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Over/Undercrank

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randy Strome
Over/Undercrank
on Jan 14, 2008 at 1:43:35 pm

Philip on his blog mentioned that he had shot the slow motion in his short, "Most of it was shot at 720p 25 60fps". That made me realize that I am missing something about overcranking. What is the difference between 720p 25 60fps and 720p 60? Is there one?


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Craig Seeman
Re: Over/Undercrank
on Jan 14, 2008 at 3:05:16 pm

I've shot 720p24 overcrank to 60p. In that overcrank mode there's no audio. Edit in your NLE in 24p time base and the p60 shots drop in the timeline already slowed down.

Theoretically the data rate is much higher during overcrank 60p record so playback at the 24p timebase is at the 35mbps VBR data rate. As an aside, this is probably one of the reasons that may differentiate SxS cards and other data file cards. In overcrank mode the record data rate may have to be sustained at around 100mbps VBR and then some headroom on top of that.

In "normal" 720p60 audio is recorded. If you drop it into a 60p timeline it plays at "normal" speed. What you get for this p60 over p24 is much greater temporal resolution. The record data rate is 35mbps VBR. So if you slow this down to 24p you're getting less data per frame.

So your options are:
Shoot 720p24 and overcrank to 60 for slo mo shots (no audio)
Shoot 720p60 with audio and work in 720p60 timeline (no slow mo)
Shoot 720p60 "normal" with audio and drop that in 720p24 and you have slow mo with slow audio and probably lower data rate per frame.



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randy Strome
Re: Over/Undercrank
on Jan 16, 2008 at 12:38:59 am

[Craig Seeman] "I've shot 720p24 overcrank to 60p. In that overcrank mode there's no audio. Edit in your NLE in 24p time base and the p60 shots drop in the timeline already slowed down."

Please tell what role the 24 plays in a 720p24 overcrank to 60p scenario. Can one set for instance 720p30 overcrank to 60p?

Thanks again.

Randy




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Craig Seeman
Re: Over/Undercrank
on Jan 16, 2008 at 1:27:20 am

You'll get the greatest slow down in 24p but you can certainly do a 30p time base and PAL area folks are doing 60p in a 25p time base.

Actually one can do 1080p24 and do a very slight overcrank to 30p too.



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randy Strome
Re: Over/Undercrank
on Jan 16, 2008 at 2:56:15 pm

Thanks for your patience,

I am still missing something. My understanding is that under/overcranking allows for any recorded frame rate in one frame increments from 1 fps to 60 fps. I now, thanks to this forum, understand that overcranked 60P is without audio and ++ data rate as opposed to regular 60P.

But waht I do not understand is the function of the base frame rate i.e. 720P 30 overcranked to 60 or 720P 24 overcranked to 60. Drop the two clips into a 30fps timeline and the playback speed should be identical (1/2 of the original), no? Is there another difference?

Thanks again,
Randy





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Craig Seeman
Re: Over/Undercrank
on Jan 16, 2008 at 3:13:55 pm

Drop an overcrank p60 clip in p30 timeline and it plays at half speed.
Drop an overcrank p60 in a p24 timeline and it plays at 40% speed.

Timeline should match the BASE speed p24 or p30.
You shoot EITHER p24 Overcrank 60
or
p30 Overcrank 60
or
p25 Overcrank 60 (for PAL area folks)
You set your base at the beginning of the shoot/project. You use the Slow/Quick motion to set Overcrank when you use it. It's always in the Time Base you previously set up.

I don't get what you're missing. It's really SIMPLE.
Your time base (you choose when you set up to shoot). Then you set up overcrank record when you want to.

Your Project/timeline in your NLE must MATCH your timebase or you'll be doing rendering.



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randy Strome
Re: Over/Undercrank
on Jan 16, 2008 at 3:36:48 pm

Thanks again,

There is no simple for me :)

In, for instance, an all slow motion shoot, where nothing will be shot at the base rate (say 24 P), the overcranked 60fps is really the only frame rate. It sounds like 24P in that instance is more of a handling note to the NLE.



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Craig Seeman
Re: Over/Undercrank
on Jan 16, 2008 at 4:51:04 pm

You must shoot in a time base of either 720p24, p30. p25. What you actually do with the video after that is up to you but "slow" is relative to "something" and the somethings are the above timebase choices.



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randy Strome
Re: Over/Undercrank
on Jan 16, 2008 at 4:58:46 pm

[Craig Seeman] ""slow" is relative to "something" and the somethings are the above timebase choices."


Are they? Or are they relative only to the timeline playback speed they are dropped into?




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Craig Seeman
Re: Over/Undercrank
on Jan 16, 2008 at 5:17:10 pm

Those are timeline playback settings too. One can always set up custom timeline settings and one can always render but timelines are generally 23.98 (or 24), 25, 30, 60 in the world as I know it.



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