Add microphone streaming ASR example for C API (#650)

c-api-examples/asr-microphone-example/CMakeLists.txt

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+
+add_executable(c-api-alsa c-api-alsa.cc alsa.cc)
+target_link_libraries(c-api-alsa sherpa-onnx-c-api cargs)
+
+if(DEFINED ENV{SHERPA_ONNX_ALSA_LIB_DIR})
+  target_link_libraries(c-api-alsa -L$ENV{SHERPA_ONNX_ALSA_LIB_DIR} -lasound)
+else()
+  target_link_libraries(c-api-alsa asound)
+endif()

c-api-examples/asr-microphone-example/CPPLINT.cfg

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+exclude_files=alsa.cc|alsa.h

c-api-examples/asr-microphone-example/README.md

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+# Introduction
+
+This folder contains examples for real-time speech recognition from a microphone
+using sherpa-onnx C API.
+
+**Note**: You can call C API from C++ files.
+
+
+## ./c-api-alsa.cc
+
+This file uses alsa to read a microphone. It runs only on Linux. This file
+does not support macOS or Windows.

c-api-examples/asr-microphone-example/alsa.cc

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+../../sherpa-onnx/csrc/alsa.cc

c-api-examples/asr-microphone-example/alsa.h

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+../../sherpa-onnx/csrc/alsa.h

