Overview

Chunk files are files that contain continuous media data with information about the data that would be constructed by file objects preparsed. The motivation to use chunk file formats instead of the original file format is to speed file object creation since it would no longer have to construct the ancilliary information stored with the data in chunk files. Chunk files are created and accessed through routines in cmChunk.c in the CM library (libcm.a). A chunk file consists of one or more chunks of data. Each chunk contains a it's type and length. The basic model of how to use the chunk file routines to access this data is:

There are other commands in the chunk module that allow you to "rewind", write chunks, etc. The various chunk type macros are contained in cmCookies.h and the format of specific chunk file formats for different types of data is described individually in separate pages (see links below).

Currently, the following data formats have chunk file formats associated with them:

  • Motion JPEG
  • MPEG
  • SPARC audio (i.e., .au files)

    Utilities exist from converting from different data formats to the corresponding chunk file formats. These utiltities are briefly described in each of the format description pages found in the links above.