With the technological advancements in computing and networking today, many interesting and potentially useful applications are being developed and turned into products. Digital video is one of those application areas that is getting more and more attention as the consumer market is likely to be huge, including professional video editing and home entertainment. However, most digital video systems so far have been developed based on technologically based ideas and possibilities, thus providing very little usability and poorly designed user interfaces. Having no long-term user base or usage context make it difficult to develop a new system using a user-oriented methodology where a target usage specification is made and a system developed accordingly. In this research, the design of user interface to a digital video system is studied in depth, particularly focusing on keyframe-based video content browsing interfaces. By analysing and identifying important elements in designing keyframe-based browsing interfaces, we construct a welldefined "design space" where a specific user interface can be designed by simply selecting a set of available options. This analytic approach makes the user interface design, which can be difficult to clarify due to its fuzzy nature, much more systematic and manageable. The usefulness of the constructed design space is demonstrated in the context of diverse devices such as desktop PCs and PDAs (Personal Digital Assistants) sharing the same data, and also diverse characteristics of the users. Specifically, video browsers suitable for a PDA are designed, and also various video browsers supporting different user preferences are designed and implemented using the design space. A qualitative evaluation is conducted on the designed browsing interfaces, to improve their usability and to gain further insights into the design of such browsers and refine the underlying design space.