Wednesday, July 02, 2008

The HD Masters, part 2

"I want my 1080P"

I'm glad that the Beeb and Sky got behind 1080i as a start with 1080p as the eventual intention. Here are a few of the observations the speakers made on that subject;

At high compression rates (especially sub 8-Mbits MPEG4) progressive pictures look better than interlaced - A lot of the broadcasters who got behind 720P bang on about this but it seems a poor reason to settle on a technical spec that is 'better' because it avoids the current limitations of the technology better than a visually better option.

For production purposes 200Mbits should be considered the minimum. JPEG2000 is very good at these data rates and subsequent delivery at H.264/AVC-MPEG4 (even at 8Mbits) shows no artifacts.

Sky are assuming that as soon as 880MBit HDCamSR machines (Sony HDW-5800) become commonplace they will specify 1080P as their delivery spec.

Part of the 1080P spec included 24P! EBU tech document 3321 covers this.

BluRay has of course been 1080P from the outset - the chap from the 'packaged media' (the new name of DVDs?!) industry body told us that they assume they have a five-year head start on the broadcaster and they intend to make BluRay a premium format using this as their main marketing point.
Currently BluRay (both disks & machines) are outselling DVD (for a comparable point in the format's life, say 1997) by six to one.

Coding, Mux & delivery;

In the past decade the venerable MPEG2 transport stream has done good work - but a combination of newer codecs - some variant of MPEG4 - probably the AVC or H.264 codecs (which subjectively halves the required bitrate at both SD & HD) and better multiplexing (moving the QAM64 and DVB-T2 transmission) means that there could be a lot more space for channels. However - with the analogue switch-off nearly on us and the whole country buying MPEG2 decoders & TVs another change (without the associated benefit of moving to HD) seems unlikely.

The representative of OFCOM did a good presentation of how Mux-B will be liberated when the analogue switch-off is complete. This will be a dedicated HD Mux and since it will start with DVB-T2 power, QAM64 channel-packing and AVC we'll be able to pack four 9Mbit HD channels in. One will go to the Beeb and the others will probably be awarded to ITV-HD, Channel 4 and five-HD.
As the other Muxes move over the DVB-T2/QAM64 (but remaining at MPEG-2 TS for compatibility) - remember OnDgital was QAM64 and it wasn't until the Beeb re-launched as FreeView that they switched to QAM16 for more reliable coverage. The T2 spec allows for more transmission power and any current Yagi aerial will deal with that.

Currently none of the manufacturers offer a StatMux for MPEG-4 - BBC R&D have one they've built themselves and Sky reckon they'll be testing some prototypes before the end of the year. Since Mux-B becomes available Q4 of 2009 it seems there is a bit of time.

HD Production observations;

There were several broadcasters in attendance - here are a few of the things they said;
The EBU maintain that for the current crop of manufacturer production codecs at 1080i nobody should go below 185Mbits - that's the highest data rate that Avid DNxHD offers and you can drive Avid ProRes a lot lower! Where does that leave DVCProHD?!
France-2 had a very interesting set of footage from the Roland Gaross tennis last year. They had the same court shot at 16x9 HD and 16x9 HD shot-to-protect 4x3. The latter was so much busier as the cameraman tried to keep the action the centre of frame. It was all a lot tighter focused and I realised how much more like the world 16x9 is. Of course when you come to transmit stuff shot-to-protect 4x3 the codecs fall apart!

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