convert .mov to mp3

Welcome to the Apple Support Communities!
I understand you are looking to convert a .mov file to .mp3. The MP3 format is for audio only, so the best way to accomplish this is to open the video application you used to create the project, and export just the audio. I've highlighted some key information here for you. Click on the link for complete details.

iMovie Help - Export a QuickTime file

1. Select a movie, trailer, or clipin the browser.

2. Click the Share button in the toolbar, and then click File.

3. Set the output format of the shared movie: Click the Format pop-up menu and choose an option.

   You can choose to export video and audio, or just audio.
   
   

Take care.

Which Mac system are you running on your computer? The version you list in your profile is quite old and may call for a different solution. The best solution may also depend upon how this mov file was created and how important it is to you to preserve the original quality.