Fix TTS for Unreal Engine (#2349)

Unreal Engine has its own memory management, so we cannot return a struct containing a std::vector object.

@@ -419,6 +419,19 @@ GeneratedAudio OfflineTts::Generate(const std::string &text,
   return ans;
 }
 
+std::shared_ptr<GeneratedAudio> OfflineTts::Generate2(
+    const std::string &text, int32_t sid /*= 0*/, float speed /*= 1.0*/,
+    OfflineTtsCallback callback /*= nullptr*/, void *arg /*= nullptr*/) const {
+  auto audio = Generate(text, sid, speed, callback, arg);
+
+  GeneratedAudio *ans = new GeneratedAudio;
+  ans->samples = std::move(audio.samples);
+  ans->sample_rate = audio.sample_rate;
+
+  return std::shared_ptr<GeneratedAudio>(ans,
+                                         [](GeneratedAudio *p) { delete p; });
+}
+
 KeywordSpotter KeywordSpotter::Create(const KeywordSpotterConfig &config) {
   struct SherpaOnnxKeywordSpotterConfig c;
   memset(&c, 0, sizeof(c));

@@ -6,6 +6,7 @@
 #ifndef SHERPA_ONNX_C_API_CXX_API_H_
 #define SHERPA_ONNX_C_API_CXX_API_H_
 
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -433,6 +434,13 @@ class SHERPA_ONNX_API OfflineTts
                           OfflineTtsCallback callback = nullptr,
                           void *arg = nullptr) const;
 
+  // Like Generate, but return a smart pointer.
+  //
+  // See also https://github.com/k2-fsa/sherpa-onnx/issues/2347
+  std::shared_ptr<GeneratedAudio> Generate2(
+      const std::string &text, int32_t sid = 0, float speed = 1.0,
+      OfflineTtsCallback callback = nullptr, void *arg = nullptr) const;
+
  private:
   explicit OfflineTts(const SherpaOnnxOfflineTts *p);
 };