Add online stream. (#28)

sherpa-onnx/csrc/online-stream.h

@@ -0,0 +1,73 @@
+// sherpa-onnx/csrc/online-stream.h
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#ifndef SHERPA_ONNX_CSRC_ONLINE_STREAM_H_
+#define SHERPA_ONNX_CSRC_ONLINE_STREAM_H_
+
+#include <memory>
+#include <vector>
+
+#include "sherpa-onnx/csrc/features.h"
+#include "sherpa-onnx/csrc/online-transducer-decoder.h"
+
+namespace sherpa_onnx {
+
+class OnlineStream {
+ public:
+  explicit OnlineStream(const FeatureExtractorConfig &config = {});
+  ~OnlineStream();
+
+  /**
+     @param sampling_rate The sampling_rate of the input waveform. Should match
+                          the one expected by the feature extractor.
+     @param waveform Pointer to a 1-D array of size n
+     @param n Number of entries in waveform
+   */
+  void AcceptWaveform(float sampling_rate, const float *waveform, int32_t n);
+
+  /**
+   * InputFinished() tells the class you won't be providing any
+   * more waveform.  This will help flush out the last frame or two
+   * of features, in the case where snip-edges == false; it also
+   * affects the return value of IsLastFrame().
+   */
+  void InputFinished();
+
+  int32_t NumFramesReady() const;
+
+  /** Note: IsLastFrame() will only ever return true if you have called
+   * InputFinished() (and this frame is the last frame).
+   */
+  bool IsLastFrame(int32_t frame) const;
+
+  /** Get n frames starting from the given frame index.
+   *
+   * @param frame_index  The starting frame index
+   * @param n  Number of frames to get.
+   * @return Return a 2-D tensor of shape (n, feature_dim).
+   *         which is flattened into a 1-D vector (flattened in in row major)
+   */
+  std::vector<float> GetFrames(int32_t frame_index, int32_t n) const;
+
+  void Reset();
+
+  int32_t FeatureDim() const;
+
+  // Return a reference to the number of processed frames so far.
+  // Initially, it is 0. It is always less than NumFramesReady().
+  //
+  // The returned reference is valid as long as this object is alive.
+  int32_t &GetNumProcessedFrames();
+
+  void SetResult(const OnlineTransducerDecoderResult &r);
+  const OnlineTransducerDecoderResult &GetResult() const;
+
+ private:
+  class Impl;
+  std::unique_ptr<Impl> impl_;
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_ONLINE_STREAM_H_