GH1 - 24p in 60i Stream. Can someone explain STREAM/WRAPPER?

[Dave Mercer]

I've done some online searching but haven't got a handle on this one yet.

How does 24/25p in a 60i/50i stream/wrapper work. Are the progressive frames halved into 2 fields and written/stored as 60i/50i (adding pulldown with the NTSC framerate)?

Is motion any smoother or does that not play into it as the 2 fields are recorded at the same point in time?

Sorry for the newbie question.

[Chris Medico]

The wikipedia article for pulldown will get you most of the way:

Telecine - Wikipedia, the free encyclopedia

[Dave Mercer]

Thanks Chris.

I understand the concept of pulldown removal.

What I'm curious about is how 25p in a 50i stream works (I record in PAL framerates). It's not real 50i like the GH2 (with 25 frames divided into 2 fields, each representing a different moment in time). So are each of the frames halved into 2 fields? Does this affect how motion is seen on an interlaced TV (making it less studdery)?

[Chris Medico]

Sorry about that. I should have been more specific about what I was recommending you check out. Part of the page there has info directly relevant to your questions. Since you stated you were a newbie I didn't want to assume too much.

The wiki page under the section "Frame Rate Differences" shows how a frame of film (progressive media) is divided into 2 fields and pull-down added so it can be embedded into an interlaced stream. Depending on whether you are shooting PAL or NTSC it shows the differences in pulldown for the different standards. That is the answer to one of your questions. Yes, progressive material is line divided and then treated (stream wise) as interlaced material for transmission. If everything works correctly the content flag identifying the material as progressive is set so this fields can be correctly recombined when the images are displayed.

As far as the question whether converting progressive to interlaced increases judder the answer that I can give is that I've not noticed an increase of judder on modern HDTVs.

BUT

Modern TVs have the ability to read the content flags embedded in the stream and know if the source material was derived from progressive and/or if pulldown needs to be removed. If so the display will correct any of this stuff so the material is displayed properly. I have noticed a good bit of judder on older tube type TVs that lack any signal processing for pulldown removal or progressive display.

[William Hohauser]

Originally Posted by Dave Mercer

Thanks Chris.

I understand the concept of pulldown removal.

What I'm curious about is how 25p in a 50i stream works (I record in PAL framerates). It's not real 50i like the GH2 (with 25 frames divided into 2 fields, each representing a different moment in time). So are each of the frames halved into 2 fields? Does this affect how motion is seen on an interlaced TV (making it less studdery)?

It should look identical to 25p played on a progressive monitor. Splitting the progressive frame into fields is invisible for a playing file. Any motion artifacts (judder) are the result of shooting in 25p which is essentially half the frame rate of 50 interlaced. This is why sports are usually shot with interlaced equipment. The motion is clearer although each frame is half the resolution of the signal.

[Dave Mercer]

Thanks guys for your help.

I have to admit though that I'm still a little confused.

If you're able to bear with me, what's the difference between "25p wrapped in 50i" footage captured by the GH1 and true "50i" footage captured by the GH2? If 2:2 pulldown is added to the GH1's 25p footage shouldn't the results be as smooth looking as the true 50i footage captured by the GH2 (considering both contain 25 full frames - and both involve shooting at 1/50 sec shutter speed).

You see i'd actually prefer to be shooting 50i on my next project as it will be more run and gun style and I don't want too much jerkiness. Plus, my delivery format is 50i (for HD broadcast).

Thanks for your patience!

[Dave Mercer]

I think I found an answer to my question on another forum:

"In normal interlaced PAL footage (50i) the camera shoots one field every 1/50 second. Basically the camera shoot field A followed by field B then another field A followed by B etc. Field A and B together makes the full frame (25 frames each second)

In progressive PAL footage (25P) the camera does exactly the same thing as in interlaced, the only difference being that it captures both A and B fields at the exact same time instead of first A then B. You could say it shoots 25 frames per second which then are divided into two fields (50 fields per second) in order to be compatible with the PAL video standard."

So since the the fields are captured sequentially in native 50i, whereas they're captured at the same time with 25p wrapped in 50i, the motion of true 50i should be a lot smoother. Hmmm ....

