to adopt other inter- faces, if needed. EM8400 includes a DRAM controller which supports 2 MB ofSDRAMor2/4MBofEDO.Using4MBenablestheon-screen display controller to support the full resolution of 720x525 pixels at 8 bits/pixel, with 4-bit alpha blending. The MPEG engine of the EM8400 contains four MPEG de- coding modules: Huffman decoder, inverse quantizer, IDCT and motion compensation. The audio engine contains blocks: audio sync, AC-3/MPEG audio decoding, PCM, and serial output. This supports the following audio formats: Dolby Digital (AC-3), ISO11172-3 MPEG layers 1 and 2, and non-compressed linear PCM, output via the stereo audio DAC and SPDIF encoder. DTS digital audio output over SPDIF is also supported. The audio synchronization engine can synchronize the video output to slave to the audio, by duplicating the closest video frame. In this way, a 24 or 30 frame/sec MPEG stream can be output to a display with nearly any refresh rate, from 25 up to 120 Hz. The on-screen display (OSD) controller supports DVD menus andsub-pictures,andcanindependentlysupportfull-screengraph- ics. The OSD can be used to provide a detailed menu system for player set-up, user feedback, and other interactive features. For example,atranslucentgraphiccanappearon-screenindicatingthat the user has pressed the "Pause" button. Large televisions typically have only one or two ideal resolu- tions.Ahigh-qualityProgressiveDVDplayermustbeabletomatch the ideal resolution, aspect ratio, frame rate and color space (RGB/ YUV) of the TV it is attached to. For example, an HDTV may have an optimal resolution of 1280 x 720 at 72 Hz andYUV input, while a projector might require RGB input of 1024 x 768 resolu- tion at 60 Hz. The EM 8400 is designed from the ground up to support this versatility, and produce properly formatted and syn- chronized video on virtually any type of progressive display. DVD player design Here is an example block diagram, which shows how an EM 8400 could be implemented into a high-performance DVD player with both interlaced and progressive outputs: In this DVD player, an inexpensive, integrated host processor performs disk i/o, manages IR input, and executes the EM 8400 driver.CompletedriversoftwarefortheWindRiverVxWorksRTOS and QNX are available from Sigma Designs. Because both the driverandtheEM8400microcodeareupgradeable,makingmodi- fications such as localizations or GUI customizations for OEM's is very simple to do. Because Sigma Designs can supply the navigation and driver software with the EM 8400, this design can be brought to market very rapidly. The advanced OSD capabilities of the EM 8400 enable a much richer, more interactive DVD playback product, which is easier and more fun to use than other DVD players. On- screen menus can be used to control all DVD playback features, offer instruction in the player's use, and manage player set up. The progressive output of this design is brought out on the YUV 8/16 line. The frequency and line rate of this output can be programmed by the EM 8400, and it can be transmitted to the Sigma Designs EM 9011 Analog Encoder. This inexpensive de- vice can format the CCIR 601YUV (Y Cb Cr) into eitherY Pb Pr or RGB analog progressive video.An NTSC/PAL encoder built-in to the EM 8400 handles standard, interlaced Composite and S-Video output. Automotive DVD design Another new area for DVD playback is inside automobiles. Advanced new automotive entertainment systems, what Intel calls in-car computing, efficiently combine a vast array of tech- nologies into a comprehensive entertainment and driving plat- form which replaces the typical car stereo. Offering a combina- tion of features, such as a CD and DVD changer, GPS naviga- tion, cell phone, Dolby Digital surround sound, and DVD play- back, this voice-activated technology has the potential to be- come a standard feature on most new cards sold in the 21st International IC ? China ? Conference Proceedings 209 century. Because DVD playback needs to run concurrently with other applications, such as satellite navigation and cell phone operation, hardware accelerated playback is essential. In the case of in-car DVD playback, the specification typically requires that the video playback be in the rear seats only, to avoid distractingthedriver.Theaudiocanbeplayedeitherthroughahead- phonejack,orbyusingthecar'sspeakersystemfortrue5.1channel Dolby Digital audio. The DVD changer serves double-duty as stor- age for the map data required by the GPS navigation software. Sigma Designs has worked closely with Microsoft and Intel to create a reference platform for in-car computing, and the Sigma Designs EM 8220 DVD decoder is designed as either a built-in chip or as an add-in module. The block diagram is below: The AutoPC DVD Expansion Module is a simple design to implement into the Intel/MicrosoftAutoPC, in-car computing en- vironment, and makes extensive use of power management and low current design. This design was created in close collaboration with Intel, Microsoft and Clarion, and is an excellent example of the flexibility of the EM 8400 design. In this design, the standard EM 9010 or NTSC/PAL TV encoder output was substituted with an LCD controller capable of reading the CCIR 601 output of the EM 8400. This device directly drives the back-seat LCD display. Simultaneous, dual audio outputs support both stereo headphones as well as Dolby Digital output to the car audio amplifier. TheEM8400hasbeenusedinmoreadvanceddesignsaswell,such as interactive set-top boxes which can surf the web, play DVD's, watch digital satellite TV and view MPEG-2 broadcast and on-demand over ADSL or switched Ethernet. This flexibility, as well as comprehensive device drivers, licensed DVD navigation software and high quality, Pro- gressiveDVDoutputmaketheEM8400anoptimalchoiceforadvanced digitalvideodesigns. Appendix A Some engineers may wonder this: If a traditional television broadcast is analog, how can DVD produce better results, con- sidering the fact that the MPEG-2 digital video compression method is known to be lossy? After all, MPEG-2 obtains com- pression of between 50:1 and 100:1 on DVD's by throwing away a tremendous amount of information, and "approximating" that information on playback.Analog video doesn't throw away 99% of the data, so the image should be better... right? Wrong. The fact is that TV broadcasting does implement