Libspeex

speex and speexdsp

Speex is an Open Source/Free Software patent-free audio compression format
designed for speech. The Speex Project aims to lower the barrier of entry for
voice applications by providing a free alternative to expensive proprietary
speech codecs. Moreover, Speex is well-adapted to Internet applications and
provides useful features that are not present in most other codecs. Finally,
Speex is part of the GNU Project and is available under the revised BSD license.

Speex is based on CELP and is designed to compress voice at bitrates ranging
from 2 to 44 kbps. Some of Speex's features include:

    Narrowband (8 kHz), wideband (16 kHz), and ultra-wideband (32 kHz)
compression in the same bitstream
    Intensity stereo encoding
    Packet loss concealment
    Variable bitrate operation (VBR)
    Voice Activity Detection (VAD)
    Discontinuous Transmission (DTX)
    Fixed-point port
    Acoustic echo canceller
    Noise suppression

Note that Speex has a number of features that are not present in other codecs,
such as intensity stereo encoding, integration of multiple sampling rates in the
same bitstream (embedded coding), and a VBR mode.