All PulseAudio source files, except as noted below, are licensed under the GNU Lesser General Public License. (see file LGPL for details)
However, the server side has optional GPL dependencies. These include the libsamplerate and gdbm (core libraries), LIRC (lirc module) and FFTW (equalizer module), although others may also be included in the future. If PulseAudio is compiled with these optional components, this effectively downgrades the license of the server part to GPL (see the file GPL for details), exercising section 3 of the LGPL. In such circumstances, you should treat the client library (libpulse) of PulseAudio as being LGPL licensed and the server part (libpulsecore) as being GPL licensed. Since the PulseAudio daemon, tests, various utilities/helpers and the modules link to libpulsecore and/or the afore mentioned optional GPL dependencies they are of course also GPL licensed also in this scenario.
In addition to this, if D-Bus support is enabled, the PulseAudio client library (libpulse) MAY need to be licensed under the GPL, depending on the license adopted for libdbus. libdbus is licensed under either of the Academic Free License 2.1 or GPL 2.0 or above. Which of these applies is your choice, and the result affects the licensing of libpulse and thus, potentially, all programs that link to libpulse.
Andre Adrian's echo cancellation implementation is licensed under a less restrictive license - see src/modules/echo-cancel/adrian-license.txt for details.
Some other files pulled into PA source (i.e. reference implementations that are considered too small and stable to be considered as an external library) use the more permissive MIT license. These include the device reservation DBus protocol and realtime kit implementations.
A more permissive BSD-style license is used for LFE filters, see src/pulsecore/filter/LICENSE.WEBKIT for details.
Additionally, a more permissive Sun license is used for code that performs u-law, A-law and linear PCM conversions.
While we attempt to provide a summary here, it is the ultimate responsibility of the packager to ensure the components they use in their build of PulseAudio meets their license requirements.