As the device holding great promise to realize the vision of pervasive computing, smartphones with Internet access and video playing capability have become commercial off the shelf products today As one of the most popular applications on smartphones, online video playing, however, still faces some problems From the perspective of service providers, they have to provide video files of different formats and qualities to meet the diverse needs of various consumers From the perspective of service consumers, if one or more codecs required to open a video file supplied by a certain service provider are not available on their smartphones, they just cannot watch that video or have to install new codecs - both cases give users bad experience To deal with such a situation, this paper puts forward a context-aware approach for online video playing based on cloud computing Our experience demonstrates that the combination of cloud computing and smartphones creates a lot of new opportunities for more advanced services.