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Old 17th April 2014, 10:30   #1  |  Link
Sci-Fi-Fan
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Interlaced Video

Hello All

Something that's been bugging me for a very long time that I'm hoping you guys can explain for me.

The majority of television networks, production companys in the United Kingdom like the BBC and ITV are still using Interlaced Video (or Hybrid Versions) to produce all their movies, programming ect,
Whereas in the USA everything is produced using progressive scan.

To my understanding (Taking into account the advance of modern Hi Resolution HD televisions) Interlacing is an obsolete technology.

So why is the UK still using this obsolete technology?

The only thing I can think of is the cost of updating / replacing out of date equipment...

If anyone can explain this I'd much appreciate it.

Thanks
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Old 17th April 2014, 11:06   #2  |  Link
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Originally Posted by Sci-Fi-Fan View Post
Whereas in the USA everything is produced using progressive scan.
what do they mostly use for everything? 1080p30, 1080p50, 1080p60 , .... ?
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Old 17th April 2014, 11:32   #3  |  Link
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Interlacing

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Originally Posted by smok3 View Post
what do they mostly use for everything? 1080p30, 1080p50, 1080p60 , .... ?
The most common I've seen is 1080p 24.976 or 29.9??
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Old 17th April 2014, 12:06   #4  |  Link
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you need more bitrate for full frames (prorgessive) which means more money to spend on satellite bandwitdth for example
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Old 17th April 2014, 15:45   #5  |  Link
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Quote:
Originally Posted by Sci-Fi-Fan View Post
To my understanding (Taking into account the advance of modern Hi Resolution HD televisions) Interlacing is an obsolete technology.

So why is the UK still using this obsolete technology?

The only thing I can think of is the cost of updating / replacing out of date equipment...
This is a bit complex - interlace is a way to compress bandwidth of the video signal and it is matched with human perception system quite well.
You can see interlace as adaptive bandwidth compression with exchange of bandwidth between temporal/spatial resolution - for static pictures - interlace can provide almost full video bandwidth (reduced by proper to interlace system Kell factor), for dynamic motion vertical resolution is reduced in favor to have more fluid motion (i.e. increased temporal resolution) - also in this place Kell factor reduce overall resolution (less than for interlace).

Why it is still used? Why movies are still using 24fps technology nowadays?

Yes, there is a small progress in cinema industry towards higher frame rates but still, 24 fps is most used format worldwide for cinema distribution and TV use cinema as source (one of main sources) - for this purpose - interlace TV seem to be quite perfect even for HD - cinema tape can use almost full spatial bandwidth where life events (such as sport transmissions) can use higher temporal resolution - TV trying to be universal medium (under some limitations) - i would say - lot of U.S is still interlaced (1080i) some of them are progressive (720p) - U.S. have own limitations (as early adopters for HD - MPEG-2, 8-VSB with netto bitrate up 19.3904Mbps for Audio+Video+PSI/SI+metadata).

Interlaced is no longer considered for UHD but HD is a different story... we are in transition period to high fps, high resolution sources.

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Originally Posted by Mounir View Post
you need more bitrate for full frames (prorgessive) which means more money to spend on satellite bandwitdth for example
In fact (considering same amount of pixels at screen per second) less by approx 30% (case 1080p30 vs 1080i30).

Last edited by pandy; 17th April 2014 at 15:49.
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Old 18th April 2014, 11:45   #6  |  Link
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I think you'll find that most 'non live' high-def content in the UK is captured as progressive... It's just transmitted as interlaced.

I have DVB-T2 and DVB-S2 tuners in most of my TV's and quite often I've noticed that the same content is flagged as progressive on one transmission platform but flagged as interlaced on the other
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Old 22nd April 2014, 08:24   #7  |  Link
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so the conclusion could be that early adopters (mostly due to not using AVC) were almost forced to use progressive low-framerate stuff (up to 30p) including us,

now the question is if less-early adopters got it right by choosing interlaced stuff instead of just going high-framerate (which is costy in post and probably otherwise bandwidth problematic). I do hope it was more than just that thought....

So the comparision would be to compare say 720p50 and 1080i25 and i can tell you that 1080i25 would probably win (looking at the latest Olympics at least).
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Old 22nd April 2014, 16:50   #8  |  Link
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Issue is more complex - some of European broadcasters use for MPEG-2 dynamic progressive/interlace switching (GOP/GOP adaptive way) where H.264 have MBAFF to deal with this problem at macro block level thus at least in theory is more efficient.

1080i seem to be more popular thanks to higher "flexibility" - for cinema tape it can provide quality almost like 1080p where for sport it can worse than 720p but still less problematic as nothing need to be changed in production chain...
If broadcaster encoder is "smart enough" then 1080i seamlessly integrate with SD sources, movie tape etc.
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Old 24th April 2014, 14:35   #9  |  Link
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Originally Posted by SeeMoreDigital View Post
I think you'll find that most 'non live' high-def content in the UK is captured as progressive... It's just transmitted as interlaced.

I have DVB-T2 and DVB-S2 tuners in most of my TV's and quite often I've noticed that the same content is flagged as progressive on one transmission platform but flagged as interlaced on the other
The Freeview HD (DTT/DVB-T2) encoders used by the BBC auto-detect pure 25p progressive content in a 50i stream (all sources are 50i streams), and encode it as 25p.
http://www.bbc.co.uk/blogs/legacy/researchanddevelopment/2011/04/software-upgrade-for-bbc-hd-on.shtml

25p is not part of the UK satellite standard, so everything is 50i on DSat/DVB-S2.

It makes little difference.

