PhysicsFS is a library to provide abstract access to various archives. The programmer defines a "write directory" on the physical filesystem. No file writing done through the PhysicsFS API can leave that write directory, for security. For file reading, the programmer lists directories and archives that form a "search path". Once the search path is defined, it becomes a single, transparent, hierarchical filesystem. This makes for easy access to ZIP files in the same way as you access a file directly on the disk, and it makes it easy to ship a new archive that will override a previous archive on a per-file basis. Symbolic links can be disabled, for added safety. Finally, PhysicsFS gives you a platform- abstracted means to determine if CD-ROMs are available, the user's home directory, where in the real filesystem your program is running, etc.
SDL_sound is a library that handles the decoding of several popular sound file formats such as .WAV and .MP3. Designed to make the task of sound playback easier, SDL_sound accepts files or other input through an abstraction layer and returns the decoded waveform. SDL_sound can decode a whole sound file and hand back a single pointer to the waveform, or SDL_sound can process sound data in programmer-specified blocks when resource constraints are a concern. SDL_sound can also handle sample rate, audio format, and channel conversion on-the-fly.
Some thoughts from the author... ...okay, okay. The versioning joke was lame. I'm sorry. :) In my next life, I'll be sure to point out that while highly-trusted applications (like Enlightenme...