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Frame Rate Discrepencies


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#1 Andy O'Neil

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Posted 03 March 2006 - 01:12 AM

Hi,

Shooting on the HVX200
Recording Setup: 720p24PN

Editing on FCP 5.0.4
Sequence Settings:
Frame Size: 960 x 720
Aspect Ratio: DVCPRO HD 720p60 (16:9)
Pixel Aspect Ratio: DVCPRO HD 720p60
Editing Timebase: 23.98
QuickTime Video Settings: Compressor: DVCPRO HD 720p60

Why are there frame rate discrepancies between:
(1) the recording setup of the HVX-200 (24PN) and
(2) the sequence settings: aspect ratio, pixel aspect ratio, and the compressor (60)?

Thanks,
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#2 Andy O'Neil

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Posted 03 March 2006 - 10:08 PM

Maybe I'm lacking a fundamental understanding. I guess I don't know why the Aspect Ratio, Pixel Aspect Ratio, and Compressor are all set at 720p60 (60 being the number in question). I'm assuming the 60 refers to frames per second.

If so, why wouldn't it say 720p23.98 or at least 720p24 since I'm shooting 720p24PN?

Does this make sense?

I'd appreciate any clarification.

Thanks,
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#3 Nathan Milford

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Posted 03 March 2006 - 10:35 PM

The DVCPRO codec always runs at 60fps. The Varicam and the HVX (which uses the same system) will do some mathmatic wizadry and flag specific frames to drop from the 60 to give you anything between 4-60fps. So for any variable frame rate the camera shoots it will lay down the whole 60 frames onto the media to be frame-rate converted when imported into your NLE.

On the HVX, you now have native modes for some frame rates where it will discard the flagged frames before it hits the media, thus 24pn. But the codec is still 60fps

This is a very non-technical description, and I'm not a video engineer... but that's roughly what's going on.
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#4 Matt Irwin

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Posted 04 March 2006 - 11:31 PM

You might want to take a look at Apple's white paper on workflow with the HVX and Final Cut Pro 5.0.4.
Some of it is pretty basic "well, duh" info, but there is some useful info that definitely helped clear up some confusion for me.
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