A system to insert supplemental audio content into primary audio content via digital assistant applications, comprising: a record indexer component executed on a data processing system having one or more processors to maintain, on a database, an audio recording of a content publisher and a content spot marker set by the content publisher to specify a content spot that defines a time at which to insert supplemental audio content during presentation of the audio recording; a natural language processor component executed on the data processing system to: receive an audio data packet including an input audio signal that is detected via a microphone of a client device; parse the input audio signal from the audio data packet to determine that the input audio signal corresponds to a request for the audio recording from the content publisher; and identify, based on the request determined from the input audio signal, the audio recording of the content publisher from the database; a content placement component executed on the data processing system to: identify, responsive to the determination that the input audio signal corresponds to the request for the audio recording, an identifier associated with the client device as a content selection parameter; and select, for the content spot of the audio recording, an audio content item of a content provider from a plurality of audio content items using the content selection parameter; and an action handler component executed on the data processing system to: insert the audio content item into the content spot of the audio recording specified by the content spot marker; generate an action data structure including the audio recording inserted with audio content item at the time defined by the content spot marker; and transmit the action data structure to the client device to present the audio recording inserted with the audio content item at the content spot. a record indexer component executed on a data processing system having one or more processors to maintain, on a database, an audio recording of a content publisher and a content spot marker set by the content publisher to specify a content spot that defines a time at which to insert supplemental audio content during presentation of the audio recording; a natural language processor component executed on the data processing system to: receive an audio data packet including an input audio signal that is detected via a microphone of a client device; parse the input audio signal from the audio data packet to determine that the input audio signal corresponds to a request for the audio recording from the content publisher; and identify, based on the request determined from the input audio signal, the audio recording of the content publisher from the database; receive an audio data packet including an input audio signal that is detected via a microphone of a client device; parse the input audio signal from the audio data packet to determine that the input audio signal corresponds to a request for the audio recording from the content publisher; and identify, based on the request determined from the input audio signal, the audio recording of the content publisher from the database; a content placement component executed on the data processing system to: identify, responsive to the determination that the input audio signal corresponds to the request for the audio recording, an identifier associated with the client device as a content selection parameter; and select, for the content spot of the audio recording, an audio content item of a content provider from a plurality of audio content items using the content selection parameter; and identify, responsive to the determination that the input audio signal corresponds to the request for the audio recording, an identifier associated with the client device as a content selection parameter; and select, for the content spot of the audio recording, an audio content item of a content provider from a plurality of audio content items using the content selection parameter; and an action handler component executed on the data processing system to: insert the audio content item into the content spot of the audio recording specified by the content spot marker; generate an action data structure including the audio recording inserted with audio content item at the time defined by the content spot marker; and transmit the action data structure to the client device to present the audio recording inserted with the audio content item at the content spot. insert the audio content item into the content spot of the audio recording specified by the content spot marker; generate an action data structure including the audio recording inserted with audio content item at the time defined by the content spot marker; and transmit the action data structure to the client device to present the audio recording inserted with the audio content item at the content spot.