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External mattes are out of sync: suggestions?

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Michael McCune
External mattes are out of sync: suggestions?
on Mar 8, 2017 at 7:57:46 am

... There is always a reason, but not obvious. ... (In)famous philosopher, me.

The goal is to use a clip exported from Resolve, use Fusion to create a matte (which it does very well), then, back in Resolve via an external matte, correct for color, etc.

This works almost.

In short, the matte is imported and works except that it is offset in time, verified with burned in time code.

Very simple base case:
Using tiff throughout to reduce codec uncertainties; no handles to eliminate that as a potential error source; simple one minute clip.
Export the clip from Resolve as tiff.
The clip is then imported into Fusion and a matte is created in Fusion for the face. Works. Time code is added to the Fusion node tree for export, mainly to confirm the start and end points.

FWIW, I am reminded that Simon Ubsdell seems to have mastered keying and has wonderfully precise and clear tutorials, and one of my favorites is his "procedural garbage matte" technique in Advanced Keying Techniques --



-- is a lesson worth approaching and it is from someone so very highly skilled.

Anyway, back in Resolve, import the Fusion clip as a standard video clip, not as a matte. Then drop it on a new track over the original source track. Note that this Fusion clip when imported as video lines up perfectly, frame for frame, and that the burned in time code on the Fusion clip has the same correct start and end frame numbers. So we know that the Fusion clip is working as expected. At least as video.

Now re-import this same clip into Resolve as a matte (may first have to delete that Fusion clip imported as video from the working bin). Note that there is no offset option when importing as a matte.

In the Resolve color page add a node for the purpose of hanging an external matte from it. Note that we should have a simple image of a face and time code is displayed.

Next, with the external matte node set up and now displaying the matte in the video node, make a radical adjustment in, say, brightness, just to highlight the mask in an obvious way.

Now note that the Fusion matte is slightly offset from the Resolve video image. Note that the video time code is displayed and that the Fusion matte also has its time code showing.

They don't match. The two time code readouts are usually off by about 37 frames. That is, instead of a start frame number of zero the matte shows a time code of 01:00:01;07. Consequently the matte is also visually offset from the Resolve video image.

As they say in the 'hood, "What's up with that?"

Again, recall that this same imported clip lined up perfectly when imported as video and placed in the timeline above the original source track.
BUT, imported as a matte this same clip is consistently off by a certain number of frames.

So it seems that the Fusion clip was created correctly for this purpose but it slides into Resolve as an external matte with an offset.

And there does not seem to be any method of offsetting the matte clip once it is imported.

Any thoughts??? I would be glad to play the dummy (been there, actually, sooo many times). Could someone point out something simple and obvious???

Thanks guys (and girls, if there are any out there), Mike


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Tero Ahlfors
Re: External mattes are out of sync: suggestions?
on Mar 8, 2017 at 8:54:23 am

Do they run at the same frame rate and are they the same length? I've never had any issues with just bringing external mattes in. Have you read the manual?


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Michael McCune
Re: External mattes are out of sync: suggestions?
on Mar 8, 2017 at 7:08:23 pm

Tero; thanks for the reply.

Perhaps I was not clear about the fact that the same Fusion clip is imported into Resolve both as a video clip and as a matte.

In the case of the clip imported as video and placed on a track above the original source track, the time code matches at head and tails, so perfectly in sync.

But in the case of the import as an external matte however the time codes--and the visual matte--do not match and are visually out of sync.

So where would the issue of a frame rate difference enter into the process???

Thanks, Mike


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Glenn Sakatch
Re: External mattes are out of sync: suggestions?
on Mar 9, 2017 at 3:00:53 pm

what frame rates are you working in. I'm guessing 29.97, as you said it was a 1:07 offset which equals 37 frames...but is that the frame rate you worked in in fusion as well? Is I possible the matte you created is 23.98 and resolve is bring it back in at a different frame rate?

(you sure do have a lot of issues with mattes :))

Glenn


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Michael McCune
Re: External mattes are out of sync: suggestions?
on Mar 10, 2017 at 1:37:59 am

Glenn; I was hoping you would chime in. Yes, trouble with mattes.

And, yes, all the work, from source to final, is 29.976.

You asked about my Fusion frame rate setting. So let's start with my confusion over setting the Fusion frame rate:

Just for fun, try a search for, "29.976" in the Fusion User Manual or the Fusion Tool Manual (try Ctl+F to bring up a local search box for the document). What do you find??? There are NO entries in either manual for the term, "29.97" or for, "29.976."

