Using libextractor, you can extract metadata from files of arbitrary
types. Supported file formats include HTML, PDF, DVI, PS, MP3, OGG,
WAV, JPEG, GIF, PNG, TIFF, RPM, ZIP, TAR, ELF, REAL, RIFF (AVI), MPEG,
QT, and ASF. Also, various additional MIME types are detected.

Helper libraries perform the extraction. It is extendable by linking
against external extractors for additional file types.

The goal is to provide developers of indexing tools with a universal
library to obtain simple keywords to match against queries.
libextractor contains a shell command "extract" that, similar to the
well-known "file" command, can extract metadata from a file and print
the results to stdout.