Shooting 60P for 24P

Boz

Boz

Well-known member
So, I'm hearing how much the 720P mode rules over the 1080P mode on the GH1. That's fine since I was always planning to work at 720P regardless. I also hear that you can drop 60P footage into a 24P timeline and it pretty much works seamlessly - also good news. But this brings up a couple of questions:


  • If you shoot 60P with the intention of converting (or dropping) to 24fps, wouldn't the slowest shutter speed available be 1/60th?
  • Wouldn't 1/60th be the shutter speed be the desired speed to shoot at, not 1/120th?
The way I'm figuring this is to look at 1 frame of 24P footage. That is a single "photo" shot at 1/48th of a second. Now if you took a single frame of 60P footage and looked at that, wouldn't you want it to be as close to that 1/48 shutter speed as possible? Remember this is not a question of shooting 60P with the intention of using it as slow-mo footage at 24P, it's the intention to drop frames and watch it at 'normal' speed.

Any thoughts / guidance would be greatly appreciated.
 
I'm with you on this question Boz. Hopefully Kholi will eventually figure out the best settings for 60p meant for a 24p timeline.
 
I've gotta do a retest on the shutter speeds tomorrow. mostly to help myself decide why it's letting me select and shoot 720/60P with a 1/30, 1/40, 1/50 shutter speed and what it's actually DOING, or what it's NOT doing.

I'm pretty sure those are inaccurate shutter speeds in video mode and the camera just isn't changing anything.

I'll get to the bottom of it asap by doing some conversion tests up to 1/120.

You'd definitely want it to look as close to 1/48th as possible, though.
 
Kholi said:
You'd definitely want it to look as close to 1/48th as possible, though.
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Thanks. That is what was throwing me, since in 24p you would shoot 1/48 for a normal look, I was then thinking that for 60p you would use 1/120, but then if you are going for a 24p master in the end then would it look more like proper 24p with 1/60 or 1/50 shutter?

So when you drop these 720 60p clips into your 24p timeline are there any adjustments or extra rendering before you can play them back? I remember when you first mentioned this method that you stated it was necessary to turn off motion blending. Also, does this only work with FCP or will the other NLE's allow a nice filmic 24p to originate from 60p? Any more info on this 60p to 24p process would be greatly appreciated.
 
Kholi- It looks like when I record 720/60p with anything less than a 1/60th shutter, the camera records 30p inside of 60p- each frame is doubled. But when Its at 1/60th (or higher), 60 unique frames are recorded. Give it a try and confirm.
 
I would think one would shoot for a 180 degree shutter no matter what frame rate you choose. So @ 24p...it will be 1/48 and @ 60p it would be at 1/120. This would keep the blur consistent...right?
 
If you're shooting 60p to project at 24p, you want a 1/48 shutter, so that each frame is exposed for the same amount of time as if you were only shooting 24 fps. This is if you're dropping frames. Of course you can't have a 1/48 shutter when shooting 60p, so 1/60th would give you the max motion blur and the closest equivilent to shooting 24p.

If you're shooting 60p for a slow-mo effect, then you would use the 1/120th shutter to simulate a high speed film camera that is shooting at 60fps.

Motion blur is dependant solely on how much the object moves while the shutter is open. So in a situation where you're dropping frames to get 24p, but shooting 60p, to get the motion blur as if you were shooting 24p you'd use the same shutter you would be using if you were actually shooting 24p.

Clear as mud?
 
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hunter richards said:
Kholi- It looks like when I record 720/60p with anything less than a 1/60th shutter, the camera records 30p inside of 60p- each frame is doubled. But when Its at 1/60th (or higher), 60 unique frames are recorded. Give it a try and confirm.
Click to expand...

Damn that makes sense. I was wondering HOW it worked. Thanks man!

Did you try dropping the footage on the timeline and playing back? What's it look like?
 
Boz said:
Stu Maschwitz gave a great response to the shooting 60P for 24P question over on the Rebel's Guide Forum:

http://rebelsguide.com/forum/viewtopic.php?t=2603
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He also recommends that it is still better to shoot in real 24p if possible.

