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Any chance of 1080p25 on BBC HD on Freesat


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Old 07-04-2011, 20:21
Captin
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I think you're missing the point here a little Nigel.

The quicker you flash frames through the less noticible any artefacts are to the brain. So in actual fact you can get away with far more at 50fps than at 25fps.
Good explanation, do I know you? I think you have been to the same demos, lectures and conferences as me

There is also a factor in that interlaced video, especially 4:2:0 as is usually broadcast really gets in the way of video compression. For the same visual compression level a progressive source uses less bits, it's easier for the encoder to break down.

While it's true that there is no difference between 1080p25 and that same video delivered as 1080i when compression is very low e.g bluray or a 50Mbps studio feed. In any real world hdtv broadcast situation 1080p25 will use look better than it's 1080i equivalent.

Why would BBC HD be using it if there was no benefit?
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Old 07-04-2011, 20:32
SimonBlackham
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eg. If you're shooting 25 frames per second then each frame is 4 hundredths of a second long then you have 4 hundredths of a seconds worth of blur in each frame
:
NO - the exposure does not have to be longer - it can be a series of (less than) 1/50th sec exposures with 1/25th sec between the start of each one - therefore you can get similar motion blur to 50fps - but a slightly jerky framing (not as bad as pulldown for 60Hz TVs) unless you have a TV that can interpolate the 'missing' frames*.
Filmed source at 24/25fps will show progressive motion blur rather than interlaced motion blur which (IMHO) is much more acceptable - no combing and filters to remove it!
The progressive blurring is in the direction of the motion - interlaced blur is often in a different direction dependent upon the direction on the screen and the speed of motion.
The advances in compression engines mean that 1080p50 will be easily broadcastable soon.
Stat-MUXing is a two-edged sword - more instantaneous bandwidth when required - but the MUXing has to be done on the fly and will sometimes fail. Compare this with DVDs or VOD that is not MUXed and the compression engine is not constrained by real-time to get through difficult bits. n+1 stat-MUXing gets better the more channels it has to work on - but also requires greater computing power to MUX more channels (ie greater n ... the +1 is the stream of instantaneously unused video bandwidth). It is therefore a continuously developing art. Combining frequency slots to give 'superMUXes' using 16MHz (or greater) slots would be better if the compression engines could cope - which of course they will in the future.

*a 600Hz TV can show exact fps for 24, 25, 50 and 60 fps.
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Old 08-04-2011, 09:59
White-Knight
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NO - the exposure does not have to be longer - it can be a series of (less than) 1/50th sec exposures with 1/25th sec between the start of each one - therefore you can get similar motion blur to 50fps - but a slightly jerky framing (not as bad as pulldown for 60Hz TVs) unless you have a TV that can interpolate the 'missing' frames*.
I know I was keeping it simple.

You're right. The lower frame rate (25fps) can be distributed between each second either by increasing the duration of the frame or by increasing the amount of time between the frames. Both of which can have their problems as you pointed out. (Higher frame duration (longer shutter speed) = more blur, lower frame duration (shorter shorter speed) = risk of frame jumping ie object travelling a noticible distance during the uncaptured parts of the second with the result that it appears to jump and jerk along rather than move slowly.

Running a high frame rate eg 50fps, reduces both of these problems and increases overall picture quality by dramatically increasing the quality of each individual component still frame.
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Old 08-04-2011, 10:11
2Bdecided
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Some encoder engineers used to think that 1080p50 needed more broadcast bandwidth than 1080i but recent studies have contradicted this. The EBU has been running a trade roadshow for several years to try to re-educate broadcast engineers.
It falls apart in a different way as you reduce the bandwidth. Remember all the UK FTA HD broadcasts are at lower bitrates than the EBU recommends.

You can't necessarily trust all these demos. There's a history of using encoders which aren't tuned for interlaced encoding, while most H.264 encoders are quite exceptional at progressive encoding.

That said, for lots of content at a range of bitrates, on most 50p-capable current displays, 50p can have the edge over 50i. It depends on so many factors though.


The problem is, current STBs can't handle it, and the improvement isn't enough to justify a whole new generation.


Did someone say motion-blurred (e.g. typical 25p) content was harder to encode than sharp content (e.g. typical 50p)? If so, this is just silly. It's high frequency details (as well as movement/change) that cost bits. Blurred pictures don't have any high frequencies.

Cheers,
David.
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Old 22-04-2012, 22:14
bushbox browser
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Back to the original subject.

No Freesat and Sky cannot use this properly as they don't output 1080p. With Freeview HD when the source material is 1080p 25f it will be broadcast as that, then the box will output the signal as progressive for the TV to display.

The main advantage with this is that no de-interlacing needs to take place at all.

I would think that on sat a broadcaster could broadcast in 1080p 25f but as the boxes don't output 1080p it would be interlaced by the box and then de-interlaced by the TV.

There is probably very little difference watching on Freeview or sat but technically Freeview is better set up for this.
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Old 22-04-2012, 23:04
grahamlthompson
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Back to the original subject.

No Freesat and Sky cannot use this properly as they don't output 1080p. With Freeview HD when the source material is 1080p 25f it will be broadcast as that, then the box will output the signal as progressive for the TV to display.

The main advantage with this is that no de-interlacing needs to take place at all.

