After Effects slows down when rendering/playing clip, what am I doing wrong?!

[lowlight27]

Trying to add some effects to a video at work and it keeps slowing down and pausing. What am I doing wrong? Is there a simple setting that I'm missing? I'm new to after effects and hope to really use it for our upcoming videos. Please can someone help me? I attached a video of what i'm trying to fix.

[Rick Gerard · Accepted solution]

That's just a normal preview running out of RAM. If you have not got a green line all the way across your timeline and you can't get one when you run a preview then your system does not have enough RAM to render a preview of the entire timeline.

You can get better performance and longer real time playback if you set comp resolution to half. I usually set my comp resolution to Auto and work with the Magnification Factor at 50% for previews. When you get more experience with AE you will be spending much less time running previews and you will only use 100% magnification factor and full resolution to check a few frames for critical positioning and edges then move on to the rest of the project. AE is not a video editor. It is designed to produce shots that you cannot create any other way. Most of my comps are seven seconds or less and more than 95% of all my editing is done in Premiere, even if every shot requires an effect I can only create in After Effects.

If you have a bunch of videos to do and you need to separate your actor from the background it would be a good idea to invest in a folding green screen or just go to the fabric store and buy some green no-iron fabric and use that for the background. Then simple stuff like this can be done in Premiere Pro using the standard keying effects in a couple of minutes.

If you had to use Rotobrush to separate an actor from the background you are stuck with After Effects. If that is the case the most efficient workflow is to do the rotoscoping, check the edges carefully using a temporary background, and then render a Digital Intermediate using a visually lossless format with an alpha channel. The rendered footage could then be used in After Effects or Premiere pro to complete the composite. There's no real reason to use After Effects for simple background replacement unless you are trying to simulate light wrap, match camera movement, or do the kind of color corrections that are required to make you believe that the shot is real.

I hope this helps.