pyo looked like the best option, but have not tested it.

https://www.google.com/search?q=audio%20speed%20shift%20open%20source%20library&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=np&source=hp#channel=np&fp=b60ef2c46460515a&q=change+audio+playback+speed+library+open+source&rls=org.mozilla:en-US:official&spell=1
change audio playback speed library open source - Google Search
http://www.surina.net/soundtouch/
SoundTouch Sound Processing Library
http://www.surina.net/soundtouch/sourcecode.html
SoundTouch Sound Processing Library
http://stackoverflow.com/questions/15785586/changing-tempo-speed-of-audio
c++ - Changing tempo (speed) of audio - Stack Overflow
http://breakfastquay.com/rubberband/
Rubber Band Audio Time Stretcher Library
http://www.dspdimension.com/technology-licensing/dirac/
DIRAC Time Stretching & Pitch Shifting : The DSP Dimension
http://en.wikipedia.org/wiki/Audio_time-scale/pitch_modification
Audio time-scale/pitch modification - Wikipedia, the free encyclopedia
https://www.google.com/search?q=mixxx&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=fflb#channel=fflb&fp=b60ef2c46460515a&q=mixxx+source+code&rls=org.mozilla:en-US%3Aofficial
mixxx source code - Google Search
http://www.mixxx.org/wiki/doku.php
start [Mixxx Wiki]
http://www.mixxx.org/wiki/doku.php/getting_involved
getting_involved [Mixxx Wiki]
http://mixxx.org/download.php
Mixxx - Download the Best Free MP3 DJ Mixing Software
http://www.oscillicious.com/?utm_source=mixxx&utm_medium=gap_banner&utm_content=frontpage_workinghard&utm_campaign=mixxx
Oscillicious - Delicious Audio Software for Musicians
http://www.oscillicious.com/beatcleaver/sampling-for-mixxx/?utm_source=mixxx&utm_medium=gap_banner&utm_content=frontpage_workinghard&utm_campaign=mixxx
Oscillicious - Slice Beats with BeatCleaver
http://www.jamdeck.net/?utm_source=mixxx&utm_medium=gap_banner&utm_content=frontpage_workinghard&utm_campaign=mixxx
JAMDECK - Organic Music Sketching Software for Windows and Mac
http://bazaar.launchpad.net/~mixxxdevelopers/mixxx/trunk/view/head:/mixxx/README
~mixxxdevelopers/mixxx/trunk : contents of mixxx/README at revision 3430
http://www.mega-nerd.com/libsndfile/
libsndfile
https://www.google.com/search?q=python+time-stretching+pitch-shifting&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=fflb#channel=fflb&fp=b60ef2c46460515a&q=python+audio&rls=org.mozilla:en-US%3Aofficial
python audio - Google Search
http://wiki.python.org/moin/PythonInMusic
PythonInMusic - Python Wiki
http://sndobj.sourceforge.net/
SndObj Library Homepage
http://code.google.com/p/pyo/
pyo - Python digital signal processing module. - Google Project Hosting
http://www.dspdimension.com/download/
Download : The DSP Dimension

http://www.bluegriffon.org/

Bluegriffon is the most up to date version of kompozer I've found recently

http://en.wikipedia.org/wiki/BlueGriffon