Magic Mask not working on a split clip

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z.bielicki88

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Magic Mask not working on a split clip

PostFri Oct 11, 2024 12:19 am

1. I have a timeline with one long clip on it
2. I apply magic mask to the whole timeline via the color page, to separate a single actor from a green screen background.
3. Using the magic mask overlay, I tune and improve the mask by making multiple keyframes and tracking it all out
4. I split the clip via edit page
5. The masking for any part of the clip to the right of the split is gone, and though I can retrace it in the color page, the tracking buttons no longer work. I can, however, retrack and edit the mask on the clip to the left of the split. This continues to happen if I make more splits to the left clip, with the clip to the right of the split.

Why is this?
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KrunoSmithy

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Re: Magic Mask not working on a split clip

PostFri Oct 11, 2024 7:54 am

This is a reoccurring theme it seems, that users post about and probably Blackmagic should be better at explaining how it all works.

Magic Mask in particular, is sensitive to how you tread it upstream vs downstream in the workflow. Much like fusion nodes or color page nodes, there is a flow to consider. And magic mask is a color page effect so it behaves like that.

The basic rule is that you can do almost anything downstream and almost nothing upstream or you will break the tracking information and have to retrack, because magic mask gets its information to track from edit page. Or nodes before in the color page. I'm not counting fusion here because that is extra layer to consider. However if you have made your tracking on edit page timeline, than you are only seeing a preview of magic mask on the timeline in the edit page. The real information is in color page. Because it happens downstream of edit page.

So when you make tracking with magic mask on color page, you are feeding something from edit page to it to track. once it has tracked it, it will remember reference frames and strokes independently of anything else, but to track the rest of the footage it needs information from edit page. If you change source of what is used for magic mask to track, it will have to be retracked, with exception of the reference frames remaining intact, because they are not cached.

Regarding split clips, if you apply magic mask to original clip on your timeline, and than you chop it up into parts, you will only preserve tracking on the original part which was tracked, with the rest you broke the connection because you have made a change upstream of what magic mask is using as source for tracking.

As I've said, upstream from Magic Mask will break everything, downstream will break virtually nothing. I think that in your case there are far better ways to work with green screen footage, but if for some reason you want to make it more complicated and still have a split clip with magic mask there is a little known way, that is logical if you follow the concepts I mentioned. Upstream vs downstream.

Create a compound clip of your video clip on the timeline. Right click on the compound clip and choose open in timeline. Than new timeline in the tab called compound clip should appear. In that timeline, that you just opened, apply magic mask. And it will be applied to your compound clip on original timeline. Now you have protected the clip from breaking the connection at the expense of working with compound clip. But now you can chop it off anywhere you like or duplicate it and it will retain magic mask track. You would have to make changes to magic mask if you like in the compound clip timeline itself. But compound clip on original timeline is now prevented from breaking the connection, in a direct way.

Another way is to use fusion which sources from media pool not timeline hence it won't break the connection either, but if you do green screen, fusion is probably best place to do it all. Not edit page. Edit page is for editing not green screen work. And its something that is in the pages or modules of resolve, before fusion and color page. That is a hint of what should come first and in what order. While some overlap exists and there are ways to work between the pages, its not a best thing, its usually what people do when they don't understand how it all works and try to stay where they are most comfortable, which is usually edit page. But it leads to more problems than it solves because it goes against the way resolve is designed and intended to be used.
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Andy Mees

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Re: Magic Mask not working on a split clip

PostFri Oct 11, 2024 8:07 am

z.bielicki88 wrote:Why is this?
By splitting the clip you've orphaned the right hand side MM instance from its reference frame (which is in the left hand side clip) ... you can't re-track it because it has no reference frame to track from.
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Jim Simon

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Re: Magic Mask not working on a split clip

PostFri Oct 11, 2024 2:42 pm

z.bielicki88 wrote:2. I apply magic mask to the whole timeline via the color page, to separate a single actor from a green screen background.
That's not really what the Magic Mask is for. You should try the proper tools in Fusion for this.
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Marc Wielage

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Re: Magic Mask not working on a split clip

PostSat Oct 12, 2024 10:46 pm

z.bielicki88 wrote:4. I split the clip via edit page... 5. The masking for any part of the clip to the right of the split is gone, and though I can retrace it in the color page, the tracking buttons no longer work. I can, however, retrack and edit the mask on the clip to the left of the split. This continues to happen if I make more splits to the left clip, with the clip to the right of the split.

Before you split the clip, render it in place to a high-quality codec like ProRes 444 or DNxHR 444 in the same resolution as the original clip. Do that and then split the clip, and this won't happen.
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