Replace Android system TTS engine (#508)

sherpa-onnx/csrc/offline-tts-impl.h

@@ -34,6 +34,10 @@ class OfflineTtsImpl {
 
   // Return the sample rate of the generated audio
   virtual int32_t SampleRate() const = 0;
+
+  // Number of supported speakers.
+  // If it supports only a single speaker, then it return 0 or 1.
+  virtual int32_t NumSpeakers() const = 0;
 };
 
 }  // namespace sherpa_onnx

sherpa-onnx/csrc/offline-tts-vits-impl.h

@@ -74,6 +74,10 @@ class OfflineTtsVitsImpl : public OfflineTtsImpl {
     return model_->GetMetaData().sample_rate;
   }
 
+  int32_t NumSpeakers() const override {
+    return model_->GetMetaData().num_speakers;
+  }
+
   GeneratedAudio Generate(
       const std::string &_text, int64_t sid = 0, float speed = 1.0,
       GeneratedAudioCallback callback = nullptr) const override {

sherpa-onnx/csrc/offline-tts.cc

@@ -73,4 +73,6 @@ GeneratedAudio OfflineTts::Generate(
 
 int32_t OfflineTts::SampleRate() const { return impl_->SampleRate(); }
 
+int32_t OfflineTts::NumSpeakers() const { return impl_->NumSpeakers(); }
+
 }  // namespace sherpa_onnx

sherpa-onnx/csrc/offline-tts.h

@@ -86,6 +86,10 @@ class OfflineTts {
   // Return the sample rate of the generated audio
   int32_t SampleRate() const;
 
+  // Number of supported speakers.
+  // If it supports only a single speaker, then it return 0 or 1.
+  int32_t NumSpeakers() const;
+
  private:
   std::unique_ptr<OfflineTtsImpl> impl_;
 };