So I'm LOVING the mercury engine playback with Premiere CS5. What I don't like is when I right click a clip on the timeline and "Replace with After Effects Composition" to do some special effects. When I'm done doing what I need to do in AE and switch over to PP to see the changes update, the playback for that particular clip is SLOW AS MOLASSES!! But the timeline is still yellow. Why isn't it red? Also, I can't seem to render it to playback in realtime as I am editing a music video. Am I missing something here? I have a CUDA enabled card, 12 gigs of Ram, and a Quad core processor
Yeah, the yellow bar is a little misleading with AE comps--but the performance you're seeing is, depending on the complexity of the comp and the effects you're using in AE, perfectly normal. Even in AE, the only way you can get real-time playback with anything but the most basic composition is to render a RAM Preview. So even though you have a yellow bar over the comp when it's in your PPro sequence, it's highly unlikely you'll get real-time playback in Premiere. That's why you'd typically save these steps until close to the end of your project, when you're done editing. There's a reason it's called "After Effects"
Anyway, the workaround is to force a preview render in Premiere. Just mark the section you want rendered (yellow bar and/or red bar), and go to Sequence > Render Entire Work Area. Unlike the "Render Effects in Work Area" command (or pressing the Enter key), this will create preview files for anything that has a red or yellow bar above it.