First, we note that Fusion has two "frame format" setting locations within Preferences, under Global and Default Settings and under and Composition/General.

These frame format pages each have frame rate data entry fields but they are pre-populated only with whole number integer frame rates, such as, "24, 25, 26, 27, 28, 29, 30, 31," etc. Again, no "29.976 option.

But it seems that it is possible manually to enter a fractional frame rate in these fields. But not really.

That is, the frame rate field entry is constrained to two decimal digits, e.g., "29.97." We know the actual frame rate is, '29.976." So it is not possible, either by choosing an item in the drop-down list or by entering, "29.976" in this field.

So how is one supposed to understand this frame rate setting business in Fusion???? Seriously, what is the logic???

FWIW, the frame rate--so says the documentation--is determined by the frame format which is resolution independent. Don't quite follow the logic, however.

Or, try a search for, "frame rate:" there is ONE entry in the Tool Reference but it only relates to stretching duration. In the User Manual it says, "Since Fusion is
resolution independent, comps do not ask you to define a resolution or frame rate. Those settings are determined in the Globals [sic] Frame Format preferences," (from page 25). Don't understand how resolution--to me that means the total number of pixels, horizontal x vertical, in some HxV ratio that is the format-- can yield a rate. That is, a given format, say, 1920x1080, can be recorded at widely variable frame rates.

So how to they get there, a derived frame rate???

(Somewhere in this mix is also the question that the tiff file format does not have, I understand, ANY integral information about frame rate, as might be embedded in other codecs and file formats.)

If you find you have any helpful corrections or thoughts on this, Glenn, glad to hear them!

Thanks, Mike


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Glenn Sakatch
Re: External mattes are out of sync: suggestions?
on Mar 10, 2017 at 2:19:13 am

Just to clarify, 23.98 is actually 23.976. I've never heard of 29.97 referred to as anything other than 29.97...(maybe as 30), but i wouldn't enter the number as 29.976...I doubt if that would cause the problem you are describing, but i would start there.

Try entering that in fusion. If i get some time i'll try a couple of tests tomorrow. To be honest, i very rarely work in 29.97 anymore, so i'm not sure if i've ever output it from fusion, but i have definately done what you are trying in 23.976 with success.

Glenn


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Michael McCune
Re: External mattes are out of sync: suggestions?
on Mar 10, 2017 at 8:08:09 am

Thanks, Glenn; you are right I believe about the number: 29.97 vs. 29.976.

BUT THE SOLUTION TO THE MYSTERY OF THE EXTERNAL MATTE FRAME OFFSET IS AT THE END OF THIS POST!

There are many online references to 29.976 but there is no derivation for that which I could find in a brief search today. So I agree and lets stick with 29.97.

As you must know, the 29.97 number comes from 30/1.001, which harks back to the first color TV days and their need to shift the frequency harmonics slightly. I understand that to reduce all the phasing from the color subcarrier, etc., they had to calculate out several orders of harmonics. Amazing. And they did all the math without computers.

Anyway, here is the actual solution, to the external matte offset problem, gleaned from this tutorial,



, which mentions that imported external mattes line up with the start of the original clip, presumably the source time code.

And, indeed, my test clip had been shortened at the head by about 37 frames.

So, if one exports a portion of a clip starting at some point into the clip, not the start of the clip, and then the Fusion matte made from that portion is imported back into Resolve as an external matte it will not line up, as expected, with the start of the exported portion of the entire clip. Rather the external matte will line up with the start of the entire clip prior to export.

Why??? Dunno. Something that could be clarified in a later version of Resolve, sez I.

But how to fix it??? ANSWER: The external matte key tab includes an offset option. This critter is difficult to manage due to very high sensitivity: slight mouse movements can translate to relatively huge frame increments or decrements. And there is no nudge keyboard option that I know of.

With some fiddling with this control, the -37 frames adjustment did offset the matte to match the original video.

Funny but I tried this option before but gave up, supposing I didn't understand how to use it as it would jump wildly in the frame count even with tiny mouse movements. And of course I needed only about 37 frames. (Actually, I wonder if the huge offset range results from scaling the long length of the entire original clip: not hard to jump to an offset with hundreds of thousands of frames. But this behavior makes small changes of a few frames tricky and actually difficult.

So I guess Resolve might include this as a feature request and refine this option to provide some sort of scaling and nudge capability.

Thanks again, for the commiseration, Glenn. Mike


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