It turns out that timing of the movie is different in the exported QuickTime video compared to when playing the slideshow in Keynote, if these conditions are met: 1) you have imported video clips on the slides, and 2) you have defined delays on the slides. The solution is to use Play → Record Slideshow to set custom slide timing, which is actually a better and faster process altogether.
- Set up the document. On Document panel, you have two presentation types that are relevant in this context: Normal and Self-Playing. "Normal" is actually the better option, because of the bug above. We used the "16:9" slide size.
- Timing of slides and animations. The only thing you need to care about is the timing of slide transitions and object effects/animations. The rest will be taken care of with Record Slideshow.
- Transition settings: on animating out (leaving slide)
- Importing video clips. We used QuickTime Player to record shots of Weld in action. These clips can then be imported straight into Keynote. Editing tools (Format panel → Movie) are limited: you can change start and end points, but to change the speed of the movie you need to use iMovie. Make sure to disable the "Start movie on click" option.
- Music soundtrack. Music can be added to the presentation (Document panel → Audio). Note that when you preview the presentation, the music always restarts, so play from slide 1 if you want a better understanding of how the music syncs with the slides.
- Animations. Plenty of options both for slide transitions and object animations, but the "Magic Move" transition (Animate panel with nothing selected) is worth mentioning: make a slide with objects laid out, duplicate the slide and rearrange the layout -- Magic Move will "morph" the objects between the two layouts.
- Record Slideshow. When all content is imported and animations/transitions are set up, it's time to set the final timing of the movie. Go into Play → Record Slideshow. Mute the microphone and click the Record button. The music will start playing and you can now advance the movie manually, in sync with the music.
- Export to QuickTime. Export at 1080p resolution and make sure to use the Slideshow Recording playback timing.