13. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving data including (i) audio data that encodes a spoken natural language query, and (ii) environmental audio data; obtaining a transcription of the spoken natural language query; determining a particular content type associated with one or more keywords in the transcription; providing at least a portion of the environmental audio data to a content recognition engine; and identifying a content item that (i) has been output by the content recognition engine, and (ii) matches the particular content type associated with the one or more keywords in the transcription.
13. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving data including (i) audio data that encodes a spoken natural language query, and (ii) environmental audio data; obtaining a transcription of the spoken natural language query; determining a particular content type associated with one or more keywords in the transcription; providing at least a portion of the environmental audio data to a content recognition engine; and identifying a content item that (i) has been output by the content recognition engine, and (ii) matches the particular content type associated with the one or more keywords in the transcription. 17. The system of claim 13 , wherein determining the particular content type further includes identifying the one or more keywords using one or more databases that, for each of multiple content types, maps at least one of the keywords to at least one of the multiple content types.