Apart from the $70,000 VariCam, the HVX200 is the first and only camera on the market that provides for variable-frame-rate shooting.  This is probably one of the most exciting features of the new HVX200, and certainly one of the most powerful features.  And it’s far more capable than most users realize at first glance – the variable frame rates provide you with unprecedented creative choices at this price point.

When talking about variable frame rates, we’ll limit this discussion to the high-definition 720p mode.  In 720p the HVX200 provides almost a dozen different frame rates to select from.  In 1080 or 480 mode there’s even a small provision to shoot with some different frame rates: there are three to choose from (24p/30p/60i), although it’s possible to simulate even more, specifically 6p, 8p, 12p and 15p, but we’ll leave that for another article.

Focusing on 720p, there are 11 different frame rates to choose.  In the US/60Hz model, those frame rates are 12, 18, 20, 22, 24, 26, 30, 32, 36, 48, and 60 frames per second.  In the European/50Hz model the frame rates are a little different; they include 12, 18, 20, 23, 25, 27, 30, 32, 36, 48, and 50 frames per second.  Since the frame rates are so similar, for the rest of this article we’ll primarily stick to the 60Hz frame rates for illustrative examples.

Why so many choices, and when and why would you use them?  The frame rates chosen for the HVX200 have been taken from the most popular frame rates on the VariCam.  The VariCam is actually capable of choosing any single individual frame rate between 4fps and 60fps, in 1fps increments. The Varicam is also capable of ramping framerates during shooting. On the HVX200, Panasonic has provided a select group of the by-far most popular frame rates, each suitable for a certain specific effect (although, of course, creative users will find other ways to take advantage of the choices offered), and you cannot ramp framerates during shooting, you must stop recording to change the framerates.

To start with understanding why variable frame rates even matter, let’s reference back to how film gets shot.  In film, slow motion is shot by running the camera at a faster frame rate.  Film normally runs at 24 frames per second (fps), but for slow motion the cameraman might shoot it at something like 48 fps.  When those 48 frames are played back at the 24 fps speed, it’ll take twice as long to play back, so everything will be moving at half speed, giving that superb film-style slow-motion look.  Shooting at a faster frame rate is called “overcranking,” because in the early days cinematographers would actually crank the film faster.  Similarly, shooting at a slower-than-normal frame rate results in a “fast motion” effect – think of the Keystone Kops or an old Charlie Chaplin movie and you’ll get the idea.  If you only shoot 12 frames in a second, but you play those frames back at the 24fps speed, it’ll only take ½ second to play back action that took a full second to record – accordingly, the motion will be twice as fast as normal.  This is referred to as “undercranking.”

Using actual overcranking and undercranking can yield dramatically smoother, superior off-speed effects in your productions.  Prior to the introduction of genuine over/undercrank, video shooters had to try to synthesize slow motion effects in their nonlinear editors, and this leads to frames being blended together, footage being de-interlaced, new frames being interpolated, and all sorts of other compromises that resulted in lower-quality footage and a less-than-filmlike slow motion experience.  With the true overcranking and undercranking potential of the HVX200, you no longer have to settle for those types of compromises; now you can shoot genuine frame-accurate film-style slow motion effects (or fast-motion effects).

We’ll offer some examples of what each frame rate is useful for, and ways that you could use them.  This is not by any means an exhaustive list, there are likely many, many more uses where each frame rate could be used, but this listing will give you a basic overview.  Each of the choices listed below assumes that you’re going to be playing back the footage at the film-standard rate of 24 fps (or 25fps for the European/50Hz version).

