git-annex's [[metadata]] works best when files have a lot of useful
metadata attached to them.

To make git-annex automatically set the year and month when adding files,
run `git config annex.genmetadata true`.

A git commit hook can be set up to extract lots of metadata from files
like photos, mp3s, etc.

* Install the `extract` utility, from <http://www.gnu.org/software/libextractor/>  
  `apt-get install extract`
* Download [[pre-commit-annex]] and install it in your git-annex repository
  as `.git/hooks/pre-commit-annex`.  
  Remember to make the script executable!
* Run: `git config metadata.extract "artist album title camera_make video_dimensions"`

Now any fields you list in metadata.extract to will be extracted and
stored when files are committed.

To get a list of all possible fields, run: `extract -L | sed ' ' _`

By default, if a git-annex already has a metadata field for a file,
its value will not be overwritten with metadata taken from files.
To allow overwriting, run: `git config metadata.overwrite true`