ADVANCED CODING FURTHERS HD SERVICES

Carl Furgusson TANDBERG

Abstract have reduced the bit rate required to digitize an acceptable broadcast quality picture into the The use of to home. Figure 1 shows this bit rate reduction enable bandwidth efficient HDTV Video on over time for MPEG-2. Demand and broadcast television is gaining in popularity as technological advancements in MPEG-2 compression continue to slow. While First Broadcast MPEG-2 has been the undisputed leader in 8 MPEG-2 Encoder video compression for the past decade, 7 Statistical algorithms such as Windows Media 9 Video B Multiplexer i 6 Enhancements and MPEG-4 Part 10 are emerging at a time t 5 Enhanced Motion Estimation when consumers are requiring more broadcast R 4 channels and VOD services in HD. a Noise t Reduction 3 e Advanced Pre- As the subscriber volume grows, using processing (M 2 MPEG-2 compression for HD will result in b p 1 bandwidth bottlenecks in the networks. To solve s) this problem, increasingly efficient compression 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 algorithms will be required to satisfy this Year consumer demand. Algorithms such as WM9V and MPEG-4 Part 10 have the potential to Figure 1 – MPEG-2 bit rate for standard outperform MPEG-2 by up to 50%, meaning definition broadcast quality picture over time. that a 50% data reduction to deliver the same quality picture is possible — taking full A high definition television (HDTV) video advantage of network bandwidth and increasing picture has 4-6 times more information to be revenue generation possibilities. This paper will processed than a standard definition picture discuss advanced video coding techniques and (horizontal resolution x vertical resolution x how they apply to HD to enable bandwidth frames per second), as the bit rate for a efficient deployment of HDTV for both standard definition picture reached the 3- broadcast television and VOD. 4Mbps (Megabits per second) range in 1998 then it became feasible to deploy HDTV EVOLUTION OF MPEG-2 BIT RATES services within the bit rates available on terrestrial, cable and satellite The MPEG-2 standard [1] reached transmission platforms. commercial deployability in 1994 and has since been widely adopted for standard We can see from the curve of Figure 1 that definition television (SDTV) broadcast and on- each new technique and technology leap has demand services, becoming the defacto returned less of a bit rate efficiency professional broadcast digital video improvement as we approach the fundamental compression standard. Since 1994 advances in limits of performance of the MPEG-2 technology, systems design, implementation compression algorithm. With continuing efficiency and video pre-processing techniques development we are likely to only achieve a further 10% MPEG-2 efficiency improvement bit rate between a number of channels to at a commercially viable cost. This places a optimize picture quality verses bit rate. As the limit on the potential bit rate of MPEG-2 based bit rate for a “broadcast quality” video is such standard and high definition services in the a subjective matter a range of bit rates are future to achieve an acceptable broadcast indicated in figure 2. picture - in the order of ~1.75-2.0Mbps for SDTV and ~8-10Mbps for HDTV. It should also be noted that different performances can be achieved between real- Competition from satellite platforms, who time encoding products, required for live TV are launching 30-40 channel HDTV services, broadcasting, and products using non-real time in addition to increasing demands from the encoding processes, that can be employed for customer, for example HDTV Video-On- the creation of stored assets, such as VOD Demand (VOD) content, place continuing movies. pressures on cable broadcasters. The bandwidth available to the home is limited on MPEG- Advanced Advanced any system, including cable, and while “all 2, Video Video digital” system upgrades and reducing the today Coding Coding techniques, techniques, homes per node try to overcome the system st capacity limits they carry with them an 1 promise investment and infrastructure cost penalties. A deployments over time major improvement in coding efficiency would HDTV, 10-16 6-10 Mbps 4-6 Mbps enable many more services to be deployed real- Mbps across existing infrastructures, and this is the time (1) promise of advanced video coding techniques HDTV, 6-8 3-5 Mbps 2-4 Mbps such as MPEG-4 part 10 [2] and Windows non Mbps Media Player 9 Video [3]. real- time SDTV, 2-4 1-2 Mbps 0.5-1 Mbps BITRATES OF ADVANCED real- Mbps VIDEO CODING time

