This is mainly so that I don't forget how to export my Flash animations properly, but hopefully this will save someone else some time too.
1. Create your Flash project at 640*480px and 24fps.
2. File => Export => Movie.
3. Save type as Quicktime (*.mov)
4. Go to "Quicktime Settings..."
5. I unchecked "Sound" as, although there is sound in the Flash project, it was only used to check timing and it is easier to manipulate sound later in Premier. Then go to "Settings..."
6. Set the frame rate to "24" fps, key frames to "All", Depth to "Millions of Colours+"and Quality to "Best".
7. Set up the Premier project at "DV - 24p Standard 48kHz". Import the flash .mov and sound (mp3 seemed to be fine for me).
8. When you are ready to export the video: "File => Export => Media ". Set the format to "H.264" and preset to "NTSC DV". I found it useful to modify the output name so that it describes the export settings. It made it a lot easier to work out which settings produce the best quality and file sizes.
9. The export for the video will now look ok, but will have thin black bars on each side, to get rid of this, but also remove a thin slice from the top and bottom of the frame, set the source scaling to "Scale to Fill".
10. Then upload your video, I was using Vimeo, but I am sure the quality and file size will be fine for Youtube.
