MPEG Implementation Guidelines Ken McCann I am going to give an overview of the implementation guidelines. First the basic philosophy of them. Secondly a brief history of how they have developed over time. Finally I will highlight some of the things that are developing now that have particular relevance for Australia. 1

DVB Family of Standards The DVB family of standards use a common baseband specification for all transmission channels: terrestrial cable satellite microwave This is important to facilitate interoperability. For example if I am a cable operator we can have direct digital turn around of signals received terrestrially or by satellite without having to transport.

DVB Data Containers MPEG Transport Stream is used to provide DVB “data containers” which may contain a flexible mixture of: video audio data services You can mix the services in a flexible way so that depending on the particular requirements of your application you can have different mixtures of audio and video.

Examples of DVB Data Containers Channel bandwidth can be used in different ways: SDTV 1 SDTV 2 SDTV 3 SDTV 4 SDTV 5 Multiple SDTV programs Single HDTV program HDTV 1 SDTV 1 HDTV 1 Simulcast HDTV & SDTV Focusing on the TV aspects. There are different ways the channel bandwidth can be used. As has been done in the UK, you can have a multiplex which has multiple standard definition programs within it. You can also have a multiplex which contains a single High Definition program which is the plan for many situations in Australia. There is also the facility to have simulcast, where you cut down a bit on the High Definition to allow the older receivers that are there to decode the Standard Definition variant. This may well be used in the future in the UK when the analog transmissions are turned off. The plan in most of Europe is for High definition to be introduced as a second phase as part of the analog turn off.

MPEG Implementation Guidelines First version of DVB’s “MPEG Implementation Guidelines”, ETR 154, was published in 1995 Initial emphasis was on SDTV Revised in 1997 to include HDTV SDTV and HDTV versions of a program may be simulcast 1999 revision is due to be published shortly and includes options for: Active Format Description MPEG Audio Metadata Dolby AC-3 audio The 1999 revision is in the pipeline now and has been very heavily influenced by the requirements for the Australian market. I would like to single out Geoff Tomes for mention as “honorary editor in chief” of this. The very efficient process means that the Australian specification and the DVB specification are remarkably well coordinated. The three main things that have been added in, apart from tidy-ups The Active Format Description is particularly relevant in the UK allowing a compromise between 4:3 and 16:9. MPEG Audio Metadata enhancing slightly the facilities available using MPEG audio. The one that has most relevance for Australia is the AC-3 audio.

Main Features of Video Flexibility of the generic MPEG-2 video standard is maintained to the maximum extent practical Bitstreams and IRDs are classified as SDTV or HDTV Applications are classified as contribution or distribution I will be focusing primarily on the distribution which is covered in ETR-154. Contribution is going to be an additional technical report. The decisions on what the content will be, have been made, it just has not been written yet.

Primary Classification of DVB IRDs and Bitstreams If we take a SDTV distribution IRD this will be capable of receiving SDTV distribution bitstreams, and that’s all. Take a HDTV distribution IRD it can receive SDTV bitstreams or of course HDTV bitstreams intended for distribution applications. If you look at the HDTV contribution IRD it is of course the most flexible and can receive anything.

