how can I export a photo booth video to an email

Right-Click on the icon for the movie in the tray at the bottom of the window and select 'Export' to get it out of Photobooth to the Finder. However, sharing video via email is not advisable.

Many email services have an attachment limit of 20mb and some a limit of 10mb. As emails are sent through an array of relays, the effective limit is the smallest file size allowed on any of the relays. That means that video is rarely suitable for emailing.

Then there's the whole issue of Codecs and not all machines will have the codecs to play all videos. Plus, folks with slower connections can find it very inconvenient to download large video files.

Other than that your options include:

Upload it to a sharing site like YouTube or Vimeo and email a link - these will allow the recipient to view the material online. That will avoid the codec issues mentions, and the person can still download the video file if they wish.

Upload it to sharing services like Dropbox or YouSendIt and email a link. This will require that they download the material to their machines to view.

Regards

TD