The Python module isn't linked against libambulant_ffmpeg, and possibly some other libraries as well.
This isn't a problem when using it from within Ambulant (in a python plugin) because the libraries have been loaded by the Ambulant main program, but it is a problem when using "import ambulant" from a Python main program (missing external references).
Easiest to see on Linux, after doing "make install" for the whole ambulant and then "import ambulant" in Python.
src/pyambulant/Makefile.am should make sure ambulant.so is linked against all the correct libraries, src/player_gtk/Makefile.am can be used as an example.