Add endpointing (#54)

sherpa-onnx/csrc/endpoint.h

@@ -0,0 +1,76 @@
+// sherpa-onnx/csrc/endpoint.h
+//
+// Copyright (c)  2022  (authors: Pingfeng Luo)
+//                2022-2023  Xiaomi Corporation
+
+#ifndef SHERPA_ONNX_CSRC_ENDPOINT_H_
+#define SHERPA_ONNX_CSRC_ENDPOINT_H_
+
+#include <string>
+#include <vector>
+
+namespace sherpa_onnx {
+
+struct EndpointRule {
+  // If True, for this endpointing rule to apply there must
+  // be nonsilence in the best-path traceback.
+  // For decoding, a non-blank token is considered as non-silence
+  bool must_contain_nonsilence = true;
+  // This endpointing rule requires duration of trailing silence
+  // (in seconds) to be >= this value.
+  float min_trailing_silence = 2.0;
+  // This endpointing rule requires utterance-length (in seconds)
+  // to be >= this value.
+  float min_utterance_length = 0.0f;
+
+  EndpointRule() = default;
+
+  EndpointRule(bool must_contain_nonsilence, float min_trailing_silence,
+               float min_utterance_length)
+      : must_contain_nonsilence(must_contain_nonsilence),
+        min_trailing_silence(min_trailing_silence),
+        min_utterance_length(min_utterance_length) {}
+
+  std::string ToString() const;
+};
+
+class ParseOptions;
+
+struct EndpointConfig {
+  // For default setting,
+  // rule1 times out after 2.4 seconds of silence, even if we decoded nothing.
+  // rule2 times out after 1.2 seconds of silence after decoding something.
+  // rule3 times out after the utterance is 20 seconds long, regardless of
+  // anything else.
+  EndpointRule rule1;
+  EndpointRule rule2;
+  EndpointRule rule3;
+
+  void Register(ParseOptions *po);
+
+  EndpointConfig()
+      : rule1{false, 2.4, 0}, rule2{true, 1.2, 0}, rule3{false, 0, 20} {}
+
+  EndpointConfig(const EndpointRule &rule1, const EndpointRule &rule2,
+                 const EndpointRule &rule3)
+      : rule1(rule1), rule2(rule2), rule3(rule3) {}
+
+  std::string ToString() const;
+};
+
+class Endpoint {
+ public:
+  explicit Endpoint(const EndpointConfig &config) : config_(config) {}
+
+  /// This function returns true if this set of endpointing rules thinks we
+  /// should terminate decoding.
+  bool IsEndpoint(int num_frames_decoded, int trailing_silence_frames,
+                  float frame_shift_in_seconds) const;
+
+ private:
+  EndpointConfig config_;
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_ENDPOINT_H_