The present disclosure is generally related to inserting supplemental audio content into primary audio content via digital assistant applications. A data processing system can maintain an audio recording of a content publisher and a content spot marker to specify a content spot that defines a time at which to insert supplemental audio content. The data processing system can receive an input audio signal from a client device. The data processing system can parse the input audio signal to determine that the input audio signal corresponds to a request and can identify the audio recording of the content publisher. The data processing system can identify, responsive to the determination, a content selection parameter. The data processing system can select an audio content item using the content selection parameter. The data processing system can generate and transmit an action data structure including the audio recording inserted with audio content item.