Why does masking slow render time so much?

[kylet58430735]

So the first comp I made had this problem, though I didn't realize it then. I had a comp I was making and i didn't want parts of it to show up so I added a black solid and multiplied it with the video, whitening the areas I wanted to show. The resulting comp took almost 3 days to render. The next comp I made I didn't need to do this and it rendered at an exponentially faster rate, only 3 hours, even thought it was longer and had more effects. Today I went to render, using a mask again, and left for work. When I came back the estimated time had risen to 44 hours and it was maybe rendering a frame every 2-3 minutes. I thought maybe the effects were slowing it down so I deleted all of them, planning to use another program to added them. I restarted and still had the massive lag in render time. Then I got the idea to delete the mask and boom, it's racing through the frames and finished in 4 hours.

Why does adding a mask slow things down so much and is there a way I can stop this from happening?

[Mylenium · Accepted solution]

Per se masks do not influence render time more than effects. Simply sounds like you have set your comps to Raytrace 3D instead of Standard 3D and the masks are being evaluated as contours for generating geometry. Though, to be honest, based on such non-information it's impossible to make sense of your longwinded write-up. You simply haven't provided any useful information like version of AE, system info, details about your comp, where the mask is applied, render settings and so on. You need to do better and give us something we can actually work with in order to unriddle this problem.

Mylenium

[Andrew Yoole]

I agree with Mylenium that those kind of crazy render times suggest you might be working in Raytrace 3D mode.  Go to Composition Settings/3D Renderer to confirm you are using the Classic 3D render engine.

If that doesn't work, feel free to post a link to a copy of a problem project and we can assess what's going on.