[opendtv] Re: 625 video quality is good enough....
- From: jeroen.stessen@xxxxxxxxxxx
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 19 Oct 2004 08:47:26 +0200
Hello,
From: "Dale Kelly" <res0xtey@xxxxxxxxxxx>
>> I agree, 50/60P should be the ultimate format when technology can
>> accommodate. However, I don't know that it can be done in a transport
>> constrained to MPEG2.
Alan Roberts:
> Indeed, MPEG2 would struggle, but a truly anonymous transmission system
> could carry MPEG4, WM(whatever version) etc, and by thoroughly future
proof.
> What we need to standardise on is the transport stream, not the scanning
> format. Let's try to get it right this time.
I've been thinking about a proposal like this:
Transmit a base layer in today's standard, e.g. 720p@50 in
MPEG2. Reserve data types for enhancement layers in yet
undefined standards, e.g. for the difference signal between
1080p@50 and 720p@50 in MPEG4.10 (AVC) or in WM9, whatever.
Current receivers will ignore the extra data if and when
it comes, and future receivers will be able to use it to
render the next higher level.
One can extend this principle with more layers below (e.g.
480p@50) and above (e.g. 1620p@50). The advantage of an
extra layer below is that cheaper/smaller displays can
simply ignore the higher resolution data, instead of first
decoding it and then down-sampling. The advantage of extra
layers above is that as the art of compression advances
the lower layers will compress more efficiently and thus
create room for the future higher layers "for free".
And you would never lose compatibility with older decoders.
Lower layers should preferably be transmitted with more
robustness (like more forward error correction bits), to
maintain a watchable picture under bad reception conditions
like mobile, portable, bad weather, interference, etc.
My point is: don't write fixed standards with a short list
of "magic numbers", but write a standard that can grow.
Then you won't have to abandon it after every few years.
Here in the lab we are now receiving 1080i@50 satellite
transmissions on 768p displays. It's easy to do it right,
and it's also too easy to do it wrong. Enough said...
Best regards,
-- Jeroen
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