Since iMovie 11 now support export 1080 Full HD video, also YouTube upload limitations will scale the video to 1080p, 720p pixels there is no point to export it at a larger size. Better to apply higher quality settings to your file size limit, which is 100 megabytes set by Youtube.
I am assuming your video has been edited and is ready for export. Follow these steps to have a video that you can upload with confidence to YouTube.
Part 1: Choosing the best settings for iMovie when exporting for YouTube:
Under the main menu click the Share menu option.
Choose the Share option at the bottom of the drop down menu.
The next window will allow you select from a popup menu. It is labeled “Compress movie for:”. You will chose Expert Settings. Click the share Share button in the bottom right.
The next window will allow you to choose where to save the video and what to name it. At the bottom of the window you will see a popup menu labeled Export. Choose the “Movie to MPEG-4″option.
Click the Option…tton to the right to choose specific video and audio settings.
In this window choose the following setting under the video choices.
Click the OK button and in the next window click the Save button and wait for your high quality video to export.
Part 2: Upload to YouTube
Save your movie to the desktop or somewhere else. Find your movie and click it once then press apple+I to get its information. Make sure it is less than 100 megabytes or YouTube will accept it.
5. Log in to YouTube and click on the “upload” button at the top of the page.
6. Enter the name, category, tags and any other information you want for your video.
7. Next click on “upload a video” once you have finished entering your videos information.
Related: Hw to burn to DVD from iMovie on Mac.