Help understaning the Variable Frame Rate mode

Darkline

Darkline

Veteran
Hi All,

I know this has been covered a few times, but there are certain things I dont quite understand about how this mode operates...

Firstly, I am told that in variable frame rate mode the camera can record from 12fps up to 60fps (maybe more) . However I'm told the PAL model can only shoot up to 50fps as thats part of it's design/codec limitations.

the 25/50 (PAL) restriction seems to be intrinsically linked to the codec and electronics within the camera. However if the USA model of the camera can support 10 or more different framerates up to 60p, then surely this also would be limited by the 60i limitation. In other words, surely the PAL model could do all those framerates too?

My educated guess is that the camera is not limited to a certain frequency of shooting, but rather one of the encoded stream which is limited. Therefore you can shoot at any of these framerates but the encoded stream will be saved as a 60i stream (or on PAL 50i stream). Is that correct?

I guess there are two ways to do the vari-modes..... one to 'flag' the active frames within the stream as 24p works, and another would be to pre-encode the framerate into the 60i/50i stream....

let me explain what i mean by 'pre-encode'. If I decided to shoot 60p (on the PAL camera) then theoretically it could say ...'well this is going into a 25p project, so this 4 second 60p shot will actually be recorded as a slo-mo 9.6 second 25p shot'.. This way you could film 60p on the PAL model and have no problems with codec limitations. It would till be a PAL stream and import as pre-slomo'd into your editor.

However I think I've been told that PAL will not do 60p, so this leads me to think it flags active frames within the 50p stream, so unfortunately it canot go greater than 50p as thats the most the codec stores. So here I understand that 60 doesnt go into 50....doh!

So, Im hoping it does it the other way, and having looked at the new brochure for the PAL HVX, it does mention shooting slo-mo at 60p (tho it isnt in the specs at the end). So it leaves me wondering. Are any of the framerates for PAL confirmed?

Secondly, how does the camera know what you're final editing framterate will be? Do you first select the destination framerate (30p/ 24p/60i), and then choose a variable framerate within this? In other words is the variable frame rate a sub-set of 24p/30p/60i modes individually? Or is this done on import to the editor? If I shot a 60p vari-frame clip, does this mean I could bring that into a 24p/30p or 60p project?

Hope this hasnt been too confusing, and thanks for your help in advance.
 
Darkline said:
(...)

the 25/50 (PAL) restriction seems to be intrinsically linked to the codec and electronics within the camera. However if the USA model of the camera can support 10 or more different framerates up to 60p, then surely this also would be limited by the 60i limitation. In other words, surely the PAL model could do all those framerates too?

My educated guess is that the camera is not limited to a certain frequency of shooting, but rather one of the encoded stream which is limited. Therefore you can shoot at any of these framerates but the encoded stream will be saved as a 60i stream (or on PAL 50i stream). Is that correct?

(...)

Secondly, how does the camera know what you're final editing framterate will be? Do you first select the destination framerate (30p/ 24p/60i), and then choose a variable framerate within this? In other words is the variable frame rate a sub-set of 24p/30p/60i modes individually? Or is this done on import to the editor? If I shot a 60p vari-frame clip, does this mean I could bring that into a 24p/30p or 60p project?

Hope this hasnt been too confusing, and thanks for your help in advance.
Click to expand...
Good questions!
 
You're asking questions that I don't think any of us know the answer to yet.

I am 85% certain that the European model will offer a maximum frame rate of 50fps; I don't think the codec handles more than that. But, until the European model announces its specifications, we won't know.

They've said that the variable frame rate effect can be seen in-camera on playback, so that would imply that your guess is probably on target -- that it's actually recorded as a 25p stream, even though there were 50p frames shot. I think that's what the Apple Cinema Tools program can do too, right? Can't you tell it to treat a 30p clip as if it had a 24p timebase, so it plays back at slower motion? Anyway, that sounds reasonable as to expect how the HVX would work. But then again, you have to be able to shoot 50p as 50p also, for "reality"-looking video, so... hmmm...
 
Thanks for the reply Barry.

That's what I was thinking, and 'IF' the vari-frame is indeed a 25p stream then in theory there is no reason why you couldn't shoot at 60p on the PAL model; all it would do would be to save a longer 25p stream clip. It gets around the codec limitations.

thanks for the input; I didn't know whether this was established info or not yet; I guess not so we'll wait and see...
 
Darkline said:
then in theory there is no reason why you couldn't shoot at 60p on the PAL model
Click to expand...
Not true. The Euro DVCPRO-HD codec is different than the US version. It uses a different-sized pixel grid in 1080, and different compression per frame in both modes. You can't fit sixty frames of Euro DVCPRO-HD into 100 megabits, it would take a completely different codec to do that.
 
I'm not talking about fitting 60 frames into the DVCPRO-HD codec. Im talking about taking the 60 frames that have been shot and re-sequencing them into a longer 25p stream. What you end up with is not a 4 second shot at 60p, but a 9.6 second shot at 25p. This gets around the codec limitations. I was hoping this is how it would work.

You already said that you can shoot onto the P2 card and then record that slo-mo over to DV25. So this is doing the same thing - resequencing a vari-shot into a longer slo-mo 25p strewam. The result is always a 25p stream no matter what the framerate used. There is no need to fit 60 frames into the codec.

Lets say you shoot 1 second of 60p. I know the cocdec could not store that 60 frames in 1 second, but it could store a 25p 2.4 second shot. Using this method there is no reason why you could not take advantage of the 60p slo-mo feature.
 
Except that the crystal in the camera runs at 50hz, not 60. 60 is only available on the US version because the timebase it uses is 60hz (well, 59.94hz actually). Doesn't exist on the European version because it's based on a 50hz timebase.
 
ok that makes sense but its right on the edge of my techincal understanding...lol

I get that the cams are linked by the frequency of the gubbings. I assume this has to do with US mains electricity being 60hz and UK elctricity 50hz. I guess thats where the differences started originally. Really odd tho since they are all step down'd to a DC voltage anyway.

So lets say you had a camera that could shoot 500fps (which some do) are you saying the crystal also needs to operate at 500hz? I guess that adds up
 
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