Today i started to render a video clip which have at least 20 videos with green screen keygen and a lot of effects like smoke, color correction etc. The video is 3 minutes and to render it i need 6 hours... Is this normal, i have to change some settings or i need to upgrade my computer? My computer is Intel Core i3, Graphic Card: GT440, 8GB Ram.
Are you working in HD? Seems like if there's lots of effects, keying smoke and color correction that it could easily take 6 hours. We need more information to give more detailed feedback though.
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We need a lot more information about your project to make any reasonable assessment of the time required. I've had keying projects that would render at one frame a second, and keying projects that took 10 to 15 minutes per frame. It just depends on what you're trying to do.
Yeah I've had projects where sections have taken that long per frame especially if there's tons of lights and 3D layers. If you're running AE CS5 there's a useful script for background rendering that gives you the time taken per frame so you can have a better estimate of the full render time. Check it out. http://www.andrewandoru.com/2010/03/17/labs-aerender/ It's just a droplet so you don't even have to open AE and that might help speed up the full render time.
6 hours is a normal time for a project with keying and lots of effects. I had a project that took nearly 14 hours to render once. Intel Core i3 is also not the best processor, so upgrading it would minimize the render time.
As the others said, it's perfectly normal. Sometimes even 10 second stuff can render for 2 hours. In your case it's probably the footage I/O in combination with the not so powerful CPU that makes things slow. I'm sure on anotehr system it would render in half that time...