If present in any quantity, treat audiovisual material as a separate series (with necessary cross-references to related paper files, as appropriate). If there is a substantial quantity of various formats, subseries may be established by format. Otherwise, isolated instances can be interfiled intellectually in existing non-format-specific series (an intellectual arrangement by writing or project might supersede a format-driven arrangement).
Depending on the level of processing, audiovisual material might be arranged at the item level and housed in a single folder or many items will be described at the box level. A single item per folder approach will simplify updates when material is digitized and provides a consistent approach to physical arrangement in larger collections.