This document describes a vendor-neutral subset of the MXF file format to use for the long-term archiving and preservation of moving image and other audiovisual content, including all forms of Ancillary Data, together with Associated Materials. Among other features, RDD 48 defines a means for the carriage and labeling of multiple timecodes; the handling of captions, subtitles, and Timed Text; a minimal core metadata set; program segmentation metadata; and embedded content integrity data. - RDD 48 files may contain a single item, or an entire series of items. - RDD 48 files are not intended for direct online access; however they may include renditions intended for viewing without further processing. - RDD 48 files are intended to be used in combination with external finding aids or catalog records. The external finding aids are used for day to day access to the archive collection. At the same time, RDD 48 files must stand alone, so they would retain their value even if they were the only extant copy of an item. - Derivative versions of RDD 48 will be developed over time. Prior to 2016, AMWA referred to these as shims, and that term is used in this document, reflecting the fact that it was initially drafted in 2014-15. In this version, the Baseband Shim specified in annex J is an important element. This derivative version is intended to serve the most critical current use case for memory institutions: the reformatting of existing and obsolescent videotapes in their collections. The Baseband Shim is also intended to serve memory institutions (and others) who may be acquiring digital video ingested via serial interfaces, e.g., congressional high definition video transferred to the Library of Congress via HD-SDI or its equivalent. In both of these use cases, memory institutions wish to archive the highest possible quality of image and sound (uncompressed or losslessly compressed), as well as retaining source data such as multiple timecodes, captions and subtitles, and also embed metadata that will support authentication and management of the content for the long term.