It is challenging to conduct quality of experience (QoE) evaluations of web-based streaming video services effectively and efficiently. Aiming to overcome this challenge, we have created QoECenter, a web-based visual platform that innovatively facilitates comprehensive QoE evaluations of the streaming video services. QoECenter offers a holistic approach to conducting the QoE evaluations via an integrated set of technologies for source video classification, QoS realization of video encoding and network transmission, and context-aware user experience data gathering and analysis. From a QoECenter consumer's viewpoint, three kinds of data are required for an end-to-end streaming video QoE evaluation: Video source level data, system process level data, and end user level data. QoECenter provides visual interfaces for parameter setting and data acquisition for each data level, and supports both objective and subjective datadriven QoE analyses. A QoECenter consumer can easily conduct comparative QoE evaluations like running easy-to-use visual applications. The effectiveness and efficiency design objectives of QoECenter have been validated by various real experiments.