Rotobrush on long clips

Report · Jul 27, 2019

Hey All. 

I'm using rotobrush on a 17 minute talking head piece to change the background.

 It appears the best work-flow is to trim the long master clip into shorter, manageable segments.

(on my Mac 15 second chunks seem to be manageable)

The rotobrush effect with all it’s parameters is copied with the clip.

But the span remains locked at the starting frame of the first segment so it’s calling for way too much propagation.

I can create a new span by making a new base frame at the in point of the new layer, but because it’s a new calculation based on the pixels in that frame, it won’t match the boundary or the refine brush at the outgoing frame.

Effectively creating a slight jump-cut at each new segment.

Anyone know a better method of doing this??

Thanks

Report · Jul 27, 2019

If the footage was shot with rotobrush in mind, and you can get really good propitiation seventeen minutes will take about a whole day to rotobrush. It could easily take much longer.

You do not want more than a few seconds in any single application of Rotobrush. You also do not want 17 minutes of Rotobrush work in a single comp. The AEP file will be huge and much more likely to be damaged when saving or opening.

The best workflow recommendations that I can give you are:

Only one layer in a comp with Rotobrush applied, 2 maximum, you only want to be creating a matte with this comp
If the layer is longer than just a few seconds as soon as you generate an acceptable matte and freeze the frames drop in a test background layer and check it. If it is OK, RENDER the comp to a visually lossless frame-based production format or at least render just the Alpha Channel so you can use that for a track matte. When the render is complete and the matte has been checked, DELETE the comp or at least the layer.
If you have a long clip break it up into 10 or 20-second segments using the Split Layer shortcut Shift + Ctrl/Cmnd + d, then pre-compose each of the layers trimming the pre-comp to the layer length, do all the roto, render all the pieces, then get rid of all those Rotobrush comps.
Many really tough shots can be color corrected to make Rotobrush easier to use. I've even used Colorama to separate the colors and edges, then pre-composed, then run Rotobrush of the garish pre-comp so I could get propagation to work better. Remember, almost every time, all you are looking for is a track matte.
When using Rotobrush make sure you are only processing frames that are going to end up in the final project. Sometimes you need to add some handles, 10 or 20 extra frames at the head and tail if the final edit is not locked, but generally, every frame that you spend time on that does not end up in the final edit is wasted time and money.

Your seventeen-minute shot could be done in just a few sections but you risk fouled up mattes and wasted time. If all of the shot must have the background removed and there is no way to use some kind of procedural matte, then I would break it up into at least 34 pieces.

I hope this helps. If we could see a few frames of the actual shot we might be able to make some other suggestions that would help you work a little more efficiently. Send 17 minutes to me that was not shot with removing the background in mind and it might cost you a couple of grand to get the work done.

Report · Jul 31, 2019

Hi Rick.

Thanks for taking time to advise.

This is all consistent with my understanding and very helpful.
Thanks You

Report · Mar 26, 2021

Hi Rick,

I've got a similar problem. I'm rotobrushing a 3min video (shorter than 17!), but the propogation rendering appears to only autopropogate for a few seconds then it stops and loops playback. I'm a bit of a newbie, attempting to follow your workflow advice. How do I break the full file up, then work on each individual without it trying to render the whole project as I go?

Thanks, in advance

Rommy

Report · Aug 01, 2021

Did you find the answer? I have the exact same problem

Report · Oct 25, 2021

Same problem over here. one minute clip of a can with blue background gets really slow after 5 sec.