TtsEngineAction Enumeration


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Specifies the Speech Synthesis Markup Language (SSML) action to be taken in rendering a given TextFragment.

Namespace:   System.Speech.Synthesis.TtsEngine
Assembly:  System.Speech (in System.Speech.dll)

public enum TtsEngineAction

Member nameDescription

Indicates that TextFragment is to be used as the contents of a bookmark.


Indicates that no action has been determined from SSML input.


Requests that input TextFragment text be interpreted as phonemes.


Indicates that a TextFragment contains no text to be rendered as speech.


Requests that the associated TextFragment should be processed and spoken.


Indicates that text values provided by a TextFragment through its TextToSpeak property are to be synthesize as individual characters.


Indicates state of paragraph.


Indicates start of sentence.

TtsEngineAction represents requests for servicing a TextFragment. The actions correspond closely to elements in the SSML specification and are implemented on the text returned by the TextToSpeak property on a TextFragment.

The TtsEngineAction value associated with a TextFragment is returned by the State property.

Processing of the TtsEngineAction value returned by the State property is handled by a speech synthesizes implementation of the Speak method on a class derived from TtsEngineSsml.

The example below is part of a custom speech synthesis implementation inheriting from TtsEngineSsml, and using the use of TextFragment, FragmentState, and TtsEventId

The implementation of Speak

  1. Receives an array of TextFragment instances and creates a new array of TextFragment instances to be passed to the Speak method on an underlying synthesis engine.

  2. If the TtsEngineAction enumeration value by found from the Action property on the FragmentState returned by the State property of each TextFragment instance is Speak, the implementation

    • Translates Americanism to Britishisms in the text to be spoken.

    • If the EventInterest property on the ITtsEngineSite interfaces provided to the implementation support the WordBoundary event type, an event to drive a synthesizer progress meter is created.

  3. A speech rendering engine is then called with the modified TextFragment array.

private const int WordBoundaryFlag = 1 << (int)TtsEventId.WordBoundary;
private readonly char[] spaces = new char[] { ' ', '\t', '\r', '\n' };
internal struct UsVsUk
  internal string UK;
  internal string US;

override public void Speak (TextFragment [] frags, IntPtr wfx, ITtsEngineSite site)
  TextFragment [] newFrags=new TextFragment[frags.Length];

  for (int i=0;i<frags.Length;i++){
    newFrags[i].TextToSpeak = frags[i].TextToSpeak.Substring(frags[i].TextOffset,
    newFrags[i].TextLength = newFrags[i].TextToSpeak.Length;
    newFrags[i].TextOffset = 0;
    if (newFrags[i].State.Action == TtsEngineAction.Speak) {
      //Us to UK conversion
      foreach (UsVsUk term in TransList) {
      newFrags[i].TextToSpeak.Replace(term.US, term.UK);
      //Generate progress meter events if supported
      if ((site.EventInterest & WordBoundaryFlag) != 0) {
      string[] subs = newFrags[i].TextToSpeak.Split(spaces);

      foreach (string s in subs) {
        int offset = newFrags[i].TextOffset;
        SpeechEventInfo spEvent = new SpeechEventInfo((Int16)TtsEventId.WordBoundary, 
                 s.Length, new IntPtr(offset));
        offset += s.Length;
        if (s.Trim().Length > 0) {
          SpeechEventInfo[] events = new SpeechEventInfo[1];
          events[0] = spEvent;
          site.AddEvents(events, 1);

  _baseSynthesize.Speak(newFrags, wfx, site);


.NET Framework
Available since 3.0
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