SDTV, 1-3 0.5-1.5 0.5-1 Mbps The nature of the video compression non Mbps(2) Mbps algorithms being used in any of these coding real- techniques being discussed means that the time perceived picture quality of a constant bit rate video service will vary depending on the (1) As evidenced by content samples on Microsoft website, complexity of the picture. A “talking heads” www.microsoft.com sequence, typical in news programming for (2) Note, 3.2Mbps transport (~2.8Mbps video) typically used for MPEG-2 VOD assets today example, is relatively simple to encode – there is little motion or detail changes between Figure 2 – Advanced Video Coding Techniques vs frames – whereas sport material involves both MPEG-2 bit rates, by service resolution. high motion and high detail changes between frames, testing the limits of the coding While there are differences in the algorithm implementation. The reverse of this techniques used in the MPEG-4 part 10 and is also true – a constant quality picture requires Windows Media Player 9 Video coding a variable bit rate. Other system techniques, algorithms, resulting in some differences in such as statistical , try to make video coding artefacts, it has been shown advantage of this by flexibly sharing a pool of through subjective and objective testing [4] that both these techniques produce averagely • Additional block sizes for intra prediction equivalent quality over a range of bit rates and within I Picture. programming material types, therefore no • In-loop deblocking filter, provides no distinction between coding algorithms is made benefit at higher bit rates but has clear in figure 2. It should be noted that broadcast advantages at bit rates lower than video applications are most likely to use the traditional MPEG-2 operating ranges. “Main Profile” of MPEG-2 part 10 or the “Advanced Profile” of Windows Media Player • Improvements in motion estimation 9 Video. including Tree-structured motion segmentation with a selection of block sizes and 1/4-sample motion TECHNIQUES THAT ENABLE compensation. THE SAVINGS • Additional coding efficiencies from range The new advanced coding techniques of alternative integer transform block sizes, achieve their efficiency improvements over the definition of multiple variable-length MPEG-2 in a number of areas: coding (VLC) tables enabling Context- based Adaptive VLC-based entropy coding • More efficient syntax – saving of bits from (CAVLC), and for MPEG-4 part 10 the fewer and shorter headers, greater range of option for Context-based Adaptive Binary allowable picture sizes, and carriage (CABAC). mechanisms within native IP and with

MPEG based transport streams. • Removal of more information from the CARRIAGE OF ADVANCED CODED picture – improvements in coding techniques VIDEO IN A CABLE SYSTEM and motion prediction tools, including the addition of a more flexible selection of block The advanced coding techniques have sizes. several options of carriage mechanism for transmission. • Hiding artefacts – as bit rates are pushed lower there is an increased likelihood of MPEG Transport Stream blocking artefacts on difficult scenes. Tools such as loop filtering hide the The packetization of advanced coded video blocking artefact edges making them less within the traditional MPEG transport stream perceptible to the viewer, therefore carriage mechanism enables Advanced Coded allowing the bit rate to be pushed lower. services to be broadcast on any existing network carrying MPEG-2 services today.

Using MPEG transport stream also provides a In comparison to MPEG-2 some of the number of other advantages: changes that yield the greatest savings are: • Timing Reference - MPEG transport • Multiple intra-prediction modes for timing references ensure the Field/Frame adaptive coding at picture synchronization of video, audio and time level, and Field/Frame adaptive coding at critical metadata services when the macroblock level (MBAFF) – provides for digitized services are presented to the more flexibility when a picture sequence customer to view. exhibits a mixture of progressive and interlaces characteristics within a • Ancillary data carriage - Other MPEG field/frame. transport related standards also provide a definition for the carriage of ancillary efficiencies over MPEG-2 combined with next services such as vertical blanking interval generation transmission networks will enable data, such as and V- cable operators to further provision advanced chip information. HDTV services to their customers.

• Audio choices – there are multiple

audio defined within various REFERENCES standards and specification which utilize

MPEG transport carriage today. Combined 1. ISO/IEC 13818 International Standard, with the commonality of the MPEG timing "Generic Coding of Moving Pictures reference this enables an operator to mix and Associated Audio Information" and match video and audio codecs to meet their needs. 2. JVT, N5555: Draft Text of Final Draft International Standard for Advanced Video Coding (ITU-T Rec. H.264 | IP Carriage ISO/IEC 14496-10 AVC), Pattaya, The packetization of Advanced Coded March 2003 video services within a native IP transport 3. Microsoft Digital Media website: removes unwanted overhead (header tax from www.microsoft.com/windows/window Advanced Coded Video packets over MPEG smedia/ transport encapsulated into IP frames) when 4. In-depth review of advanced coding Advanced Coded Video services are intended technologies for low bit rate broadcast to be transported over Internet Protocol based applications, J.Bennett & A.Bock networks. (TANDBERG Television), IBC 2003

conference proceedings. CONCLUSION

The major improvement in coding ACKNOWLEDGEMENTS efficiency that are being achieved with first The author would like to thank Ping Wu generation MPEG-4 part 10 and Windows and Alois Bock, TANDBERG Television, for Media Player 9 video codecs will enable many their input and assistance with this paper. more services to be deployed across existing Windows Media 9 Series is a trademark of infrastructures. The efficiency improvement Microsoft Corporation. will further improve as more research and development resources and time improve each CONTACT INFORMATION generation of product implementation. While the support for MPEG transport stream For further information regarding this paper carriage provides an answer for existing please contact: networks, the native IP carriage for next generation networks will become more TANDBERG Television Inc prevalent over time. The IP carriage 12633 Challenger Parkway, Suite 250 mechanism allows a migration to an IP based Orlando, FL, 32826 core network, or even a Switched Digital Tel: +1 407 380 7055 Video over QAM network to achieve Email: [email protected] infrastructure cost savings or provision a greater number of services over a bandwidth limited edge. The combination of compression