Black bar appearing when wipe on masked layer
As you can see from the video, when my OSG layer wipes on, a black bar the same shape but at 100% scale appears in the middle, wiping off symetrically.
This black shape doesn't appear in the preview when paused, but if playing or scrubbing it appears and, crucially, it appears in the render.
To create my OSG, I have 1080x1920 sequences, with the text in, and then when I place this into the scene, I create a mask to crop the background to around the text.
Can anyone help me get rid of this please?
Thanks!