An audio/video generation apparatus comprises an audio and/or video generation device operable to generate audio and/or video material, and a metadata generation processor. The metadata generation processor is operable to generate metadata describing the content and/or attributes of the audio/video material. The metadata generation processor is operable to generate a reference value providing a quasi-unique reference to the audio/video material with a reduced amount of data with respect to the audio/video material itself, the reference value being generated from data values representing the audio/video material in accordance with a predetermined relationship. The quasi-unique reference may be stored in association with the metadata describing the audio/video material from which the quasi-unique reference was generated.Generating a quasi-unique reference from the information material provides a facility for identifying the audio/video material. In one embodiment the quasi-unique reference is a hash value. The hash value provides a quasi-unique reference, which can be efficiently searched in order to identify, the audio/video material. Accordingly, metadata, which describes the content or attributes of the audio/video material, may be uniquely or quasi uniquely associated with the information material.