To create visually engaging subtitles in iMovie you're going to have to transcribe your piece of audio manually first.
If your audio is really clean you could popuparchive.com to get it automatically transcribed for free but the results are not always very good.
Once you've transcribed your audio, you're ready to start creating some nice subtitles in iMovie.
- Add just the audio of your teaser promo clip to a new iMovie
2. Select "Titles" at the top and choose an animation template that you would like to use. In this example I've chosen "pop-up" and drag it into the timeline window:
3. To change the text and font, double-click the purple section and your text-box will become highlighted.
4. Time the display length of each piece of text by carefully dragging each text box left and right so that it syncs up with the audio. Repeat this process until your whole clip has been annotated. Finally, click backgrounds, select a background you would like to use and change the opacity of that background so that your text shows through.
5. Upload and share away!