The sentiment_analysis service can be used to apply sentiment analysis on the audio input. With the use of dialogflow, the sentiment_analysis service can process the audio input given by an user. Making use of a Naive Bayes Classifier, sentiment_analysis can classify a sentence as either being positive or negative. This service is built using the Natural Language Toolkit (NLTK) package from python.
Since this service is still being worked on, it should be noted that this Naive Bayes Classifier is trained on a dataset consisting of 10000 random twitter samples. Therefore, in some cases the service is still performing poorly.