Fix TTS for Unreal Engine (#2349)

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

sherpa-onnx/c-api/cxx-api.cc

@@ -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));