Cheers,
David.
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Old 24th April 2014, 14:37   #10  |  Link
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Originally Posted by Sci-Fi-Fan View Post
The most common I've seen is 1080p 24.976 or 29.9??
There is plenty of 720p60 and 1080i60 broadcast in the USA. You just haven't watched the right broadcasts e.g. live, sports, news, talkshows, etc.

The situation is no different from in the UK with 1080i50, apart from certain US networks using 720 rather than 1080, and all of them having to cope with 3-2 pulldown.

Cheers,
David.
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Old 3rd May 2014, 23:30   #11  |  Link
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Originally Posted by pandy View Post
Issue is more complex - some of European broadcasters use for MPEG-2 dynamic progressive/interlace switching (GOP/GOP adaptive way) where H.264 have MBAFF to deal with this problem at macro block level thus at least in theory is more efficient.
MPEG-2 has something similar to MBAFF as well and is used almost always. I have never seen MPEG-2 field mode encodes outside of test clips.
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Old 4th May 2014, 07:33   #12  |  Link
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I'm referring to Blu-Ray disk content only.

Every Blu-Ray I've brought of a USA TV Series or Hollywood Film is encoded as 1080P.

Every Blu-Ray I've Brought of A TV Series produced for the UK Market is encoded using 1080I.

For example the Blu-Ray for the TV Series Merlin produced for the BBC is encoded using MBAFF.

But when converting the content to media files only the closing credits are interlaced, The rest of the frames were 1080P full frames.

Other UK Blu-Rays like Doctor Who are entirely encoded using 1080I.
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Old 4th May 2014, 13:47   #13  |  Link
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Originally Posted by Sci-Fi-Fan View Post
I'm referring to Blu-Ray disk content only.

Every Blu-Ray I've brought of a USA TV Series or Hollywood Film is encoded as 1080P.

Every Blu-Ray I've Brought of A TV Series produced for the UK Market is encoded using 1080I.

For example the Blu-Ray for the TV Series Merlin produced for the BBC is encoded using MBAFF.

But when converting the content to media files only the closing credits are interlaced, The rest of the frames were 1080P full frames.

Other UK Blu-Rays like Doctor Who are entirely encoded using 1080I.
That's because 1080p@25 isn't allowed on Blu-Ray.

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Old 4th May 2014, 16:21   #14  |  Link
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And they are only flagged as i. Source is in most cases either real 25p or speed up 24p. When done in proper way, whole encoding/prefiltering is progressive and MBAF is not used, as it's not needed. Some encoders have special options for making 25p flagged as 50i streams, shame that so many operators have no clue how to use it.
If you have good plyer/TV you will be watching 25p (it's just flagged as 50i as 25p is not in BDspec).

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Old 5th May 2014, 23:01   #15  |  Link
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Quote:
Originally Posted by Sci-Fi-Fan View Post
But when converting the content to media files only the closing credits are interlaced, The rest of the frames were 1080P full frames.

Other UK Blu-Rays like Doctor Who are entirely encoded using 1080I.
Some Doctor Who blu-rays (the Specials) were, annoyingly, only released as a 60i conversion around the world, including in the UK.

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Source is in most cases either real 25p
I'm not so sure there's ever any such thing when it comes to "PAL" land. If the end credits are i, as invariably they are, isn't the whole thing really i?

25p is effectively (barring minor differences in how chroma is done) a subset of 50i, hence 25p not being in the blu-ray spec.
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Old 6th May 2014, 09:34   #16  |  Link
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I'm not so sure there's ever any such thing when it comes to "PAL" land. If the end credits are i, as invariably they are, isn't the whole thing really i?
no, not really.... it's done by progressive frame segmenting, which means the decoder can put the fields together and get perfect 1080p25 out of 1080i50...
it's the same thing what you get in TV in PAL countries... it technically is 1080i50, but you get 1080p25 at the end... better than in the US where everything is telecined and you gotta use filters to IVTC...
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Old 6th May 2014, 10:08   #17  |  Link
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I'm not so sure there's ever any such thing when it comes to "PAL" land. If the end credits are i, as invariably they are, isn't the whole thing really i?
They do it, so they roll better

What they should do is to offset them few lines, like they do credits for cinema or simple leave them as 25p.

BBC is not that great. They quite often deliver 50i, which is in reality 25p, but with one missing "field"! This is proper mess up. It happens when they load 25p source to NLE, which interpreters it as i, so you loose half vertical resolution.
This is bad and can't be fixed. Some big authoring house came to conclusion with BBC people that this if fine Sorry, but it sounds like a joke. I use to receive many masters like this and all of them were rejected, but at the end (after sometimes weeks of debate) it would come back fine

Last edited by Guest; 6th May 2014 at 22:53. Reason: 4
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Old 6th May 2014, 10:25   #18  |  Link
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Some Doctor Who blu-rays (the Specials) were, annoyingly, only released as a 60i conversion around the world, including in the UK.
Reason is simple- world wide compatibility. It makes whole process way easier and cost effective. Does it provide best quality- no. They coudl shot at 24p, but than it would not be UK broadcast friendly
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Old 6th May 2014, 22:49   #19  |  Link
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BBC is not that great. They quite often deliver 50i, which is in reality 25p, but with one missing "field"! This is proper mess up. It happens when they load 25p source to NLE, which interpreters it as i, so you loose half vertical resolution.
As far as I know this shouldn't be allowed these days. In the past yes, Top Gear SD was quite commonly doing this. Anyway I guess you can ask them at the next DPP meeting if you're going again.

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Old 7th May 2014, 10:47   #20  |  Link
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It was veeery common and included basically all post houses. Maybe it has changed over last years or so.
I should be going on some of the next DPP meetings.

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