

Time-based effects like echo are big RAM hogs, you may have to pre-render layers with these applied. One way is to pre-render sub-comps, another is to make sure images you use are appropriately sized for the output. Check on the available RAM at render time, and if it's getting full you need to take steps to reduce your memory usage.

Is the computer hitting the limits of available memory? This will exponentially slow things down.When those frames have to be rendered first it adds an extra drain on resources, particularly memory.

Rendering to h.264 involves referencing multiple frames to create the intermediate frames.
