1. A system, comprising: a command service configured to: communicate with multiple applications, communicate with an audio device, and send a command to the audio device to perform an activity for an audio application that provides audio content to be played by the audio device, wherein the command specifies an application identifier corresponding to the audio application; control logic configured to perform acts comprising: receiving an event message from the audio device regarding sound played by the audio device, wherein the event message specifies the application identifier corresponding to the audio application; if the event message indicates that the sound played by the audio device is part of a speech interaction with a user, designating the audio application as being primarily active; if the event message indicates that the sound played by the audio device is not part of a speech interaction with a user, designating the audio application as being secondarily active; a speech recognition service configured to receive an audio signal from the audio device and to recognize user speech in the audio signal; a language understanding service configured to determine a meaning of the user speech; the control logic being configured to perform further actions comprising: if there is a primarily active application among the multiple applications, requesting that the primarily active application respond to the user speech by (a) performing a first action that is indicated at least in part by the meaning of the user speech or (b) generating a first speech response to the user speech; and if there is no primarily active application among the multiple applications and if there is a secondarily active application among the multiple applications, requesting that the secondarily active application respond to the user speech by (a) performing a second action that is indicated at least in part by the meaning of the user speech or (b) generating a second speech response to the user speech.
1. A system, comprising: a command service configured to: communicate with multiple applications, communicate with an audio device, and send a command to the audio device to perform an activity for an audio application that provides audio content to be played by the audio device, wherein the command specifies an application identifier corresponding to the audio application; control logic configured to perform acts comprising: receiving an event message from the audio device regarding sound played by the audio device, wherein the event message specifies the application identifier corresponding to the audio application; if the event message indicates that the sound played by the audio device is part of a speech interaction with a user, designating the audio application as being primarily active; if the event message indicates that the sound played by the audio device is not part of a speech interaction with a user, designating the audio application as being secondarily active; a speech recognition service configured to receive an audio signal from the audio device and to recognize user speech in the audio signal; a language understanding service configured to determine a meaning of the user speech; the control logic being configured to perform further actions comprising: if there is a primarily active application among the multiple applications, requesting that the primarily active application respond to the user speech by (a) performing a first action that is indicated at least in part by the meaning of the user speech or (b) generating a first speech response to the user speech; and if there is no primarily active application among the multiple applications and if there is a secondarily active application among the multiple applications, requesting that the secondarily active application respond to the user speech by (a) performing a second action that is indicated at least in part by the meaning of the user speech or (b) generating a second speech response to the user speech. 4. The system of claim 1 , the actions further comprising: determining that no event message identifying the audio application has been received for a predefined time period; and removing the designation of the audio application being primarily active.