ISO/IEC 14496-23:2008 specifies Symbolic Music Representation (SMR). A symbolic representation of music is a logical structure based on: symbolic elements representing audiovisual events, the relationship between those events, and aspects related to how those events can be rendered (visually as music notation or audibly) and synchronized with other media types.
ANSI/INCITS/ISO/IEC 14496-23:2009 history
2009ANSI/INCITS/ISO/IEC 14496-23:2009 Information technology - Coding of audio-visual objects - Part 23: Symbolic Music Representation