          Framerate Guide

For an example of what all these different frame rates look like, we put together a composite of some juggling shot at each of the frame rates into a 1280x720 high-definition Windows Media file.  Take a look at how the different frame rates look here:

Grasping all the creative possibilities that this wide array of frame rates gives you can be a little intimidating at first.  So it’s probably unfair of me to thoroughly overwhelm you by announcing that not only do you get 11 frame rates, but each of those frame rates can provide three different looks too!  Depending on the time base you select for your program, each of those frame rates can look quite different.  And with three different time bases possible to choose from (24P, 30P, or 60P) that means that each of those frame rates has three different looks it’s capable of.  Here’s the same frame rates, but shot at a 30p time base:

And here’s what the frame rates look like when played back in a 60P time base:

And while we’re pushing things over the edge, let’s point out that due to the way 60P records flagged/duplicate frames, there’s actually FOUR different looks you can attain from each frame rate!  That’s over 40 different looks that can be accomplished, just in 720p mode.

Here’s how it works – each acquisition frame rate is an individually-timed capture of live images.  But how you play those frames back determines what they actually look like, and with three different time bases, you can play them back with three different looks.  So you can’t just assign a certain frame rate with a certain look (for example, you can’t just say “24p = the film look”), because it depends on what frame rate you choose to play it back at.  If you play it back at 24 frames per second, then yes it’s an exact direct mimicry of the film look.  But if you play it back at 60 frames per second, it’ll instead be super-hyper fast motion!

The acquisition rate, and the playback rate, are two different things.  Usually, under normal circumstances, you want them to be the same – i.e., acquire at 24 frames per second, play back at 24 frames per second, and you get real-time action.  Acquire at 30 frames per second and play back at 30 frames per second, and you also get real-time action – a bit smoother than the 24fps/24fps sequence, and less film-like, but still real-time.  Acquire at 60 frames per second and play back at 60 frames per second, and you also get real-time motion.  60fps/60fps looks nothing like film, it looks like “video,” and gives the smoothest strobe-free motion possible.  In the 50Hz version, the equivalent would be to shoot 50fps and play back at 50fps for the “video” look.

But what happens if you acquire at 60 fps and play back at 30fps?  The result is slow motion, a 2-to-1 slowdown factor.  And what if you acquire at 60fps and play back at 24fps?  It’s also slow motion, but it’s even slower: it’s a 2.5-to-1 slowdown factor.  And if you acquire at 30fps and play back at 30fps, it’ll be real-time, but if you acquire at 30fps and play back at 60fps, the result is 2:1 fast motion.  The same frame rate, played back at different time bases, delivers different looks to the viewer.

Selecting your time base, and selecting your acquisition frame rate, are therefore somewhat interconnected when you decide what type of look you’re choosing for your program.  With 24P you’ll have film-like footage, and the most wide-ranging slow-motion capabilities.  With 30P you’ll have hybrid film/video footage – it’ll be smoother/less stroby than 24p, but it will still have some strobing and a somewhat film-ish look to it, and it’ll still be capable of up to 2:1 slow motion.  With 60p you’ll have video-looking footage, with no capability for slow motion but with tremendous fast-motion capability: imagine 1fps acquisition played back at 60fps – it’d be 60-to-1 fast motion.

Because of this, you can’t just think of “60p=slow motion”, because it depends on your playback rate.  60p played back at 60p is the “reality” look, or the “video” look.  The acquisition rate and the playback rate work hand-in-hand to generate the final look of the footage.

Here’s how the same frame rate looks in the different timebases. 

Click on this file to see 12 frames per second shot in the three different timebases:

Click on this file to see what 60 frames per second looks like when shot at all three timebases:

A simple rule of thumb to determine what the footage will look like, therefore, is to divide the playback rate by the acquisition rate.  Acquiring 60p and playing back at 30p, you’d divide 30/60 for a result of 0.5:1.  That means the acquisition footage will play back half as fast as real-time (0.5 times as fast).  That means slow motion.  On the other hand, acquiring at 24p and playing back at 30p would give you a playback rate of 1.25:1, meaning the 24p footage would play back 1.25 times as fast as real-time, for a mild fast-motion effect.  24p acquisition played back at 24fps means film-like footage; 24p acquisition played back at 30fps means mild fast-motion, and 24p played back at 60fps means super-fast motion.

