i was getting this error while trying to compile faad2:

configure.in:14: error: possibly undefined macro: AC_PROG_LIBTOOL
If this token and others are legitimate, please use m4_pattern_allow.
See the Autoconf documentation.
autoreconf: /usr/bin/autoconf failed with exit status: 1

i made this error go away by install “libtool:”

$ sudo apt-get install libtool