Transcript
S4C Technical Requirements – High Definition
January 2010
Introduction S4C has a High Definition Policy and High Definition Guidelines for Producers that were published on 6 August 2006 (updated in 2008) and copies can be found on the following link: http://www.s4c.co.uk/production/downloads/guidelines/e_manylderuwch.pdf S4C needs to ensure that any high value HD programme commissions awarded are technically optimum to protect our investment. These technical requirements are encompassed in these documents and reviewed from time to time. As High Definition production equipment and transmission standards are rapidly evolving at the current time it is incumbent on S4C to keep this technical requirements document up to date with the evolving needs. It is therefore essential that any companies delivering High Definition programs to S4C work to the latest version which is on our website and updated regularly, so they are fully aware of the current requirements. High Definition transmission S4C has a policy of commissioning HD content in order to build up our library of HD programming for future HD transmission. S4C therefore needs to ensure that any high value HD programme commissions awarded are technically optimum to protect our investment. Progressive (p) versus interlaced (i) The existing interlaced TV system is a legacy from an engineering necessity in the past. Better quality can be achieved by progressively scanned pictures which are now possible. So it is highly desirable to leave the old interlaced legacy behind when moving into the new HD standard. Modern large displays also handle progressive pictures far better as they are actually progressive displays internally. Graphics and text (rollers and crawls excepted) are also much better portrayed on progressive rather than interlaced systems. Therefore it is the aim that ultimately HD will use a progressive acquisition, post and transmission format as opposed to interlaced. This may finally become 1920x1080p50 (referred to as 1080p50) as transmission technology advances. This, although ideal for all types of HD programme is not yet achievable due to the high bit rates required. Thus in reality HD transmissions will start as 1080i25 and 720p50, and when the economics and technology support it, move to the ideal of 1080p50. High Definition production In order to retain the best quality possible for HD masters, it is a sensible requirement that any future HD commissions be shot and post produced in as high a quality as possible. This would ideally be 1080p50. However, as already stated this is not practicable at present due to technical and budgetary constraints. The following table lists the key HD formats and S4C’s requirements relating to them.
Format 1280 x 720p50 1920 x 1080i25 1920 x 1080p25 Varicam 24P 1920 x 1080p50
S4C requirement Yes Yes until further notice Yes Yes No Yes – future
Usage guide Until further notice See note below Drama /Docs, Film look Natural History For all material – in future
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The production format of choice for S4C will therefore be 1920x1080p25 for productions such as drama, documentary etc. that may wish to achieve a film look. This is progressive, and retains the highest resolution, at an acceptable bit rate.
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We would prefer to avoid wherever possible the use of any HD interlaced standards for acquisition. However, from a pragmatic perspective and until 1080p/50 equipment is freely available, S4C will accept 1080i/25 originated production and delivery. We will give reasonable notice of any changes in this respect.
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It is fully accepted that although equipment may not be available to do all these progressive formats yet, it will become available in the near future. Therefore it is important that S4C’s future preferences in this area are made known to all interested parties as early as possible. The above is therefore intended as a guide for those companies and individuals that produce HD programmes for S4C in future.
Supporting the above rationale is the fact that progressive pictures will convert to interlaced for transmission and display purposes where necessary, and will retain better quality than when interlaced is converted to progressive. In future, as HD equipment becomes technically more developed, and more cost effective, S4C’s requirement will move towards a 1080p50 progressive format for all HD acquisition. The decision on when this will happen will not be taken for some years from now, and reasonable notice of this intention will be given. Throughout, the aim is to retain as high a quality on the final master as possible, within commercial realities. Frame rates - 50 versus 60 Throughout the above, the frame rates have been stated as 50 or 25, the European standard. However, as much of the material co produced will be destined for sales to North America and Japan, they will be requiring the frame rate to be 60/30 (actually 59.94) so their standards will be 1080i30, 1080p30, 720p60, 720p30 and in future 1080p60 (equivalent to the European future 1080p50). Although this is not ideal for S4C’s purpose, commercial reality may dictate that S4C will have to accept a co production in a non European frame rate. In this case S4C will be receiving a down converted SD 625i master for transmission, and a 60/30 frame rate HD master for archive. In future should it be transmitted in HD in the UK it may have to be converted from any of the HD 60/30 frame rates to our European HD 50/25 transmission standards. As HD standards conversion is still improving rapidly, this HD to HD conversion is best delayed and should be undertaken nearer to the time it is needed for transmission. This will allow use of the latest generation of converters, and hence the best possible quality of conversion. The need for such cross conversion is obviously best avoided if at all possible, as any frame rate conversion will lead to a reduction in quality. •
For commissions that are destined for Europe, acquisition in the 50/25 rate will be S4C’s requirement.
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24p Frame rate - at present it is not S4C’s intention to support 24p origination.