a form of analog signal compression which degrades image quality substantially. Analog video compression is obtained by under-sampling the color information of a video signal. In a computer display, an im- age is composed of three elements: the Red, Green and Blue signals. These three signals are swept across the monitor for each line on the screen, drawing a complete picture from top to bottom. A television signal, however, is comprised of three different visual elements: Luminance, which is the signal which displays a com- plete image on black and white sets, Red Chroma, which is the difference between the red signal and its Luminance, and Blue Chroma,whichisthebluesignalminustheLuminance.TVbroad- casters under-sample both Chroma values, and this works because the human eye is more perceptive of Luminance differences (or the contrast between objects) than Chroma (color) differences. While the Luma signal is sampled for each pixel, the Chroma in- formation is sampled for approximately every four pixels. Compounding the problem of under-sampled color is that of modulation. InTV transmissions, the two color channels are modu- lated onto the Luma signal.This modulated, composite video signal is also used in the VHS and Laserdisc video formats. Recently, ad- vanced "comb filtering" devices have made their way into mid- and high-endtelevisionsets,andthesefiltersimprovetheprocesscleanly of separating the color information away from the Luma. Yet, no matterhowextensivethevideoprocessing,oncetheChromasignals aremodulatedontotheLuma,imagequalitysuffersbadly.Themost visible result of this is called Chroma crawl, which is seen as patters of dots "crawling" around sharp object borders. This noise affects overall image quality severely. DVD's are mastered and decoded into three separate video components. In the digital format, these components are namedY (Luminance), Cr (Red Chroma), and Cb (Blue Chroma).Virtually allDVDplayerssoldtodayfeatureoutputconnectorsforbothcom- posite (multiplexed Luma/Chroma) and S-Video (Separate Luma with the two Chroma channels modulated together).Although the results of modulating the two color channels independently of the Lumadrasticallyimprovescolorquality,foroptimalquality,agood DVD player should output all three components separately. This type of video connection is also analog, and is a translation of the digitalY Cb Cr format into the analogY Pb Pr format. Because DVD's do not modulate the Luma and Chroma signals together, and because the DVD signal is sampled at a higher rate than broadcast TV, and because of the wider, 6 MHz bandwidth of a DVD's output, a better quality image can be produced by a well-designed DVD player. But there is even more which a well-designed DVD player can do to widen the differences between broadcast TV and DVD video quality. For one thing, TV broadcasts assume that conventional TV sets over-scan the images they display. The majority of DVD's produced today are made in the anamorphic Widescreen for- mat. This format uses ordinarily unused scan lines to produce a wider image, with 33% more resolution. However, this ad- ditional resolution can only be viewed on a progressive and/ or Widescreen TV capable of supporting the format. A prop- erly designed DVD player must be able to support standard, or "4:3" TV's, as well as Widescreen, "16:9" televisions. When playing a Widescreen titles on a standard, 4:3 TV set, the DVD player must vertically scale the image -- with the best pos- sible quality - and display black, "letterbox" bars above and below the image. In Europe, Widescreen TV sets are currently very popular. These sets accept a standard, interlaced PAL video signal, but can take advantage of Widescreen DVD movies. However, it should be noted that most European TV's do not have componentY Pr Pb connectors, and many do not even have S-Video inputs. Instead, a format called Scart is used. Scart connectors carry both audio and video input and output, so connecting a VCR is accomplished by 210 International IC ? China ? Conference Proceedings Presentation Materials attaching just one cable. Scart video can carry either a composite or a component RGB video signal.Without Scart-compliant RGB output, it is difficult to sell a high-quality DVD player to Europeans. These issues must be addressed in the design of any high-qual- ity DVD player. The EM 8400 decoder has support for all of these capabilities in hardware. Appendix B Because the NTSC TV format used in much of the world has a rate of 29.97 interlaced frames per second, it is necessary to convert the frame rate of film into the frame rate of video. In this process, 6 frames of video must be duplicated in each sec- ond, and these 6 frames are evenly distributed throughout each second of video as 12 additional video fields. A frame of video has a resolution of 720x480 pixels, while a field has a resolu- tion of 720x240. Two fields are displayed sequentially on an interlaced TV set to create one frame. Intypicalfilm-to-NTSCvideoframerateconversion,everyother frame of video has one of its fields duplicated during playback, in a repeating pattern of 3-2-3-2 fields per frame.This pattern,known as 3:2 pull down, is used whenever a 24 frame per second film must be displayed on an NTSC television, such as the broadcast of a movie, or during the creation of aVHS tape, DVD, or Laserdisc. In VHS, the additional fields are recorded onto the tape. On a DVD,however,theadditionalfieldsarenotrecordedontotheDVD. Instead, the 24 frames of MPEG video on the DVD contains in- structions telling the DVD player which fields it should duplicate, and the result is a disc storage savings of about 20%. Because of this design feature of MPEG-2 and DVD, most DVD's are manufactured at a resolution known as 480p, even though most consumers believe that their DVD's are 480i. Author's contact details Bill Wong Sigma Designs, Inc. 355 Fairview Way, Milpitas, CA 95035-3024 USA Phone: 1 408 957 9850 Fax: 1 408 957 9791 E-mail: International IC ? China ? Conference Proceedings 211 212 International IC ? China ? Conference Proceedings International IC ? China ? Conference Proceedings 213 214 International IC ? China ? Conference Proceedings International IC ? China ? Conference Proceedings 215 216 International IC ? China ? Conference Proceedings

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