Animated GIFs are transcoded to AVC because it is much smaller and
thus also suitable for long/large animations. In addition, this commit
adds support for more metadata fields such as frame rate, number of
frames, file capture timestamp (unix milliseconds), media type,
and software version. Support for SVG files can later be implemented in
a similar way.
Other color profiles and file formats are not supported yet. Should
be easy to add though. Main difficulty will be profile name comparison:
For example "Adobe RGB (1998)" vs just "Adobe RGB".
