File size depends on but two things: Duration, and Bit-Rate. It is likely that your Bit-Rate, for the Share/Export is higher than the orignal files.
Now, choice of CODEC can have an impact, as some allow for higher perceived quality at lower Bit-Rates, but it is still the Duration, and the Bit-Rate that dictate file sizes.
Also, if one starts with heavily-compressed material, but then output to lower-compression scheme, the file sizes will get larger, due to a Bit-Rate difference.
Good luck, and hope that helps,
DV input generates always huge files : 12 Gb/hour is the normal size, so your 4Gb for 20 minutes of video seems OK.
I think QuickTime is the container, it does not change the input format to insure the maximum of quality.
When you compare with HD format, there is differences in terms of codec and coding : the best format, MP4, needs
less space to store videos, and needs powerfull processors to manage it.
Poiisibilities to optimize, in my opinion :
- you can export (or share in PREL) in formats like FLV
- you can convert the input files by using free converters like MPEGStream clip to generate input in MP4. I sometimes
use this technique to change MJPEG input to MP4, in PREL environment, with less disk usage.
- you can convert only the outputfile when editing is finished, so less time to convert.
It also helps to know what you're outputting your files for. There are dozens of optimized formats, depending on how you plan to deliver the video to your viewers.
Do you plan to share it online? Post it to Facebook or YouTube? Do you plan to use it in another video project? Do you plan to burn it to a BluRay or DVD? Output it to an iPod or iPad or smartphone?
As JM and Bill point out, a Quicktime file is not a single file type but a format "package" file which can use any of countless codecs and compression levels, depending on the purpose of the file.
As we often say, you need to start at the end to get to the beginning.