A few questions on VFR

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Phil1076

Well-known member
Ok, I understand VFR but, having never owned a VFR-capable camera, I'm trying to grasp a few concepts...

What, exactly, is the point of VFR if fast/slow motion can be done in post easily?

If I want slow mo, I'll record a scene at 60p and drop it into a 24p timeline.

What is the benefit of overcranking? How does it work? How does the camera record 60 frames when it's set to 24p?

And undercranking....say I set it to record 2fps...does it actually record 2 frames in on second? Does it use less space? Why not just record standard 24fps and then speed it up in post?


Thanks
 
When you look at a camera, I like to think of it as a multipurpose tool. Some toolboxes have rachets, some have screwdrivers, some have both. Some cameras have built in ND filters, some have full frame sensors, some have focus assisting and some have audio embedded.

VFR, aka overcranking and undercranking, is just another tool in the box that allows you to use a technical asset to make a creative or stylistic choice. For example http://www.youtube.com/watch?v=pKd06s1LNik was shot at 36fps, but the sync was make so that their mouth movements would be in sync with the final music playback. The result is something that feels as dreamy and buttery as the song's sound.

It works by playing the framerate selected in your specified timebase. If you shoot at 2fps, it will take 12 seconds to record 1 second of footage. It functions similar in the way and intervalometer works on a still camera. The recording data rate will be lower, but the final playback will be the same data rate. You can record longer on a single card, but the final card will have the same duration of footage on it.

Speeding up or slowing down footage in post is typically accomplished two ways: by blending frames or by stretching out the duration of a single frame over a longer span of time. The final result is almost never as smooth as doing it in camera. And, it requires time and processing power. There are plug ins that can assist in accomplishing the same means, like twixtor, but again, it takes time to do it in post. Time=money. Less time saves costs. And, i don't think it can be done nearly as easily in post as it can in camera.

When you know that it's the look you want, why not just get it the way it's meant to be, and the way it's been shot for decades.
 
One incentive with the AF100: VFR allows you to shoot 1080p50/60. It also allows for those increments between the usual 24, 25, 30, 50, and 60, most of which have some use.
 
Hi Phil

The way I got my head around the variable frame rates was to think of the final output frame rate (For example 24 fps) as a bucket. Then you variable frame rate (60 fps) is what you put in that bucket.

Post software doesn't have this information stored in the frames or "buckets" . So out of the 24 frames that it does have it has to make up those other frames. There's some clever ways it goes about doing this, but none are as good as having those original frames in the first place.

Hope that made sense?


Pete B
 
Phil1076 said:
Ok, I understand VFR but, having never owned a VFR-capable camera, I'm trying to grasp a few concepts...

What, exactly, is the point of VFR if fast/slow motion can be done in post easily?
Click to expand...

Because shooting whole frames natively is better than interpolating frames to a new frame rate. You also have many more speeds available to you to do it.

If I want slow mo, I'll record a scene at 60p and drop it into a 24p timeline.
Click to expand...

That's fine, but it's work you actually have to do yourself, and you rely on the quality of your NLE's ability to do the interpolation. Doing it with a single step in-camera gets it done as you shoot and ensures each frame is a whole, native frame, not an interpolation. All you have to do is put it on the timeline, nothing else.

And, you have many more options than just 60 to 24, many more grades of slower or faster motion.


What is the benefit of overcranking?
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Any time you shoot a faster frame intending to slow it down for playback, that's overcranking. It's what you do when you shoot 60 and slow it down to 24.

How does it work? How does the camera record 60 frames when it's set to 24p?
Click to expand...

It's pretty much the same as you shooting still pictures in groups of 60, but laying them out in order in groups of 24.


And undercranking....say I set it to record 2fps...does it actually record 2 frames in on second?
Click to expand...

Yes.

Does it use less space?
Click to expand...

For the amount of time you've shot, yes.

Why not just record standard 24fps and then speed it up in post?
Click to expand...

For the same reasons stated above.
 
If you haven't got it yet from the above replies....the bottom line is: It just works better, it just looks better.
 
1080 60 from the AF100 plays back 40% speed in a 24 timeline. Some say it is putting up to 35mb/sec of data on the card. All of the slower shots in this clip are from the AF100 in 1080 60 in a 24 timeline. There are a couple 1080 24p shots from the GH2. AF100 lens is the Voit .95 and GH2 lens is the Lumix 14-140.

http://vimeo.com/28090105
 
I have just shot some VFR footage at 50fps. It looks 50fps in camera but when I play the file in VLC it seems to think its 25fps and its slowed down. Same with Premiere Pro. It think the source file is 25fps.

Why is this?
 
Well, you shot VFR -- that's exactly what it's supposed to do. VFR only works when you have the camera in 1080/25p mode. So when you set a frame rate of 50fps, it images 50fps and records them, but the file is set to play back at 25fps, and therefore you get film-style frame-accurate slow motion.
 
Barry_Green said:
Well, you shot VFR -- that's exactly what it's supposed to do. VFR only works when you have the camera in 1080/25p mode. So when you set a frame rate of 50fps, it images 50fps and records them, but the file is set to play back at 25fps, and therefore you get film-style frame-accurate slow motion.
Click to expand...

Ah makes sense. Just shot some amazing slo-mo today. The Af100 is fantastic!
 
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