ao_file_extension missing
In libao-1.1.0, the function char* ao_file_extension(int driver_id) is still defined in the header file (ao/ao.h), and it is documented (http://xiph.org/ao/doc/ao_file_extension.html), however the function itself is not present in the library. You can check it by running nm -D -C --defined-only libao.so :
0000000000000000 A LIBAO4_1.1.0
0000000000003440 T ao_append_global_option
0000000000003390 T ao_append_option
0000000000003ab0 T ao_close
0000000000003ba0 T ao_default_driver_id
0000000000003b40 T ao_driver_id
0000000000003db0 T ao_driver_info
0000000000003e10 T ao_driver_info_list
0000000000003460 T ao_free_options
0000000000002fa0 T ao_initialize
0000000000003e20 T ao_is_big_endian
0000000000004bc0 T ao_open_file
0000000000004cb0 T ao_open_live
0000000000003550 T ao_play
00000000000034a0 T ao_shutdownSo, either way there is a problem: either there is a problem in the code, or the documentation and header should be updated.