I have AECS3 Pro. When I press the 0 for render preview of my work (only still images and audio), AE only previews for 12 seconds, yet my project lasts for 30 seconds. When I press the space bar to play through the timeline, I let in run for say for 25 seconds, I then go into render preview and the render green line at the top of the time line shrinks either side until it can only play 12 seconds of my project.
What am I doing wrong?
You're running out of RAM.
Read up on RAM Previews in the help files to find out more info.
Some solutions would be: