Why I would want to shoot in a different frame rate?

This is the biggest mystery to me.

I hear all the time of people shooting in 24p, 23.97, 30p, 29.97, 25p, 50p, 60i....etc. I'm having a hard time understanding all of this. I looked on the FAQ, and it's still a bit of a mystery to me...it's a little over-technical for me to understand at this point...so I'm going to try to ask this as a simple person would ask.

Why would I want to shoot in a different frame rate than 29.97 or 60i? Anything that I have worked with that were other than that has looked jittery. I understand that going to 24p (whether or not that's true 24p) is trying to get the film look. But what I've seen doesn't look very good...it's still jumpy (stuttery, jittery, bouncy, strobey...whatever).

Most well done Hollywood DVDs don't have this jumpy look...it's a lot more subtle.

If my output is going to DVD, and is going to be watched on normal TVs...why would I want to use a different frame rate...since I'm not going to actual film or doing any online versions?

I think what I really need is a dummies guide...can anybody explain this to me or refer me to someplace where this can be explained to a "dummy" like me?

Thanks!
Casey Petersen

Hmm. It's a good question, and a challenging one to answer.

The short version is that you want to shoot 24p. I'm just gonna cut straight to that so there's no confusion. The frame rate of the motion picture arts is 24p, and 24p is the frame rate you want to use. Why? Just look at something shot in 60i (like sports, or live television news) and compare the motion quality to something shot at 24p (like practically anything else in the world). The difference is self-evident.

Three quick notes: First, I'm taking 24p and 23.976p as synonyms. Actual film runs at 24 frames per second, for engineering reasons the corresponding video rate has to be 23.976. So assume I mean "23.976" when I say 24p in the context of video instead of actual celluloid film.

Second, if you're unhappy with the motion quality of 24p material, that's probably because you shot it wrong. A discussion of shutter angles and panning speeds is a bit outside the scope of this post, but suffice to say that if you like the motion quality of professionally shot 24p stuff, your problem clearly is not with 24p.

Third, comparing 24p to 60i is obviously only valid if you live in an NTSC country. In PAL-land, they're actually a bit better off, because 25p-over-50i is a not-entirely-terrible approximation of 24p.

So really the question becomes, why would you ever want to shoot anything other than 24p? Obviously you'd shoot another frame rate if you were shooting off-speed; that's what shooting off-speed means. But when you shoot off-speed, you run the camera at some other frame rate, but you still play back at 24. That's how slow motion works: you record more frames per second, but play back at the normal rate, making a "second" longer than a second.

Let's say you wanted to shoot a shot at 48 frames per second for slow-mo. No problem. You just dial your camera's frame rate to 48 and ? discover that your camera can't shoot 48. At least, that's probably what happens, since relatively few video cameras are capable of shooting off-speed. Does that mean you can't shoot off-speed? Absolutely not. You could shoot 30p if your camera supported it, for a very slight 125% time stretch. Or with a little more trickery, you could shoot 60i for a more dramatic 250% time stretch. The technique for pulling this off varies from workflow to workflow, but the theory and some praxis are covered in Stu's book The DV Rebel's Guide.

Why else would you choose to shoot something other than 24p? Well, you could do it for artistic, creative reasons. I can't remember which one it was now, but some popular one-hour drama some years back did a gag episode, the conceit of which was that a film crew was there filming a documentary. The episode in question mixed normal footage (i.e., 24p) with 60i stuff that was supposed to be from the documentary camera's point of view. It was gimmicky, but effective. Really effective, actually, because the motion quality of video is so radically different from 24p, intercutting between them was really effective. It's not a trick that would work on any old show, but it was used there to great effect. (It wasn't just the frame rate; they also used some really, really clever lighting set-ups that worked for both cameras in different ways, if I'm remembering correctly. It was neat.)

So that's two reasons: 1. You might shoot 60i if you're doing a "rebel slowmo." 2. You might shoot 60i if you're, for artistic reasons, deliberately trying to make your shot look like crappy videotape.

