Rotobrush on long clips

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:

1. Only one layer in a comp with Rotobrush applied, 2 maximum, you only want to be creating a matte with this comp
2. 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.
3. 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.
4. 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.
5. 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.