TTS to Stream with SpeechAudioFormatInfo using SpeechSynthesizer

Question

I am using System.Speech.Synthesis.SpeechSynthesizer to convert text to speech. And due to Microsoft\'s anemic documentation (see my link, there\'s no remarks or code exampl

Answer 1

Your code snippet is borked, you're using synth after it is disposed. But that's not the real problem I'm sure. SetOutputToAudioStream produces the raw PCM audio, the 'numbers'. Without a container file format (headers) like what's used in a .wav file. Yes, that cannot be played back with a regular media program.

The missing overload for SetOutputToWaveStream that takes a SpeechAudioFormatInfo is strange. It really does look like an oversight to me, even though that's extremely rare in the .NET framework. There's no compelling reason why it shouldn't work, the underlying SAPI interface does support it. It can be hacked around with reflection to call the private SetOutputStream method. This worked fine when I tested it but I can't vouch for it:

using System.Reflection;
...
            using (Stream ret = new MemoryStream())
            using (SpeechSynthesizer synth = new SpeechSynthesizer()) {
                var mi = synth.GetType().GetMethod("SetOutputStream", BindingFlags.Instance | BindingFlags.NonPublic);
                var fmt = new SpeechAudioFormatInfo(8000, AudioBitsPerSample.Eight, AudioChannel.Mono);
                mi.Invoke(synth, new object[] { ret, fmt, true, true });
                synth.Speak("Greetings from stack overflow");
                // Testing code:
                using (var fs = new FileStream(@"c:\temp\test.wav", FileMode.Create, FileAccess.Write, FileShare.None)) {
                    ret.Position = 0;
                    byte[] buffer = new byte[4096];
                    for (;;) {
                        int len = ret.Read(buffer, 0, buffer.Length);
                        if (len == 0) break;
                        fs.Write(buffer, 0, len);
                    }
                }
            }

If you're uncomfortable with the hack then using Path.GetTempFileName() to temporarily stream it to a file will certainly work.