Why does some video need to be rendered in FCE 4 before I can work on it?

Question

I've been trying to get a handle on FCE 4 because it's very different than iMovie '08. I have a bunch of content in iMovie that I'd like to mess with in FCE 4, so I exported from iMovie as FCE XML and imported in FCE. There is some video that I re-encoded to Quicktime from ASF and it seems to need to be rendered before it will show up in the Canvas in FCE 4. FCE shows this content as DV/DVCPRO - NTSC under "Compressor" in the browser. Other stuff that was taken off my Sony HDR-SR7 is available in FCE 4 without any problems. This shows up as Apple Intermediate Coded in the browser.
What's the deal with rendering anyway? Why does FCE need to "render" video to add things like effects when iMovie can add effects, etc at will with no "rendering" required?

Answer 1

FCE can do certain effects on the fly without rendering. Some more elaborate transitions, like 3D wipes, require too much processor time to do them in real time. My understanding is that Macs with greater on-board processing power do more of these effects in real time, while slower machines must render.
iMovie can do these effects on the fly because it's working with far less information. Think of iMovie works in the DV format while FCE works in the DV/DVCPRO-NTSC format. It's too subtle a name difference but the reality is quite different. It's like editing still pictures in compressed, lossy JPEG format vs. uncompressed TIFF format. Think about how long it takes your computer to open a photo of say, 8x10" 300 dpi in TIFF vs. that same file in JPEG. Well, that's what FCE has to do. It's working in the video equivalent of TIFF -- 30 frames per second. So there's a greater demand on your processor by a factor of 10. You can see this in action in Quicktime. Save a raw video import 720x480 in .dv and then in DV/DVCPRO-NTSC format and then play it back. The .dv will probably play smoothly while the DV/DVCPRO-NTSC (.mov) will hang up on play-back. It's just too much for your process to display all of those full resolution images so rapidly. And if you look at the two images side-by-side (particularly titles) you'll see how sharp and clear the .mov file is compared to the compressed .dv file.
Hope this helps.