Can C# SAPI speak SSML string?

Question

I implemented a TTS in my C# WPF project.

Previously, I use the TTS in System.Speech.Synthesis namespace to speak. The speaking content is in SSML format (Speech Synthesizer Markup Language, support customize the speaking rate, voice, emphasize) like following:

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xml:lang="en-US"><prosody rate="x-fast">hello world. This is a long sentence speaking very fast!</prosody></speak>

But unfortunately the System.Speech.Synthesis TTS has a memory leak problem, as I mentioned in question Memory leak in .Net Speech.Synthesizer?.

So I decide to use SAPI COM component. I can easily let SAPI to speak plain text content. But then I continue to try letting it speak SSML string, I failed. The code is like following:

//Initialize TTS instance

SpeechLib.SpVoiceClass tts = new SpeechLib.SpVoiceClass();

//Generate SSML string

string textToSpeak = "hello world speak Extra Fast.";
PromptBuilder pb = new PromptBuilder();
pb.StartStyle(new PromptStyle(PromptRate.ExtraFast));
pb.AppendText(textToSpeak);
pb.EndStyle();

ssmlString = pb.ToXml();    //ssmlString = @"<speak version=""1.0"" .... 

//Speak!

tts.Speak(ssmlString, SpeechLib.SpeechVoiceSpeakFlags.SVSFParseSsml);

The essential part of the code is

tts.Speak(ssmlString, SpeechLib.SpeechVoiceSpeakFlags.SVSFParseSsml);

Which uses the SpeechVoiceSpeakFlags enumerations to specify the TTS speaking behavior. I have tried several combinations of the flags, but none of them successfully speak out the SSML content.

Particularly, the above code will also raise following exceptions:

System.Runtime.InteropServices.COMException was unhandled
Message="Exception from HRESULT: 0x80045003"
Source="Interop.SpeechLib" ErrorCode=-2147201021 StackTrace: at SpeechLib.SpVoiceClass.Speak(String Text, SpeechVoiceSpeakFlags Flags) at SpeechSynthesisMemLeakTest.Program.Test2() in D:\Proj\TestSolutions\CSharp_Quick_Apps\SpeechSynthesisMemLeakTest\Program.cs:line 60 at SpeechSynthesisMemLeakTest.Program.Main(String[] args) in D:\Proj\TestSolutions\CSharp_Quick_Apps\SpeechSynthesisMemLeakTest\Program.cs:line 17 at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException:

Could anyone tell me how to correctly use the flag to speak out SSML content?

Answer 1

What TTS engine/voice are you using? The Microsoft TTS engines definitely support SSML using the code that you're using; however, other voices/engines may not support SSML.

Error 0x80045003 is SPERR_UNSUPPORTED_FORMAT (The caller has specified an unsupported format), which leads me to believe that you need to use a different TTS engine (that supports SSML).

Answer 2

Use this flag instead

tts.Speak(ssmlString, SpeechLib.SpeechVoiceSpeakFlags.SVSFIsXML);

Tested using

• SpeechLib 5.4
• C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework.NETFramework\v4.5\System.Speech.dll