Graphics This can often present a problem when converting from HD standard to SD. Depending on detail and font sizes it may often not be acceptable to merely convert the existing completed master HD material in either a down or cross conversion process. Hence a clean (no text or graphics) version of the HD master may need to be retained together with the graphics and text files to enable them to be keyed into the finished down/cross converted masters. Safe areas All basic parameters for safe areas etc can be taken from the current specification for wide screen production as there is no fundamental change to these when considering high definition TV. This refers especially to safe graphics areas. The only change here is the slight tightening up of the over-scan figure used for tube displays that can be achieved when considering Plasma and TFT flat screens. Any new over-scan figure and consequent change in safe area can only be implemented in production when the large majority of tube displays in use have been replaced and a new standard is officially accepted and published. This is still some years away. Audio It is increasingly common to have surround sound on HD productions to add greater impact to the production. 5.1 surround sound and 5 is the preferred option for S4C in such circumstances. Dolby E During the last year there has been a swing to Dolby E encoding as an audio delivery requirement by various broadcasters. This does enable further post production and processing to be undertaken as Dolby E can maintain the quality of the audio for up to 10 encode /decode processes. So is ideally suited to a distribution and post production model. Dolby E is a professional encoding process and never used in the consumer domain so is never transmitted. The Dolby E is therefore finally decoded and re encoded to Dolby digital for transmission. Where surround sound is specified, S4C will specify Dolby E for the final delivered master tape. Production companies may also wish to consider using Dolby E to facilitate post production, distribution and sales. Should S4C’s needs change in this respect, we will give adequate notice to suppliers of any such change. Delivery Delivery to S4C for transmission will until further notice also request a version to be in SD full height anamorphic (widescreen) Digi beta, as at present. With stereo audio. Hence the finished HD master will need to be down converted to SD by the production company, and (if necessary) the SD graphics inserted onto the SD master, post down conversion. HD tape format S4C will not be prescriptive about the tape format used for HD production. At present and until further notice, HDcamSR, HDcam, DVCPRO100, XDcam HD 422 50Mbs and Varicam for variable frame rate requirements are all acceptable. Until 31 December 2010 delivery will be accepted on HDcamSR and HDcam. Post this date only HDcamSR will be accepted for delivery of HD material. The HD transmission platform is still rapidly evolving. Currently, most HD transmissions are settling on using the 1080i25 form. S4C will align with this trend. Therefore, to simplify the transmission operation, all delivered HD material should be set to 1080i25 when the final dub is created for delivery, whether the programme was acquired in 1080125 or 1080p25. If the original material was acquired in 1080p25 for filmic look reasons, rollers and moving captions should be added in 1080i25 to prevent judder.
Live programmes For live programmes the feed to the link to S4C should again be set to 1080i25 to eliminate the possibility of any errors at final transmission HDCam and HdcamSR Audio arrangement for delivery Format HDcamSR HDcamSR HDcamSR HDcamSR HDcamSR HDcamSR HDcamSR HDcamSR HDcamSR HDcamSR HDcamSR HDcamSR
Format HDcam HDcam HDcam HDcam
Track 1 2 3 4 5 6 7 8 9 10 11 12
Description Stereo mix left Stereo mix right Dolby E final mix Dolby E final mix Front left Front right Centre LFE Surround left Surround right Second Language L or Audio Description Second Language R or Audio Description
In the absence of second language audio, or audio description, tracks 11 and 12 must be blank. Tracks 5 to 10 carry the discreet 5.1 surround sound. The Dolby E track allocation is ordered as follows: Dolby E Track 1 2 3 4 5 6 7 8
Audio Front left Front right Centre LFE Surround left Surround right Not used Not used
Note: Dialnorm settings between -22 and -27 are acceptable Compression S4C will expect HD production and delivery (where applicable) to avoid any undue loss of quality due to the excessive use of video compression. As a guide S4C will not accept production (or delivery) processes that utilise a bit rate of less than 50 Mb/s for high value productions. There may however be valid reasons to allow special relaxation of this rule for programs that are considered to be of lower value or require equipment that is smaller, and hence more portable or less intrusive for acquisition. In this case, acquisition and production equipment in the group that utilises bit rates of the order of 35Mb/s will be acceptable. Needless to say that attention to maintaining quality at its highest level should be borne in mind for all productions but especially so for HD productions that have acquired at the lower 35Mb/s bit rate. For information it should be noted that Sky HD specifically imposes a requirement of 50Mb/s and ½” or greater sensors to be used in acquisition for content to classify as full HD. This is not an uncommon view amongst many broadcasters. Hence the above relaxation offered should be used with care and only when particular circumstances for the production warrant it. It is fundamental and important that what is essentially the “quality” level that is referred to in this section is discussed, agreed and documented at the commissioning stage to avoid any costly misunderstandings later.
Use of HDDV This is not acceptable as a format for high value high quality HD origination. It is accepted that it has a place for certain types of commissioned content where its small size will be advantageous. It is expected that in this case HDDV would be used as specific inserts in to a main programme shot on a full quality HD standard. HDDV has another very valuable use however and that is one of providing a source of true 16x9 high quality widescreen material in SD. This is in preference to the use of DV origination camcorders. S4C would encourage use of this technology to achieve this end. Communication Due to the complexities involved and the speed of change of this area of technology, it is advisable that any company planning to originate a programme for S4C in HD should discuss the project with S4C at an early stage. Contact for further details If you require further details or wish to discuss any aspect of the above then please contact: For technical enquiries:
For other enquiries
Transmission and Distribution Tel. 029 20741200
Business Affairs 029 20741479
