Why does BBC film so much content at 25p

televisionuser

Active Member
I notice that BBC (and maybe some other channels) tend to film most of their content at 25fps. This looks okay with slow moving cinematic content, but with any fast camera movement 25fps gives me a headache. I feel like I need to switch on motion interpolation. 50i is a lot more comfortable and easier to track motion. Thankfully most sport is still 50i. When we moved to HD, surely we should have moved from 50i to 50p. 25p just seems like a step backwards to me.
 

brian s

Distinguished Member
I'm not an expert and I'm also not sure exactly what content you're referring to. The 25fps will be because of the PAL TV system. I don't have any issues with the BBC's output. I'm not aware of any great issue and I most certainly don't get any headaches.

Bri
 

televisionuser

Active Member
I'm referring to general TV broadcasts. 50hz is the PAL TV system. Both 50i and 25p are part of the PAL TV system, and before HDTV, everything was pretty much 50i. What I'm saying is that 50 interlaced frames looks a lot smoother than 25 full frames.
 

noiseboy72

Distinguished Member
I guess 25p looks a bit more filmic than 50i. The problem with 50p is the bandwidth to support. Moving from 720p 25 to 1080i 50 is not a big step, but 1080p 50 is.

Quite a lot of drama footage is shot on cameras that only support 25 or 30 fps, so this is another technical limitation. As you say, sports is still shot interlaced, as are studio productions, but news footage and indie productions are a different kettle of fish.

The BBC publish standards for programme making and these detail when interlaced or progressive is appropriate and in what format the output should be delivered in.
 

televisionuser

Active Member
The reason why I bring this up is that people complain about judder, and one of the main causes of this is poor motion resolution. If a movie is filmed at 25p and the camera pans too quickly, there aren't enough frames during the pan resulting in judder. There's nothing wrong with 25p/24p for cinematic content, as long as the camera movement is appropriate. But for anything with quick camera movements, 50i (1080i) would be more appropriate. Freeview HD probably doesn't support 50p?
I just think a lot of studios really should be filming in interlaced for most of their content. Otherwise, the solution to this is switching on motion interpolation in the TV settings. Anyway, this is all just my opinion.
 

doug_1986

Well-known Member
Hi there,

Pretty much the standard for the beeb is to film at 1080i50. This is changing now as everyone is moving to 4K (or moved), but when HD was being delivered, it was 1080i50. The HD delivery itself is 1080i50, so anything that was shot 25p ended up being converted to PsF.

Of course there are some differences, such as if you're shooting on a GoPro or a second camera, and now with 4k and 8k it's all a little different.

(I used to be a technician in the Beeb's Post Production)
 

Clem_Dye

Distinguished Member
I thought that for Freeview, GOP came into play, or is it not relevant here? BBC HD picture will change, depending on the GOP, from 1080i50 to 1080p50.
 

doug_1986

Well-known Member
Perhaps, but I'm not sure about broadcast itself. All I know of is the actual acquisition, and the file that's delivered to channel. OP asked why the Beeb film at 25p, when actually they usually don't
 

noiseboy72

Distinguished Member
Perhaps, but I'm not sure about broadcast itself. All I know of is the actual acquisition, and the file that's delivered to channel. OP asked why the Beeb film at 25p, when actually they usually don't
They might well film at 25p, but final edit and master should be 50i. The interlacing and any transcoding will be done at that point, probably also running legal colour checks and anti-strobing.
 

doug_1986

Well-known Member
They might well film at 25p, but final edit and master should be 50i. The interlacing and any transcoding will be done at that point, probably also running legal colour checks and anti-strobing.

But this is what I'm saying, most filming is done at 1080i50. Antiques Roadshow, Flog-It, Bargain Hunt, One Show, CBBC shows ,etc etc. Of course there are exceptions, such as drama and natural history, but the vast majority is 50i

Anti Strobing is known as a Harding Test and is run during Tech Review, and legal colour checks aren't really done - anything going through a grade will come out legal. Otherwise your Colourist is very bad.
 