Other than that ? I guess the only other reason I can think of is technical. If you're shooting something where you really need the higher frame rate and reduced motion blur of video, you can shoot 60i. I'm thinking now of something like ? um ? a flying saucer lands in your back yard and you want proof. If I were shooting something like that, I'd want the highest frame rate and the sharpest picture I could get, and to hell with the aesthetics. But that's obviously not creative cinematography. That's documentary cinematography, and it's part of the reason why (with a few exceptions) ENG crews still shoot 60i as well.

So short answer? Shoot 24p, no exceptions. Once you've got enough experience to recognize those situations where you really do want to shoot another frame rate (which won't take long; this isn't tensor calculus or anything) you'll know when, why and how to achieve different looks.

THANK YOU JEFF for your thorough explanation!

It is making more sense to me...mostly

Does the fact that I'm going back down to DVD have any effect on this situation?

Also...I'm shooting with a Sony Z1U for everything, I can't change it from 60i. It does have this fake Cineframe mode, though. We just got a Canon 7D yesterday and are planning on integrating footage between both cameras in future projects.

Any thoughts on any of this?

Thanks!!!
Casey

>This is the biggest mystery to me.

It started with electricity. Some countries chose to go with 50 Hz, some decided to go with 60Hz. Not a biggie, but when they developed technology for broadcast video, the countries that were on 50 Hz eventually went with PAL (50 fields a second), and the ones on 60 Hz, went with NTSC (60 fields a second).

The ones that went on 60 Hz ended up with a whole mish mash of frame rates and frame sizes that from the outset seem to defy logic. Well, I guess it was bad luck, but the nature of video is to ensure backward compatibility with technology of the previous generation, so as to allow faster market adoption. What happened, is that when they came out with color TV for NTSC, they had to slow down the picture by 0.01% to prevent the chroma subcarrier from interfering with the sound information. Which leads us to 29.97 fps and drop frame timecode.

And of course, later when we moved onto digital video compression, us PAL folks got lucky and we kept the same frame size for digital compressed formats. DCT based compression requires pixel resolution to be in multiples of 16. 576 was divisible by 16, but 486 wasn't, so along came the birth of the DV frame size- 720x480. We simply discarded those lines. Who cares? Nobody sees it anyway. But that's besides the point. But the point is that more standards are created, which isn't necessarily a good thing.

Then along came our saviour- HD. Well, we thought that HD would save us from having yet more standards, and it could be our chance to start anew, but HD brought along a large committee to the party! And as committees go, well, they drafted out not one but two HD frame sizes to bicker about- 720p and 1080i. And lobbyists for the 720p standard pushed for the the end of the interlacing, which was really quite a royal pain to explain to non-video people and besides, the demise of CRT TVs for HD meant that nobody watches interlaced TV in HD anyway. With 720p, you can broadcast in 50 or 60 full frames per second, whereas 1080p50/60 would take up too much storage and bandwidth. Not to mention p25/24 is not really good for sports and fast movement. Hence 720p is broadcasted exclusively in 50 or 60 (I think it's 59.94 actually) progressive frames a second.

Anyway 1080 eventually won the war (read: is winning the war), as it provided better still resolution than 720p. We still kept the different frame rates, partly for backward compatibility, as well as to allow a smoother transition of SD material to HD and vice versa.

Of course, besides introducing a whole bunch of formats, HD also introduced a lot of jargons, which is extremely confusing for the non-initiated. 1080i25 is essentially the same thing as 1080i50. 1080i60 is the same thing as 1080i29.97.

So that's kind of the story of the thousand and one formats of broadcast video and how the different frame rates came about.



www.strypesinpost.com

Quote

I'm shooting with a Sony Z1U for everything?Any thoughts on any of this?

Nope. I've never seen footage from that camera. Use your own eyeballs. They're the best measuring tool you have.

