Here is a list of all files with brief descriptions:

include
cdio
audio.h	The top-level header for CD audio-related libcdio calls. These control playing of the CD-ROM through its line-out jack
bytesex.h	Generic Byte-swapping routines
bytesex_asm.h	Assembly code to handle byte-swapping
cd_types.h	Header for routines which automatically determine the Compact Disc format and possibly filesystem on the CD
cdio.h	The top-level header for libcdio: the CD Input and Control library. Applications include this for anything regarding libcdio
cdtext.h	The top-level header for CD-Text information. Applications include this for CD-Text access
device.h	C header for driver- or device-related libcdio calls. ("device" includes CD-image reading devices)
disc.h	The top-level header for disc-related libcdio calls
ds.h	The top-level header for list-related data structures
dvd.h	Definitions for DVD access
ecma_167.h	Definitions based on ECMA-167 3rd edition (June 1997) See http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-167.pdf
iso9660.h	The top-level interface header for libiso9660: the ISO-9660 filesystem library; applications include this
logging.h	Header to control logging and level of detail of output
memory.h	Memory management utility functions
mmc.h	Common definitions for MMC (Multimedia Commands). Applications include this for direct MMC access
mmc_cmds.h	The top-level header for libcdio multi-media commands (MMC)
mmc_hl_cmds.h	Higher-level MMC commands which build on top of the lower-level MMC commands
mmc_ll_cmds.h	Wrappers for specific Multimedia Command (MMC) commands e.g., READ DISC, START/STOP UNIT
mmc_util.h	Multimedia Command (MMC) "helper" routines that don't depend on anything other than headers
posix.h	Various POSIX definitions
read.h	The top-level header for sector (block, frame)-related libcdio calls
rock.h	Things related to the Rock Ridge Interchange Protocol (RRIP)
sector.h	Things related to CD-ROM layout: tracks, sector sizes, MSFs, LBAs
track.h	The top-level header for track-related libcdio calls
types.h	Common type definitions used pervasively in libcdio
udf.h	The top-level interface header for libudf: UDF filesystem library; applications include this
udf_file.h	Routines involving UDF file operations
udf_time.h	UDF time conversion and access files
utf8.h	UTF-8 support
util.h	Miscellaneous utility functions
version.h	A file containing the libcdio package version number (20201) and OS build name
xa.h	Things related to the ISO-9660 XA (Extended Attributes) format