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noiseboy72

Distinguished Member
A mate of mine runs Vivid Broadcast - which supply the pop up PPUs for Antiques Roadshow. As you say, anything mainstream should be fine, but some of the stuff that comes out of indies can be appalling and shot at a variety of rates and badly transcoded in the edit. I know that with digital production workflows illegal colours shouldn't happen any more, but my experience is that they do from time to time.

I was working on a shoot that involved a lot of people wearing hi-viz jackets under really bright LED warehouse lighting. We suggested they use some jackets we had that were not quite so dazzling as we had washed them with a slight dye tint and replaced the silver strips with grey, but they didn't have the logo they wanted to show, so instead they spent hours (days possibly) trying to balance the shots in the edit, as the fluorescent yellow was clipping the colour channels and causing all sorts of weird effects!
 

Nutty667

Active Member
I know what you mean. Its the "film" effect they add to shots to make them look cinematic.
The channel is 50i, but they post process shots to make it look like 24p. You can spot it on any arty show with nice visuals like Gardeners World. Watch the panning shots, its juddery as anything.

This has driven me insane for many years, I'd much rather see smooth panning like in sports, but too many tv show editors think juddery is artistic like in cinema.
 

doug_1986

Well-known Member
I know what you mean. Its the "film" effect they add to shots to make them look cinematic.
The channel is 50i, but they post process shots to make it look like 24p. You can spot it on any arty show with nice visuals like Gardeners World. Watch the panning shots, its juddery as anything.

This has driven me insane for many years, I'd much rather see smooth panning like in sports, but too many tv show editors think juddery is artistic like in cinema.

I've edited Gardner's World and have cut for all of the RHS Flower Shows.

All were shot and delivered 1080i50. Please, don't blame us!
 
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Nutty667

Active Member
I've edited Gardner's World and have cut for all of the RHS Flower Shows.

All were shot and delivered 1080i50. Don't blame us please.
Then why are the panning shots often soo jerky and juddery, when in live action shows camera movement is very smooth?
It's not just Gardeners World, it's in loads of other shows, not just BBC. James Martin's Saturday Morning show does it as well, the movement is juddery, it doesn't look like normal 50i.

Take Gardeners World, Easter special. At 22:13, there are some shots of yellow flowers panning on black backgrounds, and the movement is not smooth. It judders.
 
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noiseboy72

Distinguished Member
Might be worth checking your TV settings, as I've just looked at a recording of Gardener's World and it's smooth as.

In some cases, TVs will change modes based upon content and this can cause judder. A typical example would be scrolling credits - where you will see them judder for a second before the TV works out they should be scrolling smoothly.
 

Nutty667

Active Member
All motion settings are off on my telly, and my TV isn't new enough to do anything that complex. I was just looking at it on my desktop through iPlayer and it's still visible there.
The horizontal panning shots in Nick's garden on that show as well. All the vertical lines in the garden, wall edges, fences etc.. judder across the screen, they don't move smoothly as if it looked like normal live 50i.
Next time I see it on telly, I'll rewind it and video it.
 

doug_1986

Well-known Member
I quite like James Martin's Saturday show and I must say I've never noticed it. I'll keep an eye out next time.

iPlayer is a different beast all together, with the show having gone through varying levels of compression to get it to you. The AS11 is the file that's delivered to channel, and it'll be very smooth on there. That's 50gb /hour though, so clearly some further compression to get it to you is needed!

Exactly what happens between the delivery of the AS11 and it arriving on your box is, I'm afraid, beyond me.

If you'd like to have a little read, the technical delivery standards for the BBC are available here - Technical requirements.

If you follow that link, there is then a further link to the BBC specific technical delivery standards document on Dropbox, where it confirms that HD content must be acquired, post-produced and delivered at 25 frames per second (50 fields) interlaced.

And you'll just have to take my word that we're not slapping de-interlacing filters over everything in the offline!
 
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Nutty667

Active Member
I'll take your word for it, but Charlie Brooker did a show not long ago showing the various frame-rates used in TV to get different effects. Otherwise all the shows would look like live TV. Was he talking nonsense, and that's never used on TV ?

It definitely feel's like a post production thing. Just look on Saturday morning. Saturday Kitchen on BBC, live, smooth. ITV, James Martin pre-recorded, juddery cinema motion type feel.

There's definitely a difference, where that is coming from I'm not sure.
 

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