Strypes, I want you to come to my apartment and read me bedtime stories. Can I hear the one about the Passing of the Great and Powerful Optical Soundtrack and the Rise of Super35?

Casey:

I shot with the Z1U before the HVX200 came out. It was the first reliable, affordable HDV camera available. I shot a lot with it, like 20 or 30 projects in one year. Here is the deal with the Z1U. Don't use Sony's lame Cine mode, it is a total hack that uses an inconsistent cadence. For this reason, it doesn't look like 24p, it looks weird. Think of the Z1U ONLY as a 60i camera, because that is what it is. I shot a lot of beautiful scenic footage of Monument Valley with the Z1U that was used on a piece I did for the Warner Bros. DVD release of "Fort Apache" called "Monument Valley: John Ford Country". For certain things, the Z1U is a sweet camera.

The Z1U is excellent for exteriors. For interiors, it requires a lot of light to look good. A really high level of light to even correctly expose the image, it is really slow, which is bad for modern, lazy shooters who want to shoot in underexposed low light levels constantly. It takes a lot more lighting skill to effectively light for slow cameras, ask any 35mm adapter user.

The audio is so-so. The menus and navigation, really bizarre. The random cadence that they use in their fake cine mode is also really random and terrible. You can always shoot 60i and turn it into 24p, that would look better than their lame Cine mode.

Dan

If the ZU1 24p is your only reference to 24p...then you haven't seen GOOD 24p...


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great post
i've learned a lot and eventually forget, but I did bookmarked the page so I can come back...
I have a CAnon xh-a1, how good is for 24p????

SO I can start a tape with 60i then switch to 24p? Does FCP recognize this automatically?


thanks

Do not mix formats. Switch tapes. Do not mix formats unless you have to and have a good reason for it.

There is nothing magically about 24fps. There is nothing magical about the motion picture frame rate. It was chosen because it was the lowest frame rate that could be used with optical sound, and therefore expended the least amount of film. 24fps has more to do with greed than aesthetics.

Wow! Great replies! I suppose I haven't seen real 24p before, come to think about it. I've never used the Cineframe mode...I think it looks ridiculous, too.

How would you recommend going from 60i to 24p...Compressor, right?


Thanks!!!

Like someone told you before don't mix frame rates.

If you have to mix Z1 with HX A1 @24 f and or 7D @ 24p the best way is to convert the A1 and 7D to 60i before editing.
I have the FX1 that is similar to the Z1 and I shoot a lot at the fake 30 that looks ok. I also own the Canon A1 and when I mix them I shoot both 60i to avoid all the extra processing and different looks in one video.
The A1 does a good 24f, so if you want to see what a good 24p or f looks compared to 60i the A1 is a good camera to do it.

God Bless,

Douglas Villalba
director/cinematographer/editor
Miami, Florida

[www.DouglasVillalba.info]
[www.youtube.com]
[vimeo.com]

Yep, I definitely did that last time...I used stills, Z1U footage, and 5DMKII video in the same edit...very creative/artistic edit, so it was all good.

We have a shoot this evening...a low buck, low pressure thing. I'm shooting it with the Z1U in its entirety, and my boss is going to be shooting stills for the most part, but will also be doing some video with the 7D...mostly as an experiment. This isn't even going to be edited...they're getting a straight copy of my Z1 footage, and a DVDROM of the stills. We're planning on shooting the 7D at 30p.

We'll bring in a little bit of the Z1 footage and the 7D footage to play with and see how they look together.

How would you recommend converting the 7D footage?

Thanks!

PS...I never got an answer to my question about how using 24p footage is affected when going to DVD

>I never got an answer to my question about how using 24p footage is affected when going to DVD


24p (actually 23.976), will be encoded on the DVD as 24fps (23.976), the pulldown if needed, is added on playback. With this, you will encode less frames per second, allowing you fully utilize the bitrates.

On the other hand, you aren't actually shooting 24 fps. For tape based formats, a pulldown is always added. Pulldowns is basically adding a bunch of duplicate fields/frames to a 24 fps signal to make it 29.97 fps.

