For stable versions of Inkscape, you can download the code and read the installation instructions on github:
Download (.zip) https://github.com/nikitakit/svg2sif/zipball/stable
Download (.tar.gz) https://github.com/nikitakit/svg2sif/tarball/stable
Github page / Installation Instructions: https://github.com/nikitakit/svg2sif
(If you're using Inkscape nightly builds or building Inkscape trunk yourself the extension should be installed automatically.)
Inkscape writes out SIF files within the following constraints:
- It's designed to work with Inkscape-created SVG files. SVG files loaded from other programs may not work as well
- Blurs don't transfer over one-to-one. The resulting SIF file may need to be hand-edited to make the blurs stronger or weaker
- SVG filters are ignored. They do not port easily to Synfig, and some can't be converted at all.
- Radial gradients with focus not at the center are not allowed. The Synfig renderer does not support them.
- Dashed outlines, markers, and patterns are ignored. If you need them, post a feature request.
All SVG files falling within these constraints are fair game -- if they don't work, leave a comment here and I'll try to fix the problem.
If everything works as expected, please post a reply as well. I would like to know how many people have tested it and what setups they use.