See INSTALL file for instruction on how to install Speex.

The Speex project aims to build an open-source patent-free voice codec. 
Unlike other codecs like MP3 and Ogg Vorbis, Speex is specially designed 
for compressing voice at low bit-rates for applications such as voice over 
IP (VoIP). In some sense, it is meant to be complementary to the Ogg 
Vorbis codec.

Although we aim at providing a patent-free codec, we strongly suggest you
have a look at patent issues if you are thinking of using Speex 
commercially. The speech coding field is a real patent mine field and
the scope and enforceability of all these patents is sometimes unclear,
not to mention that each country has different laws.