Finally, let’s totally push things over the top by pointing out that there’s a fourth, completely different look that’s possible for each frame rate.  When shooting in the “native” modes (720/24pn or 720/30pn), the camera establishes the acquisition frame rate from the menu and the playback frame rate from the mode you selected (24pn or 30pn).  And the camera only records the chosen amount of frames to the P2 card – i.e., for 12fps, it’ll record 12 frames per second, and for 48fps it’ll record 48 frames per second.  But what happens when you acquire at 60p, but use variable frame rates?

Something very different happens in that case.  When establishing 60p as your time base, the camera always records 60 frames per second, no matter what you establish as the acquisition frame rate.  If you choose 30fps from the “FRAME RATE” menu, and 720/60p as your time base, the camera will image 30 distinct individual frames per second, but will still write 60 frames out to the card.  How does it do this?  By duplicating frames as necessary.  In the case of 30p, the camera will write each frame out once, and then write out a duplicate frame.  On playback, you’ll see 30 distinct and individual frames played each second – but there are actually 60 frames being played back; you just can’t tell because half of them are duplicates so you can’t discern between them.  The result will look visually indistinguishable from 30fps acquisition and 30fps playback.

So what happens when you shoot 24 fps in the 720/60p mode?  Frames are again duplicated, but in such a way as to conform the sequence so that it takes up 60 frames per second.  With 30fps it was easy – just duplicate each frame once, and you automatically get 60 frames.  With 24p it’s a little more complex – each even frame gets duplicated once, and each odd frame gets duplicated twice – so a two-frame group of frame A and frame B (“AB”) gets written to the card as a five-frame group, “AABBB”.  The result, when watching at 60 fps, is that the viewer sees 24 individual frames per second, and it looks very much like film that’s been transferred to video (traditional film-to-video transfers involve the same kind of “2-3 pulldown”).  And when acquiring at 12 fps, each frame will be written to the card 5 times (the original and four duplicates), which means that the viewer will still see 12 distinct frames per second, even though 60 frames are being displayed by the television.

Because the frames are duplicated, the look is very different than what we’ve been heretofore discussing.  We’ve been talking about playing back the frames on a 1-to-1 basis, so 30fps played back at a 60fps rate yields 2:1 fast motion.  But when shooting with the 720/60p time-base, that’s not how it actually works (although you can make it work that way).  Because of the frame duplication issue, shooting 12fps in a 720/60p time-base results in a surreal step-printing look, where it looks like a dream-sequence or almost looks like slow motion.  However, if you conform the footage to get rid of the duplicates, that same 12p sequence played back on the 60p timeline would instead look like super-ultra-fast 5:1 fast motion!

Here’s what the variable frame rates look like in 60p, when using the “step-printing” method of frame duplication:

In the forthcoming The HVX Book and DVD, I’ll be demonstrating how to use the slow shutter speeds and the intervalometer function to add 9 more genuine frame rates, bringing the total up to 20 different frame rates in 720p mode, and using similar techniques we’ll be able to get 7 variable frame rates in 1080 and 480 modes too.  The HVX Book and DVD should be available in February 2006, and will be available for order right here on DVXUser.com.

So there you have it: in 720p, 20 different frame rates to acquire footage at, and four different time-base methods to play it back at (24p, 30p, 60p, or 60p-conformed-to-native).  Nearly 80 different combinations; nearly 80 different creative choices available for you to use.  Combine that with the 7 different frame rates possible in 1080 mode, plus 7 different frame rates possible in DVCPRO50 mode, plus the 7 different frame rates possible in DVCPRO/DV mode, plus you should double the looks possible in DVCPRO50 & DVCPRO25/DV modes to account for both 16:9 and 4:3 shooting modes, and that brings us to a grand total of nearly 115 different “looks” that you can create with the unprecedented, unparalleled AG-HVX200.