There are two different kinds of pulldown for most formats (except for 720p). You have your normal pulldown (24p), which is not designed to be as easily removed. And you have your advanced pulldown (24pA), which is designed to be removed on ingest.

This may seem confusing. But keep in mind that 24p is not necessarily 24 fps. 24p that comes from the camera would usually be 29.97 fps (24p with a pulldown). Actual 24fps (which is actually 23.976) would be notated as 24pN (native).

Basically the Z1 sounds like it shoots a half a**ed kind of 24p (woodstock speak for an inconsistent pulldown). I'm not sure if shooting 25p and conforming it to 23.98 would result in a better option, but obviously you would need to rethink your post workflow properly..

Yes, as Tom and everyone else mentioned, DO NOT mix your frame rates. You can't cut easily between shots with different frame rates, not to mention the conversion to get everything to work together would throw your workflow into a mess.



www.strypesinpost.com

I'm going to ignore the "I can shoot 60i and 24p on the same tape, right?" thing. That reveals such a fundamental lack of understanding of how videotape works that I don't even know where to begin.

But if we're going to talk about converting footage from one frame rate to another, or what "good 24p" means, then I'm gonna have to nerd it up a little bit.

Let's start by thinking about how a motion picture film camera works. Not because film is this awesome ideal to which all should aspire, but because of the simple fact that film came first, and as a consequence of mechanics and basic physics it had certain characteristics, and modern digital video largely tries to emulate those characteristics. So film is a good place to start figuring out how this stuff works.

A very simple film camera consists of only five pieces: a lens of some kind, an aperture for letting light in, the film itself, a motor or some other mechanism for pulling the film past the aperture, and a shutter that sits between the aperture and the film. It's this shutter that we need to pay special attention to right now.

If you're familiar with stills cameras, you probably have completely the wrong idea about how a motion picture camera's shutter works. In a stills camera, the shutter is some kind of metal window (there are various designs) that opens and closes to let in or keep out light. The longer you keep the shutter open, the more light comes in, and the more exposed your image is. If you're shooting a brightly lit scene, like in daylight, you'd keep the shutter open for a very short time, on the order of a hundredth of a second or less. If you're shooting with very little light, you'd keep the shutter open longer, for what's called a "longer exposure."

In other words, in stills photography the shutter is a tool the photographer uses for controlling the exposure, or overall brightness or darkness of the image.

Motion picture shutters work entirely differently, and thinking of a motion picture shutter as a tool for controlling exposure is a great way to make crappy looking footage. Instead, think of the motion picture shutter as a tool for controlling motion blur, or the overall motion quality of your footage. And what's more, think of it as a tool for advanced users only. Think of it as a dangerous tool, like a band saw or a stick of dynamite. It's got uses, but it requires careful training to use safely, and most people should stay the hell away from it unless they want to get maimed in a horrific workplace accident.

The simplest kind of motion picture shutter ? and the kind that's still in use in film cameras today ? is just a semicircular metal disc that sits between the aperture and the film. This disc rotates when the camera's running, blocking the light when the metal half is in front of the aperture and letting light in the rest of the time. We spin the shutter in sync with the motor that moves the film, such that when the film is advancing through the gate (that's movie jargon for the time when the film isn't sitting still) the shutter is blocking the aperture. In other words, the shutter makes a complete revolution exactly once per frame of film passed through the camera.

But wait. The shutter is only open ? that is, it's only letting light hit the film ? for half of its revolution. And it revolves once per frame of film, which is 24 times per second, but that means it's only actually open half that time. We run the film at a rate of 24 frames a second, but each frame is only exposed to light for 1/48th of a second. Because we have to use the "other 48th" to move the film from one frame to the next.

