I would explain the ins and outs but unfortunately there are 100s of pages of explanation to answer it fully.
Read this for a basic understanding of what a CODEC (COmpressor-DECompressor, COder-DECoder, or COmpression/DECompression algorithm) is here: [
en.wikipedia.org]
This for DV: [
en.wikipedia.org]
This for Animation: [
en.wikipedia.org]
This for a variety of video CODECs: [
en.wikipedia.org]
Most Video CODECs do not have a specific pixel size but rather give you options to change it to your preference.
Audio CODECs too have various settings.
You need to check exactly what settings you require and set it up in before or during the menu stage of your export.
Ben
For instant answers to more than one hundred common FCP questions, check out the LAFCPUG FAQ Wiki here : [www.lafcpug.org]