Beside Nuance, Lumenvox and SpeechPro backends, it supports Pocketsphinx which is amazing and free. The bad side of it is that it's not going to work out of box. The decoder integration is just not done right:
- VAD does not properly strip silence before it pass audio frames to a decoder, because of that accuracy of recognition is essentially zero.
- Decoder configuration is not optimal
- The result is not retrieved as it might be
Also, UniMRCP is not going to work with recent Asterisk releases like 11, it works with 1.6 as far as I see. The new API is not supported.
So, a lot of work is needed to make it actually working and not confusing the users who build their models with CMUSphinx. However, the perspectives are amazing so one might want to spend some time on finalizing Pocketsphinx plugin in UniMRCP. I hope to see it soon.