The Biblioteca Nacional de España (BNE, the National Library of Spain) is well aware of the dangers facing its audiovisual heritage due to the instability, vulnerability, and degradation of the media on which it is stored. This is so even though the materials are preserved under controlled environmental conditions. For this reason, the library is allocating part of its resources to the digitization of this heritage as a preservation measure. In this paper we outline the main tasks involved. We stress the importance of selecting the material to be digitized, especially in the case of a collection as voluminous as the one belonging to the National Library. We also discuss the difficulties in deciding the formats and digitization parameters, and how these decisions will depend largely on the quality of the originals and the available resources. Lastly, we highlight the importance of recording information in metadata files and the steps that need to be taken to preserve this digital collection in the long term.