How Tos

HOW: Retaining callback events for speech recognition and synthesis

The information in this article applies to:

• SpeechKit 6

Summary

Callback events are fired by audio devices, speech recognition, and synthesis engines to notify applications of processing states and to return data asynchronously.

The ChantAudio, ChantSR, and ChantTTS classes maintain event queues that enable applications to access event objects with event data.

More Information

Events are accessed from the event queue using the event object accessor methods such as GetResource, GetChantAudioEvent, GetChantSREvent, and GetChantTTSEvent depending on your programming language and environment.

The event queue is a read-only queue and only allows the application to access the oldest event on the queue. That event must be removed from the queue before the next event object may be accessed.

For some application scenarios, event data needs to be used asynchronously from when the event actually occurs. For example, in speech recognition, you may want to use event information to correct recognized speech. For speech synthesis, you may want to process the audio buffers through a device-specific handler.

To address these application scenarios, events can be persisted on a retention queue and accessed randomly via their identifier. To do this, applications use RetainResource rather than RemoveResource to remove the event from the queue. RetainResource removes the event object from the event queue and places it on a retention queue that the application can access and remove as needed.

A resource identifier (index token) is returned to the application on RetainResource. The application must maintain the identifier for accessing the event from the retention queue using the same event object accessor methods: GetResource, GetChantAudioEvent, GetChantSREvent, and GetChantTTSEvent. The difference is that the retained event identifier is passed with these methods to access a specific event object on the retention queue rather than the oldest event.

Once the event object is no longer needed, it may be destroyed and removed using the RemoveResource method with the retained event identifier.