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Timecode phase


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#1 Phil Rhodes

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Posted 09 February 2008 - 06:45 AM

Hi,

I have an interesting challenge with an electronics problem I'm working on.

Assume I have a VTR or disk recorder recording picture and I'm taking timecode from a lockit box or other sound-centric timecode source. Both are running at the same frame rate, but they are not phase locked together. Tiny amounts of drift between the frame rate of the video source and the lockit will occur. If I mark each video frame with the last timecode reported at the beginning of that frame, I will eventually end up marking two frames with the same timecode, or missing one timecode frame out entirely, as the differential phase drifts through the point at which I'm reading the information.

This may be poorly explained, but this must be an issue for every piece of sound or picture recording gear ever made and there will presumably be a standard approach to it.

Having thought about it, the solution that suggests itself is to read the timecode at the start of recording, and increment internally on every recorded frame thereafter. I can't see a problem with doing it that way, but I'd prefer to be doing it the same way as everyone else. Any information gratefully received.

P
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#2 John Brawley

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Posted 09 February 2008 - 08:00 AM

Hi,

I have an interesting challenge with an electronics problem I'm working on.

Assume I have a VTR or disk recorder recording picture and I'm taking timecode from a lockit box or other sound-centric timecode source. Both are running at the same frame rate, but they are not phase locked together. Tiny amounts of drift between the frame rate of the video source and the lockit will occur. If I mark each video frame with the last timecode reported at the beginning of that frame, I will eventually end up marking two frames with the same timecode, or missing one timecode frame out entirely, as the differential phase drifts through the point at which I'm reading the information.

This may be poorly explained, but this must be an issue for every piece of sound or picture recording gear ever made and there will presumably be a standard approach to it.

Having thought about it, the solution that suggests itself is to read the timecode at the start of recording, and increment internally on every recorded frame thereafter. I can't see a problem with doing it that way, but I'd prefer to be doing it the same way as everyone else. Any information gratefully received.

P



Hi Phil.

Not sure if you've thought of it or are aware, but you can get gen-locakable jam syc clocks. Not sure about Lockit but the Aaton GMT's are certainly phase locked and can have a GEN lock.

Aatoncode-2 also *gen locks* film cameras too....

jb
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#3 Phil Rhodes

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Posted 09 February 2008 - 11:54 AM

I was aware of that, but it's a case of needing to ensure that it'll work with whatever I'm thrown.

The only solution I can think of is what I mentioned - to grab the timecode which was most relevant at the first frame and go from there - so that's what I assume people do. I'm just not dumb enough to assume I've thought of everything :)

At the end of the day, that's all you're doing when you wave a timecode slate in front of a film camera.

P
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