How to export and reimport clips maintaining best quality?

Question

I'd like to ask a few questions.
(1) I have several subclips in FCE that I would like to export, so I can import them back into FCE as individual clips, separate from the original capture. I would also like the option to use the exported clips in iMovie project. The most important thing is to save the clips at the highest possible quality. I ran into a problem when trying to import the clips back into FCE.
First, I tried exporting clips using File>Export>Using Quicktime Conversion... with the following options:
Video Settings:
Compression Type H.264
Quality: Best (the slider in the Settings window I dragged all the way to the right for Best quality)
Key frame rate: 24
Frame Reordering: yes
Encoding mode: multi-pass
Audio Settings:
Format: Uncompressed
Sample rate: 48 kHz
Sample size: 16
Channels: 2
Prepare for Internet Streaming <unchecked>
The clip was saved to disk. I didn't open or modify the clip at all.
Then I tried using File>Import>Files... but when I tried to import it, I got this error:
"File Error: 1 file(s) recognized, 0 access denied, 1 unknown."
So this is the problem I'm experiencing. Can't re-import the clip into FCE (it imports into iMovie fine, though)
Questions: Am I using "wrong" settings? Why is this happening? How can I export and reimport clips while maintaining best video and audio quality?
(2) A couple related questions: Some of my original source video was recorded at 12-bit quality (32 kHz). I know 16-bit is best (48 kHz) but the camera I used came with factory default 12-bit (and as a novice I didn't know to change it until several months later).
So here are my questions.
(a) If I export these clips using audio export settings at 48 kHz instead of 32 kHz, would that cause any problems?
(b) Would those clips then be recognized by FCE and iMovie as having 48 kHz audio even though it was originally recorded at 32 kHz? (I know the quality will be no better, but I've read somewhere that using 32 kHz audio can cause some problems with out-of-sync audio, particularly in iMovie. My hope is the new clip with the 48 kHz audio will circumvent such problems.)
Thanks for any assistance you can provide.
PowerMac G5 Quad 2.5 GHz   Mac OS X (10.4.3)   NVIDIA GeForce 7800GT

Answer 1

TSchneider: Thanks again for your valuable reply. I have a few follow-up questions.
My first set of questions is about rendering audio to 48kHz in the timeline.
Almost immediately you'll notice that FCE has tagged the
entire audio track with a red bar meaning it will
need to be rendered (if you try to play the clip from
the Canvas controls you'll just get beeping or very
low quality sound). Go up to the Sequence menu and
select the Render All (or Mixdown) command and FCE
will transcode the 32kHz audio of your clip to the
48kHz audio of the sequence it's sitting in.
I followed your instructions and everything seemed to work until I got to the passage above. I dragged the subclips into the timeline. The clips appeared in the timeline but there was no red bar. If I chose Render All from the Sequence Menu, nothing happened. If I chose Export to Quicktime Movie, however, it takes several minutes, apparently rendering the audio and video. If I chose instead, Print to Video, the red bars do appear and the rendering process again gets going. There is a small progress bar for both operations in the center of the screen with a percent done and estimated time remaining.
Question: Why doesn't the red bar appear as soon as the clips are in the Timeline?
Question: Why doesn't Render All (or Render Audio) work? It would be much easier to walk away while all the audio rendered into 48kHz and then come back later to save the individual clips to disk.
My second set of questions pertains to the possibility of using Export>Using Quicktime Conversion as a substitute for Export>Quicktime Movie, mainly for academic instead of practical reasons.
If you export a clip directly from the bin "Using
Quicktime Conversion" there aren't any suitable
conversion video/audio formats that would give you
both video in the right format (for iMovie) and
transcode the audio to the sampling rate you want.
I understand your description of rendering the audio files in the timeline. If only academic, I was trying to see if I could duplicate the results using using Export>Using Quicktime Conversion. I chose Quicktime Movie as the format. The video setting was DV/DVCPRO-NTSC. The audio was uncompressed with 48kHz rate. This created a Quicktime movie file with these formats. If I opened the quicktime movie file in Quicktime and checked the info on the file, the audio was indeed 48kHz.
Question: Does this mean that the Quicktime Conversion process rendered the 32kHz audio to 48kHz audio prior to writing the file? If so, it would seem to bypass the need to render the clips in a sequence (although if I could render all the clips in the sequence at once, while I was away from the computer, it would be faster than rendering and saving each clip one at a time).
Question: When I exported a clip this way, then imported it into iMovie, the original capture date/time info was missing when I got info on the clip. However, when I save the clip using Export>Quicktime Movie, the date/time of capture was still present. Would there be any way to preserve this date/time of capture info when using Export>Using Quicktime Conversion?
Question: If I decided to Export>Using Quicktime Conversion with the above settings (DV/DVCPRO-NTSC, 48kHz audio) there are other options I'm given pertaining to the video settings. There are settings for Compressor Quality, with a sliding bar where you can choose Least, Low, Medium, High, and Best quality; and there is Scan Mode (interlaced or progressive). How does one choose among these? If you want the best quality exported clip, I suppose you would chose best quality, but what scan mode is "best" for my purposes -- interlaced or progressive?
Thanks a lot for your help. I'm learning a lot!