In stills photography, the amount of time the shutter is open is a variable. It can be half a second for a very long exposure, or a thousandth of a second for a very short exposure, or anything in between. In motion picture photography, the amount of time the shutter's open per frame is basically a constant, and it's basically always equal to half your frame rate, in seconds. I said "basically" there because it is possible to change the amount of time the shutter's open per frame. Remember how I described it as a half-disc made out of metal? It's actually a set of overlapping metal leaves. The leaves can be spread out to make the shutter cover more than half of its area, or they can be squeezed together to cover less than half of its area. This translates into either a shorter exposure time per frame, or a longer exposure time. In industry jargon, we call this using a "short shutter" or a "long shutter." The use of a short or long shutter is what I was talking about earlier when I described a dangerous tool that you have to be trained to use safely.

Yes, I'm going somewhere with all this; you guys need to be more patient.

You know what motion blur is, right? Motion blur is an artifact of the physics of photography. Imagine a magical camera that takes instantaneous pictures. Zero time elapses between the opening and closing of the shutter; you hit the button, and pop, you have an image of a single instant of time. Because no time elapses while the picture is being taken, it's not possible for anything to move while the picture's being taken. Everything in the picture is perfectly frozen.

Of course, no real camera could work that way. In a real camera, some time has to elapse between opening and closing the shutter, and during that time, the stuff in front of the camera can move. If something moves while it's being photographed, then the film records light from both where it was when the shutter opened, and where it was when the shutter closed, and every point along its path in between, which makes that object's image on film blurry. The amount of blur is proportional to the distance the object moves in the film plane during the exposure interval, which simply means that fast, close things are blurred more than distant, slow things. A technical explanation of motion blur actually gets really complicated, with vectors and angles and planar projections and all that stuff, but the truth is we all know motion blur when we see it, 'cause we've been looking at photographs all our lives.

Film, with its exposure time of 1/48th of a second, is actually quite blurry compared to conventional stills photography. And that's a good thing. What if you used that magical instantaneous camera to make a movie? Each frame would be a perfect, sharp still which, when played back with all the other frames, would look horrifically strobey and jittery. The illusion of continuous motion would be completely shattered; it'd look like a flipbook of stills, which is exactly what it'd be. It wouldn't look like motion at all.

So motion blur, rather than being something to avoid, is actually critically important to the illusion of continuous motion. The right amount of motion blur tricks the viewer into thinking he's seeing more frames per second than he really is. But it's a careful balance; too much or too little motion blur breaks the illusion.

Which is where the concept of a short shutter comes in. A short shutter is open for less than half the frame rate, and so records less motion blur. This can be (and has been) used to great effect by filmmakers who are trying to do something specific with it. A lot of the action sequences in both Saving Private Ryan and Gladiator were shot with a short shutter, which gives them a staccato, hyper-real look. When an artillery shell goes off during the D-Day sequence in the first reel of Ryan, you can see every chunk of dirt and particle of dust kicked up by it with perfect clarity, even though the film's not running in slow motion. This is because the short shutter reduced the motion blur in the scene, making everything seem sharper and more in-focus.

Of course, that doesn't mean a short shutter is better than a conventional 180° ? that's 1/48 at 24 fps ? shutter. If you shot two characters having a conversation with a short shutter, it'd look stuttery and wrong. In fact, of all the possible uses of a short shutter, almost all of them would result in footage that looks stuttery and wrong. Which is why I described it as a dangerous tool. If you aren't extremely careful with it, you can metaphorically cut your movie's arm off.

At this point, we finally get to video. The effective frame rate of video can be said to be (or rather, rounds off to) 30 fps. But video doesn't actually record frames; it records fields. So (glossing over some math here) we can say the effective shutter angle of a video camera recording an effective 30 frames per second is 180°, for a 1/60th-of-a-second exposure per effective frame. In other words, the motion blur, and overall motion quality, of 60i video is equivalent to a 1/60th shutter.

Obviously 1/60th is less than 1/48th, so if you shot 24-frame film with a 1/60th exposure per frame, you'd be shooting with a short shutter. Which means less motion blur, and a more staccato, jittery overall motion quality. And as explained above, that will almost always look wrong.

