A distinguishing feature of a digital library is that it has Terabyte volumes of multimedia resources. One challenge for researchers in the field of multimedia is to find a testbed for showing the potentials of multimedia technologies such as video summarization, semantic annotation, multimedia cross indexing and retrieval, and etc. Deeper research and wider applications of digital libraries revealed their indispensable role as testbed for multimedia technologies. This paper presents challenging issues of some key techniques used in digital libraries and their specific needs for multimedia technologies.