You guys are correct. Since you'd want each frame to have as close to 1/48th shutter blur as possible, and time is still 1:1 from record to playback, 1/60 would be the best you could do.

HOWEVER, be aware that when you convert 60p to 24p like this, you do so by dropping frames. And not a consistent number of frames — you'll drop one, keep one, drop 2, keep 1, drop 1, keep one, drop 2, and so on:

X _ X _ _ X _ X _ _ X _ X _ _ X _ X _ _ X _ X _ _ X _ X _ _ X _ X _ _ X _ X _ _ X _ X _ _ X _ X _ _ X _ X _ _ X _ X _ _

(that's 24 X's out of 60 characters)

Although it can be surprising how well this can work (it's how we converted 60i to 24p before there were 24p cameras), it's no substitute for shooting actual 24p. If you have 24p available to you, then use it!

-Stu
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But as Kholi said, he can't tell the difference from doing this with his GH1 footage. I think the bottom line is if it looks right then it is a viable option. Same thing with compression, if it looks good one in motion, then don't worry so much if it doesn't look perfect when you scrutinize a single frame grab.
 
I'll get some more eyes on the 60 to 24.

Also still have some more shutter tests to do with it.

It's quite possible that I'm wrong and my eyes are busted.
 
Thanks for all the testing, Knoli, it's much appreciated. A pretty easy way to test for 60P to 24P smoothness would be to shoot some highway or freeway footage of cars moving across frame at consistent speeds. I would think any sort of jutter or weird frame skipping would show up pretty clearly in such a case. Just a suggestion.
 
You see the pulldown cadence to get 24p out of 60p every day - it's how 24p movies are reproduced on a 60i TV tube.

The VariCam also produces 24p with a pulldown over 60p. And nobody ever complained about it.
 
Well, consider me 'complaining' then, because I just did a test with SonicState's footage (I hope you don't mind Sam!), and unlike Kholi I can definitely see a difference between this and regular 24P:

http://www.vimeo.com/4548905

Notice the 'pulsing' as people walk? That's the conversion pattern as explained by Stu in the above thread. I find it highly noticable and not very pleasant to look at.

Edit: One more thing, this is not an artifact of Vimeo. My conversion footage looks the same. I believe you can download it from the link provided above to see for yourself.
 
Yes, I can see it clearly, too. Strange, it's very strong. Almost looks like a 30p to 24p conversion. But I personally don't have any experience with this kind of pulldown, so I can't judge it. Just wonder how the VariCam manages the trick.
 
Boz said:
Well, consider me 'complaining' then, because I just did a test with SonicState's footage (I hope you don't mind Sam!), and unlike Kholi I can definitely see a difference between this and regular 24P:

http://www.vimeo.com/4548905

Notice the 'pulsing' as people walk? That's the conversion pattern as explained by Stu in the above thread. I find it highly noticable and not very pleasant to look at.

Edit: One more thing, this is not an artifact of Vimeo. My conversion footage looks the same. I believe you can download it from the link provided above to see for yourself.
Click to expand...


Boz, that footage isn't 60P, it's 30P. When the shutter dips below 60 in 720P mode it shifts into 30P mode. That's why it looks FUNKY.
 
That must be the reason! It looked too jerky for a 60p to 24p conversion. By the way I found a quote from Barry Green where he explains how the VariCam works:

"For 24P, it runs the CCD at 24Hz, giving true 24p capture. Each frame gets written to tape either two or three times, alternatingly, so it does a 2:3 pattern on tape. Those frames can be removed when editing; FCP-HD can extract the "active" frames, ignoring the duplicate frames, leaving a 40mbps pure 24p file on disk. This system is necessary because the tape drive must, by definition of the format, record 60 frames per second."

So, though much better than 30p to 24p, a conventional 60p to 24p conversion might no be THAT smooth as it does a VariCam...
 
I'll have a lot of 60 to 24P footage up tonight. Random stuff but then people can judge for themselves.
 
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