MPEG Profiles and Levels 422P@HL MAX. BIT-RATE 300 Mbit/s HP@HL 100 Mbit/s MP@HL HP@H14L 80 Mbit/s 60 Mbit/s SSP@H14L 40 Mbit/s This diagram is a summary of the profile and levels of MPEG. “Profile” is what has been used in MPEG to mean a subset of the syntax, for example if you look at the main profile, which is the one most commonly used, the difference between it and the simple profile, is that bidirectionally coded frames can be used. Similarly as we go up the scale of profiles, extra functionality is added. In almost every case, but not in the 4:2:2 case, it’s an onion ring where each one further down the scale is a simple sub-set of the ones further up the scale. “Levels” is a term that is used for constraints on parameters. Typical parameters that this covers are Video resolution or Bitrate. The diagram is attempting to highlight the bitrate by the height of the cylinders. If we look at the MPEG Main Profile at Main Level the maximum allowed bitrate for that is 15 Mbits/s, the maximum allowed video resolution corresponds to Recommendation 601 in it’s 25 & 50 Hz flavors. The next one in yellow is Main Profile at High Level, this is what has been chosen for High Definition TV. In addition to having the enhanced resolution, you are allowed a higher bit rate which is 80 Mbits/s. If we look at the 4:2:2 Profile (Green). In addition to being able to have 4:2:2 encoding as well as the 4:2:0 (In other words having full horizontal resolution relative to Rec 601) you are also allowed to have a much higher bit rate. The reason for the much higher bit rate is, in addition, in a contribution application wanting to have the highest possible quality prior to transmission, you may also want to have more frequent occurrences of Intra-coded frames which are the points at which you can make editing. This results in less efficient coding, so therefor you need a higher bit rate to maintain the quality. MP@H14L 422P@ML 20 Mbit/s HP@ML HIGH SNRP@ML MP@ML HIGH-1440 SP@ML 4:2:2 LEVELS SNRP@LL MAIN HIGH MP@LL SPATIALLY SCALABLE SNR SCALABLE LOW PROFILES MAIN SIMPLE 4

DVB Guidelines for HDTV Distribution Utilises full flexibility of MPEG MP@HL Mandatory upper limits of: 1152 lines per frame 1920 luminance samples per line 62,668,800 luminance samples per sec. Recommends use of: 1080 active lines per frame 1920 luminance samples per line If you take the 30 Hz variant and multiply the upper limit numbers together, you end up with a number which is bigger than 62.7 M samples/sec. That’s intentional, this has been designed so as to cope with the combination of the likely events of frame rate and maximum resolution being different, of course, in the NTSC and PAL/SECAM historical world. We have a single recommended format for the source to encourage interoperability and make it easier for people to transfer programs from one part of the world to another. In both the 25 and 30 Hz frame rates it is 1080 active lines per frame and 1920 luminance samples per line. That seems to be what is emerging as the new studio standard. In the actual transmission you may well choose to sub-sample it in the transmission process and then up-sample again at the decoder. That’s something that happens very commonly in MPEG encoders, simply as a means of trading off perceived resolution against perceived artifacts. 5

DVB Guidelines for HDTV Contribution HDTV contribution encoders produce bitstreams that comply with 422P@HL or MP@HL HDTV contribution IRDs are capable of decoding both 422P@HL or MP@HL bitstreams. Recommends use of: 1080 active lines per frame 1920 luminance samples per line Contribution is similar to distribution but you may use the 4:2:2 profile at High Level 5

Chromaticity SDTV needs compatibility with legacy displays, so default SDTV chromaticity in DVB is: same as PAL for 25Hz same as NTSC for 30Hz HDTV has unified world-wide chromaticity and no legacy displays default is BT.709 for both 25Hz and 30Hz simulcast allows mixture of legacy chromaticity for SDTV and BT.709 for HDTV Often neglected until you get it wrong, then it becomes very visible.

Main Audio Features of DVB IRDs 32 kHz, 44.1 kHz and 48 kHz sampling All IRDs support MPEG stereo Layer I and Layer II decoding IRDs may also optionally support: MPEG-2 backwards compatible multi-channel decoding Dolby AC-3 decoding In the overall DVB sense Dolby AC-3 support in the IRD is an option, in particular application areas of particular countries it may be something rather stronger than an option.

Main Audio Features of DVB Bitstreams In general, audio content is encoded using MPEG stereo Layer II, even if it is also encoded using Dolby AC-3 In specific situations where all IRDs are required to support Dolby AC-3 then simulcast of MPEG stereo is not required

Conclusions DVB standards fully support HDTV by terrestrial, cable, satellite or microwave delivery Australia will lead the way to HDTV in the DVB World