[Jeff Harper]

I'm not sure why you would not just shoot in 50i if that is your end product?

The jerkiness of 24p or 25p is not the result of the the footage being inherently jerky, it is the result of not using proper camera technique to fit the frame rate. If the footage is jerky it was not shot correctly. If it is smooth, the proper camera technique was used.

Yes it will still be jerky, of course whether it is is a wrapper or not, if you do not shoot properly.

When the FX1000 came out everyone was trying the 24p or 30p in a 60i wrapper, and then complaining how jerky it was. The wrapper's purpose, I don't believe is to smooth it out, but to make it editible for amateurs. I could be wrong on that, but that's my suspicion.

Anyway, for broadcast purposes your focus should be on minimizing issues,IMO. Just my 2 Cents, again.

[Jeff Harper]

What you are hoping for Dave is 25p footage that doesn't have the "negative" characteristics of 25p, or less of it, and that when it's in a 60i stream it should be smoother.

What I'm trying to say that the only way to "smooth" it out is to take away the very same characteristics that you need for the film effect. If you need smooth footage but are shooting documentary style, or run and gun style, then 25p is a poor choice regardless and it should be skipped. I think I'm on track here, but someone correct me wherever I'm mistaken.

[Dave Mercer]

Yeah Jeff you've got it nailed. So far I've mainly used the GH13 locked off (except when I'm using it to film family and friends). I've used both native 25p and 25p in 50i wrapper, and to be honest couldn't tell the difference looking on my 21" LCD.

I kinda assumed 25p in a 50i wrapper consisted of 2 fields recorded in the same instant, and so the same rules of filming in 25p applied to 25p in a 50i wrapper. I just wanted to double check.

Like you advised, I would certainly use 50i to film run and gun stuff but of course the GH13 doesn't give me that option. And I would have bought a GH2 but I need the ability to switch from NTSC to PAL, so it doesn't work. Let's see what Vitally comes up with eh?

While I appreciate that many people use the GH1/2 etc for the film look, 25p motion judder is not the biggest turn on for me. What i do appreciate about the GH1 for the work I do is the tiny size, the sharpness, the exposure latitude, the higher resolution of progressive frames, and of course the shallow dof.

Bring on 1080p50!!

[Jeff Harper]

I'm using 720 60p, which doesn't have the resolution of 1080, of course, but like you I have different cams with different abilities, so I'm kind of stuck with 720p. Not that I'm complaining, I love 720p, it is SO easy to work with, and it converts to SD widescreen perfectly from Vegas' timeline, where 1080 I need to resize and it just gets more complicated. So 720 60p is truly perfect for me anyway, really. And of course for the web 720 is optimal, as Vimeo only does 720 anyway for HD, so I am fortunate is a way to be forced into 720p.

[Corey Graham]

Originally Posted by Dave Mercer

While I appreciate that many people use the GH1/2 etc for the film look, 25p motion judder is not the biggest turn on for me. What i do appreciate about the GH1 for the work I do is the tiny size, the sharpness, the exposure latitude, the higher resolution of progressive frames, and of course the shallow dof.

That's the reason I finally decided to not shoot 24p. It's so jittery, especially when I watch it alongside 30/60p. And I really don't see it sticking around much longer, as it by no means gives the instant "film look," and seems to only be around so that people can say that they shoot in 24p. I was only considering it because of the GH1's inability to do 1080/30p. I was even ready to go through pulldown removal on my unhackable GH1.

Originally Posted by Jeff Harper

So 720 60p is truly perfect for me anyway, really. And of course for the web 720 is optimal, as Vimeo only does 720 anyway for HD, so I am fortunate is a way to be forced into 720p.

I love 720p, and am grateful that you helped me come to terms with it :)

Now that I've been working with it for a while, it has really grown on me. The only thing that suffers are screen grabs for the packaging art. But I manage to work with them enough that it's not really an issue.

[Dave Mercer]

I've never tried 720p50 as I deliver in 1080 for HD broadcast. I need to check out if the sacrifice in resolution is worth it for the smoothness.

What patch do you use for 720p60 Jeff?

[Jeff Harper]

Is the final prouct broadcast in 1080? Here some networks broadcast in 720p.

[Dave Mercer]

Yup. 1080 50i.