Roto Brush Masking Not in Correct Place On Exported Video

[David2498646303lk]

Hello, I have rotobrushed my subject over an image. As you can see, in AE the preview looks fine...

and the roto mask is tidy around the torso...

But when I export... the mask is about 10 or 15 pixels forward of where it shoud be...

In AE:   Exported: 

I have the base layer video, the 3D camera tracker, my logo text as a PNG, and then a copy of the video on the top with the Roto Brush applied.

The top roto'd layer doesn't have any transforms on it, it's a straight copy with the roto.

Does anyone have any ideas what I can look at to resolve this please? Many thanks.

[David2498646303lk]

To clarify, by "mask" I mean the one created by the Roto Brush. I have done no manual masking.

Also, I have frozen the Roto in the layer once I was happy with it. 

[David2498646303lk]

I have started again from scratch to make sure I hadn't messed anything up and it's doing the same. One thing I noticed now, having not roto'd out the whole person, is that the video is actually lagging behind the roto brush, as you can see below, where the roto'd part is lagging behind her leg...

Not sure if that gives anyone any clues? Thanks.

[David2498646303lk]

So I figured it out. It was something to do with the frame rate. The footage was filmed on a film using Open Camera. It recorded in 30.0042 frames per second. 

I think the roto video portion was one frame behind for some reason.

To fix it, I created a new Premiere Sequence at normal 29.97 fps, imported the footage (which asked if I wanted to change the sequence settings, I said no), then exported it at normal 29.97 fps.

Top tips for you there!