Default Audio Endpoint Selection in Windows 7 March 30, 2010


Endpoint Timestamp Property Creation and Update on Windows 7



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Endpoint Timestamp Property Creation and Update on Windows 7


In Windows 7, an endpoint’s timestamp property is created or updated only when it is specifically set as the default audio endpoint through the Control Panel Sound application. The basic default device selection operation is similar to that of Windows Vista, but as shown in the following screen shot, a new Set as Default Communications Device option was added.

The new Communications device role was added in Windows 7 to help communication-centric applications provide a better communication experience for device selection. To support this new role, each endpoint now has a separate timestamp property for each device role, as follows:



  • When the end user selects Set Default Device for an endpoint, the audio subsystem creates or updates the timestamp property for the default Console device role.

  • When the end user selects Set as Default Communications Device for an endpoint, the audio subsystem creates or updates the Communications timestamp.

With this new flexibility, different device roles can be set to different audio devices.

To accommodate these changes, the following modified algorithm describes how Windows 7 determines a default audio endpoint for any specific role:


  • The audio subsystem loops through all the ACTIVE endpoints with a matching device role to find the endpoint with the most recent timestamp property. The timestamp property indicates the last time an endpoint was set as the default audio endpoint.

  • If such an audio endpoint is found, it is returned as the default audio endpoint.

  • Otherwise, the audio subsystem resorts to the system default audio endpoint heuristic algorithm to determine the default audio endpoint.

Support for SetupPreferredAudioDevices was removed from Windows 7 because of the following non-deterministic nature:



  • Although each physical audio device can expose multiple audio features or endpoints (such as a microphone, a speaker, and a headphone), SetupPreferredAudioDevices does not allow control at the audio endpoint level.

  • The default audio endpoint settings that result from this INF directive are affected by the order in which its driver exposes an audio endpoint. The last exposed endpoint overrides all previous settings.

The Windows 7 Media Class Installer ignores this directive when it installs audio drivers. Therefore, when an audio driver is installed on Windows 7, the endpoints on the device do not necessarily become the default audio endpoint as they did on Windows Vista. You should update your Windows 7 audio driver INF files accordingly.




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