ISOBMFF

ISOBMFF stands for ISO Base Media File Format. It is a container format defined by ISO/IEC 14496-12 that provides a generic, extensible structure for storing time-based multimedia data in a single file. The format is designed to support efficient random access, streaming, and the inclusion of both media data and metadata within a unified file layout. It serves as the foundation for a family of media containers used in various multimedia applications.

The file is organized as a hierarchy of boxes (also called atoms). Each box begins with a 4-byte size and a 4-byte type, and larger files may use an extended size. The top-level boxes most often encountered are ftyp (file type), moov (the movie container), and mdat (the media data). The ftyp box declares the major brand and compatible brands, guiding how the file should be interpreted. The moov box contains metadata, such as the movie header and track information, while mdat stores the actual media samples. Additional boxes provide timing, sample descriptions, indexing, and metadata necessary for playback and editing.

ISOBMFF is the base container for the MP4 family of formats. MP4, M4A, and M4V files are typically ISOBMFF containers that carry one or more media tracks described by the format’s box structure. It is also used by 3GPP and 3G2 containers, and, in other contexts, by HEIF for still images, which reuse the same box-based layout. The standard’s design emphasizes interoperability, extensibility, and the ability to support evolving codecs and metadata schemes.