Consider env vars for ffmpeg path.

README.md

@@ -55,7 +55,7 @@ If you are interested in helping, please raise an issue before making any pull r
 - Add a `Photo.merge` to combine duplicate entries.
 - Generate thumbnails for vector files without falling victim to bombs.
 - Allow photos to have nonstandard, orderby-able properties like "release year". How?
-- Make the FFmpeg path configurable. Some kind of global config? Or part of the database config file? It's not like every photodb needs a separate one.
+- Make the FFmpeg path configurable. Some kind of global config? Or part of the database config file? It's not like every photodb needs a separate one. I don't like using environment variables for application config but maybe it would be appropriate here.
 - Improve the appearance of album page. Too many section headers and the "Create album" interface should allow giving a title immediately.
 - When users have '%' or '#', etc. in their username, it is difficult to access their /user/ URL. I would prefer to fix it without simply blacklisting those characters.
 - Currently, the Jinja templates are having a tangling influence on the backend objects, because Jinja cannot import my other modules like bytestring, but it can access the methods of the objects I pass into the template. As a result, the objects have excess helper methods. Consider making them into Jinja filters instead. Which is also kind of ugly but will move that pollution out of the backend at least.