scaletempo: add mode for speech speed algorithm from libsonic
Submitted by Frédéric Wang
Link to original bug (#744062)
Description
I'm opening this bug as I plan to create a plugin for libsonic:
https://raw.githubusercontent.com/waywardgeek/sonic/master/README
For now, the closest I found is the "scaletempo" element (WSOLA/SoundTouch). Here is how Sonic's author compares his algorithm with WSOLA/SoundTouch:
https://github.com/waywardgeek/sonic/blob/master/doc/index.md#comparison-to-other-solutions