A whole hell of a lot of low-end video cameras include some-or-other kind of "24-ish" mode. Sometimes it's described as a "film look" mode, sometimes it's called "cinema something," but it's rarely ever actually called "24p." Even when it is, "24p" on a video camera doesn't necessarily mean you'll get the motion quality you'd expect. Because even if the frame rate is 24p, the shutter might not be 1/48. It might still be 1/60, which is equivalent to a short shutter, meaning you'll get the wrong amount of motion blur and end up with footage that looks bad and wrong.

So if you want to shoot at 24p ? and you do ? you should at some point pause and ask yourself, "Am I using a 180° shutter?" If the answer is no, fix it immediately. Because you want to be using a 180° shutter, period, end of paragraph. If your camera is recording 24 frames a second with a 1/60 shutter, you're doing it wrong. Unless you're doing it on purpose, in which case you're obviously not a total newbie, and you shouldn't be looking to this post for advice.

Now, how does allllllll this relate to converting frame rates? Easy: the shutter angle is effectively baked into your footage when it's recorded. If you shot 60i with a 180° shutter ? 1/60th, at an effective frame rate of 30 frames per second ? then each frame will have the motion blur that corresponds to 1/60th of a second. If you then convert that footage to 24, no matter how sophisticated you get with your convolution algorithms and stuff, you'll still only have the motion blur that corresponds to 1/60th. Which is the equivalent, more or less, of shooting 24p with a 1/60th shutter, which is a short shutter, which will make everything look staccato and jittery and bad and wrong.

Now, this is not true if you're conforming the frame rate. If you just change the rate at which footage plays back, then the shutter angle remains constant. Say you go out and shoot a bunch of stuff at 200 frames per second, for slow motion. You want to play it back at 24p, and when you do, you want the overall motion quality to "look right." That is, you want the footage to look like the scene actually happened at a much slower speed, and you just filmed it with a normal camera and normal shutter. Figuring out how to set that shot up requires a lot of complicated math, right? Wrong. Just use a 180° shutter, or 1/400 at 200 fps. Why? Because shutter angle is baked into the frame when it's recorded. If you shoot with a 180° shutter regardless of frame rate, the result will look like it was shot with a 180° shutter when played back at a different frame rate. (This is why professional cameras don't let you set the shutter speed or the shutter time, but rather let you dial in a shutter angle in degrees: because the shutter angle should remain constant regardless of the frame rate you're recording.)

This is why you can get away with the "rebel slowmo" technique I mentioned up-thread. If you shoot 60 frames per second with a 180°, or 1/120th, shutter, you can slow that footage down to 24 frames per second with a 250% time-stretch, and it'll look right (i.e., it will have the expected motion quality). If you shoot 60 fields per second with a 1/120 shutter, you can do the same thing, sacrificing half your vertical resolution for two and a half times the temporal resolution. As long as your shutter angle is 180°, you can shoot at whatever frame rate you want, and your footage will look right when played back at 24 fps.

Footage that was shot at 60i and [/i]converted[/i] ? not conformed ? to 24p will never look right in an absolute sense, because it will have the wrong motion quality. But it may look "situationally right" depending on what you're trying to do. And with optical flow retiming, it may look good enough to get away with, which is really all that counts in this business.

The key, as with any aspect of cinematography, is to

1. Know what you're trying to accomplish.

2. Have an eye that's at least basically trained to the point where you can recognize what you're trying to accomplish when you see it.

3. Understand the basic physics of cameras sufficiently to have some clue of what to change when what you wanted turns out not to be what you got.

Wow......to all that contributed I have learned a great deal with your posts. What was 'clear as mud' now is a helluva lot more understandable. Thanks very much.

>Yes, I'm going somewhere with all this; you guys need to be more patient.

I knew we shouldn't have let Jeff go to iTunesU...



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