failed to encode 88 B of PCM data: invalid argument

[CosineP]

Version / OS: master / Debian Testing

Steps to reproduce:
Call sendAudioData with data from PortAudio.

A small 75-line program that demonstrates the problem: https://gist.github.com/CosineP/c2811cd9b7461b05046f15d4ae2f0183

Expected results:
Audio is sent to Mumble server

Actual results:
This fatal AudioException is thrown:

terminate called after throwing an instance of 'mumlib::AudioException'
  what():  failed to encode 69 B of PCM data: invalid argument