  Captions provide language learners with a scaffold for comprehension and
vocabulary acquisition. Past work has proposed several enhancements such as
keyword highlights for increased learning gains. However, little is known about
learners' experience with enhanced captions, although this is critical for
adoption in everyday life. We conducted a survey and focus group to elicit
learner preferences and requirements and implemented a processing pipeline for
enhanced captions with keyword highlights, time-synchronized keyword
highlights, and keyword captions. A subsequent online study (n = 49) showed
that time-synchronized keyword highlights were the preferred design for
learning but were perceived as too distracting to replace standard captions in
everyday viewing scenarios. We conclude that keyword highlights and
time-synchronization are suitable for integrating learning into an entertaining
everyday-life activity, but the design should be optimized to provide a more
seamless experience.
