Audio recorder - continuous recording but store only last 30 seconds

I have an application where I need to be recording audio continuously to a circular/ring buffer that can store the last 30 seconds of audio at any given time. Upon some event the audio should continue to record for an additional 15 seconds and store it to a file. Also multiple events can be triggered back to back within a few seconds of each other. This case should be considered too. This should be a Linux based application using Qt and probably using QAudioRecoder, QAudioProbe.