Mixing HD and SD videos

Hi, I'm new to the forum and to FCPX. I produce family genealogy and "life story" videos, and I hope someone can answer a question for me.

If I use two cameras, one recording HD and the other recording SD, can I use the video from both cameras to produce a recording that retains the HD quality on those portions of the video?

Or asked another way, if the first clip in my finished video is shot in HD, does that set the parameter of the entire video, so that all my HD video shows up as HD, even if there are also some SD clips in the the video?

Thanks for any guidance or answers you can provide.

Yes, by adding an HD clip to your project timeline first you'll be insuring that your video will have the same dimensions, assuming that when you created the project you chose "Set based on first video clip" for your Video Properties.

Thanks timfo. I do have my projects set to use the properties from the first clip. 90% of the clips I use will come from my HD camera, but I wanted to make sure there wasn't something in FCPX that would try to downgrade my resolution to the "lowest common denominator".