Avoid Rendering in Final Cut Pro: Smaller Frame Size? I usually have great success in not needing rendering. I take all of my clips and make them Apple ProRes 422 @29.97fps and everything works. The clip that defines the characteristics of the sequence is imported from AVCHD, so it's Apple ProRes 422 1920x1080 @29.97fps (HDTV 1080i).

Today, one of my clips wants to be 1024x768 @29.97fps and the sequence (and other clips) are HDTV 1080i @29.97. For some reason, the smaller frame-size clip needs rendering. If I use Mpeg Streamclip and scale it up (to 720p, for instance), then it doesn't need rendering. However, I want it in its actual size (1024x768).

I've been through this before and was able to use clips that were not 1920x1080 with success. This time, I need to render. What am I doing wrong?
First off, there is no such coded as ProRes 411, so I have to assume you are using ProRes 422...which is a great start.

However it is not really worth the effort of trying to convert the clips so that you don't have to render within Final Cut, rendering in Final Cut is going to occur whether you attempt to avoid it or not.  In your case I believe it is a difference in pixel aspect ratio, if the PAR matches with a different frame size typically you do not have to render, however if they do not match even if both clips are 1920x1080 you would still need to render.