RMID is an abbreviation for RIFF-based MIDI File Format. RMID is a wrapper format for MIDI data, as first specified by Microsoft, and later extended by MIDI.org (an arm of the MIDI Manufacturers Association) to permit the bundling of both MIDI files (SMF) and Downloadable Sounds (DLS) files.
Standard MIDI Files (SMF) have been in common use for a number of years. Downloadable Sounds (DLS) files are now becoming popular. However, there is no standard means for bundling a Standard MIDI File together with the DLS data, which should be used to render the file. The RMID format, with appropriate extensions, is the MMA recommended solution for this basic need. The extended RMID format is only intended to contain a single SMF data image, a single DLS data image, plus supplemental data such as version stamp, copyright notice and other descriptive information. In this sense, an extended RMID file will be used simply for portability of linear music just like a General MIDI file except that authors can define their own instruments.
RMID is a standard RIFF file format, originally defined in the Microsoft Multimedia Programmers Reference. RIFF is very similar to IFF, an earlier file metaformat used as the basis for AIFF and many other formats. RIFF (Resource Interchange File Format) is a tagged file structure for multimedia resource files. Strictly speaking, RIFF is not a file format, but a file structure that defines a class of more specific file formats, some of which are listed here as subtypes. The basic building block of a RIFF file is called a chunk. Chunks are identified by four-character codes and an application such as a viewer will skip chunks with codes it does not recognize. The basic chunk is a RIFF chunk, which must start with a second four-character code, a label that identifies the particular RIFF “form” or subtype. Applications that play or render RIFF files may ignore chunks with labels they do not recognize. Chunks can be nested. The RIFF structure is the basis for a few important file formats, but has not been used as the wrapper structure for any file formats developed since the mid 1990s.