Final answer:
In Keynote, media playback is driven by the QuickTime engine, which is an adaptable multimedia framework used across the Apple software ecosystem.
Step-by-step explanation:
The engine that drives media playback in Keynote is QuickTime. Apple's Keynote, part of the iWork suite, uses QuickTime technology for handling various multimedia elements. QuickTime is an extensible multimedia framework capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. It is deeply integrated into Apple's software ecosystem, providing native support for media playback within applications like Keynote.