I would think that on sat a broadcaster could broadcast in 1080p 25f but as the boxes don't output 1080p it would be interlaced by the box and then de-interlaced by the TV.

There is probably very little difference watching on Freeview or sat but technically Freeview is better set up for this.
Without all HD sat boxes having the capabillity to output 1080p50 then according to the BBC for some TV's it will not work.

http://www.bbc.co.uk/blogs/researcha...bc-hd-on.shtml
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Old 22-04-2012, 23:32
DragonQ
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Honestly, outputting 1080p/25 as 1080i/25 (as happens now on Sky/Freesat) isn't a significant problem for good deinterlacers, such as those found in TVs. You wouldn't get a noticeable improvement in image quality if it was outputted as 1080p/25.

The main advantage to the 1080p/25 thing on Freeview HD is that the encoders have to do less work. If the encoder knows content is progressive and can encode it as such, it needs far less bits than if it's just blindly encoding everything as if it were interlaced. Although this would be nice to have on Freesat, it isn't as big of a problem due to the relative abundance of capacity.
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Old 23-04-2012, 02:28
d'@ve
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It would be nice if we the viewers were allowed to judge the benefits of higher frame rates - even if they had to do it at 720p/50. Trouble is that we've never had the chance and that makes me angry because many people would prefer natively recorded 720p/50 to 1080i/p25 (frames).

Getting the highest possible spatial resolution is overrated, given how far most people watch HD TV from. It's temporal resolution that is sub standard IMO. We the viewers should at least have a choice - or some say in the matter. And as far as I know, HD set top boxes and TVs could handle it, could they not?
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Old 23-04-2012, 08:36
Nigel Goodwin
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It would be nice if we the viewers were allowed to judge the benefits of higher frame rates - even if they had to do it at 720p/50. Trouble is that we've never had the chance and that makes me angry because many people would prefer natively recorded 720p/50 to 1080i/p25 (frames).
You had the chance, but you didn't take advantage of it - 720P50 was transmitted during the original HD testing phase, and compared with 1080i50. Apparently the ovewhelming opinion was that 1080i50 was better. I also don't think there were any (or at least many) natively recorded 720P50 sources.

I do think it's really discussion with no point though, the crippled bitrates used make it all a pretty moot point.
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Old 23-04-2012, 10:34
DragonQ
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Quite a few US stations use 720p/60 (especially sports channels) but I don't know if most of their footage is natively in this format or detinerlaced from 1080i/30 sources.

Ideally everything would be filmed in 1080p/60 or 1080p/50, allowing simple downconversion to both commonly used formats.
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Old 23-04-2012, 14:09
icstm
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US cable channels are split.
I think NBC/CBS use 1080i 30f and FOX/ABC use 720p/60f
Shows like Lost and 24 were shot in 24f, a nice multiple of 60 (2.5).
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Old 27-04-2012, 20:40
ab48uk
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James Cameron has said some things that I agree with, but surprisingly the industry doesn't choose to follow him. He wanted 48fps as standard the other year, yet everything is still 24fps. He's right about 24fps stutter being even more objectionable with 3D, but Hollywood is in no hurry to make all its films look like smooth high resolution video.

Cheers,
David.
Well it seems Peter Jackson at least was keen - and has shot 'The Hobbit' at 48fps. But most preview audiences didn't like the end result.

http://www.slashgear.com/the-hobbit-...axed-25224697/
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Old 27-04-2012, 22:22
mwardy
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Well it seems Peter Jackson at least was keen - and has shot 'The Hobbit' at 48fps. But most preview audiences didn't like the end result.

http://www.slashgear.com/the-hobbit-...axed-25224697/
Well, I hope they aren't put off by a single screening. Especially as most of it is according to that article already shot.

Really, what's not to like about films getting closer to reality as the eye perceives it? They should have gone for 60 fps a la Showscan or, more ideally and in film friendly style, 72 fps.

The only thing that stands in the way is an admittedly monumental cultural association between low framerates and 'quality'. I hope they follow through with Jackson's attempt to try to change this habit. Not going to be easy, but as the youth of today are used to constant technological change it might happen...
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Old 27-04-2012, 22:42
jzee
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Really, what's not to like about films getting closer to reality as the eye perceives it? They should have gone for 60 fps a la Showscan or, more ideally and in film friendly style, 72 fps.
Maybe because people prefer films to have a dreamlike quality, and 48fps progressive is too lifelike?
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Old 28-04-2012, 12:07
mwardy
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Maybe because people prefer films to have a dreamlike quality, and 48fps progressive is too lifelike?
Interesting. The idea of low framerates being part of what makes cinema dreamlike hadn't occurred to me exactly. There is as you probably know a lot of theorising about the basic proposition that cinema and dreams share many qualities, and this would fit well.

But whatever it is, it is learned behaviour. If film had been high framerate for most of its existence we wouldn't have these deep seated associations, and blurs duing pans are just irritating. So people should stop it!
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Old 28-04-2012, 12:17
figrin_dan
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I think the only way I would pay to see The Hobbit is if it was 48fps 2D.
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Old 28-04-2012, 13:54
White-Knight
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I think the only way I would pay to see The Hobbit is if it was 48fps 2D.
96fps 3D for me.
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