c-api-examples/asr-microphone-example/c-api-alsa.cc

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+// c-api-examples/asr-microphone-example/c-api-alsa.cc
+// Copyright (c)  2022-2024  Xiaomi Corporation
+
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <algorithm>
+#include <cctype>  // std::tolower
+#include <cstdint>
+#include <string>
+
+#include "c-api-examples/asr-microphone-example/alsa.h"
+
+// NOTE: You don't need to use cargs.h in your own project.
+// We use it in this file to parse commandline arguments
+#include "cargs.h"  // NOLINT
+#include "sherpa-onnx/c-api/c-api.h"
+
+static struct cag_option options[] = {
+    {.identifier = 'h',
+     .access_letters = "h",
+     .access_name = "help",
+     .description = "Show help"},
+    {.identifier = 't',
+     .access_letters = NULL,
+     .access_name = "tokens",
+     .value_name = "tokens",
+     .description = "Tokens file"},
+    {.identifier = 'e',
+     .access_letters = NULL,
+     .access_name = "encoder",
+     .value_name = "encoder",
+     .description = "Encoder ONNX file"},
+    {.identifier = 'd',
+     .access_letters = NULL,
+     .access_name = "decoder",
+     .value_name = "decoder",
+     .description = "Decoder ONNX file"},
+    {.identifier = 'j',
+     .access_letters = NULL,
+     .access_name = "joiner",
+     .value_name = "joiner",
+     .description = "Joiner ONNX file"},
+    {.identifier = 'n',
+     .access_letters = NULL,
+     .access_name = "num-threads",
+     .value_name = "num-threads",
+     .description = "Number of threads"},
+    {.identifier = 'p',
+     .access_letters = NULL,
+     .access_name = "provider",
+     .value_name = "provider",
+     .description = "Provider: cpu (default), cuda, coreml"},
+    {.identifier = 'm',
+     .access_letters = NULL,
+     .access_name = "decoding-method",
+     .value_name = "decoding-method",
+     .description =
+         "Decoding method: greedy_search (default), modified_beam_search"},
+    {.identifier = 'f',
+     .access_letters = NULL,
+     .access_name = "hotwords-file",
+     .value_name = "hotwords-file",
+     .description = "The file containing hotwords, one words/phrases per line, "
+                    "and for each phrase the bpe/cjkchar are separated by a "
+                    "space. For example: ▁HE LL O ▁WORLD, 你 好 世 界"},
+    {.identifier = 's',
+     .access_letters = NULL,
+     .access_name = "hotwords-score",
+     .value_name = "hotwords-score",
+     .description = "The bonus score for each token in hotwords. Used only "
+                    "when decoding_method is modified_beam_search"},
+};
+
+const char *kUsage =
+    R"(
+Usage:
+  ./bin/c-api-alsa \
+    --tokens=/path/to/tokens.txt \
+    --encoder=/path/to/encoder.onnx \
+    --decoder=/path/to/decoder.onnx \
+    --joiner=/path/to/decoder.onnx \
+    device_name
+
+The device name specifies which microphone to use in case there are several
+on your system. You can use
+
+  arecord -l
+
+to find all available microphones on your computer. For instance, if it outputs
+
+**** List of CAPTURE Hardware Devices ****
+card 3: UACDemoV10 [UACDemoV1.0], device 0: USB Audio [USB Audio]
+  Subdevices: 1/1
+  Subdevice #0: subdevice #0
+
+and if you want to select card 3 and the device 0 on that card, please use:
+
+  plughw:3,0
+
+as the device_name.
+)";
+
+bool stop = false;
+
+static void Handler(int sig) {
+  stop = true;
+  fprintf(stderr, "\nCaught Ctrl + C. Exiting...\n");
+}
+
+int32_t main(int32_t argc, char *argv[]) {
+  if (argc < 6) {
+    fprintf(stderr, "%s\n", kUsage);
+    exit(0);
+  }
+
+  signal(SIGINT, Handler);
+
+  SherpaOnnxOnlineRecognizerConfig config;
+  memset(&config, 0, sizeof(config));
+
+  config.model_config.debug = 0;
+  config.model_config.num_threads = 1;
+  config.model_config.provider = "cpu";
+
+  config.decoding_method = "greedy_search";
+
+  config.max_active_paths = 4;
+
+  config.feat_config.sample_rate = 16000;
+  config.feat_config.feature_dim = 80;
+
+  config.enable_endpoint = 1;
+  config.rule1_min_trailing_silence = 2.4;
+  config.rule2_min_trailing_silence = 1.2;
+  config.rule3_min_utterance_length = 300;
+
+  cag_option_context context;
+  char identifier;
+  const char *value;
+
+  cag_option_prepare(&context, options, CAG_ARRAY_SIZE(options), argc, argv);
+
+  while (cag_option_fetch(&context)) {
+    identifier = cag_option_get(&context);
+    value = cag_option_get_value(&context);
+    switch (identifier) {
+      case 't':
+        config.model_config.tokens = value;
+        break;
+      case 'e':
+        config.model_config.transducer.encoder = value;
+        break;
+      case 'd':
+        config.model_config.transducer.decoder = value;
+        break;
+      case 'j':
+        config.model_config.transducer.joiner = value;
+        break;
+      case 'n':
+        config.model_config.num_threads = atoi(value);
+        break;
+      case 'p':
+        config.model_config.provider = value;
+        break;
+      case 'm':
+        config.decoding_method = value;
+        break;
+      case 'f':
+        config.hotwords_file = value;
+        break;
+      case 's':
+        config.hotwords_score = atof(value);
+        break;
+      case 'h': {
+        fprintf(stderr, "%s\n", kUsage);
+        exit(0);
+        break;
+      }
+      default:
+        // do nothing as config already has valid default values
+        break;
+    }
+  }
+
+  SherpaOnnxOnlineRecognizer *recognizer = CreateOnlineRecognizer(&config);
+  SherpaOnnxOnlineStream *stream = CreateOnlineStream(recognizer);
+
+  SherpaOnnxDisplay *display = CreateDisplay(50);
+  int32_t segment_id = 0;
+
+  const char *device_name = argv[context.index];
+  sherpa_onnx::Alsa alsa(device_name);
+  fprintf(stderr, "Use recording device: %s\n", device_name);
+  fprintf(stderr,
+          "Please \033[32m\033[1mspeak\033[0m! Press \033[31m\033[1mCtrl + "
+          "C\033[0m to exit\n");
+
+  int32_t expected_sample_rate = 16000;
+
+  if (alsa.GetExpectedSampleRate() != expected_sample_rate) {
+    fprintf(stderr, "sample rate: %d != %d\n", alsa.GetExpectedSampleRate(),
+            expected_sample_rate);
+    exit(-1);
+  }
+
+  int32_t chunk = 0.1 * alsa.GetActualSampleRate();
+
+  std::string last_text;
+
+  int32_t segment_index = 0;
+
+  while (!stop) {
+    const std::vector<float> &samples = alsa.Read(chunk);
+    AcceptWaveform(stream, expected_sample_rate, samples.data(),
+                   samples.size());
+    while (IsOnlineStreamReady(recognizer, stream)) {
+      DecodeOnlineStream(recognizer, stream);
+    }
+
+    const SherpaOnnxOnlineRecognizerResult *r =
+        GetOnlineStreamResult(recognizer, stream);
+
+    std::string text = r->text;
+    DestroyOnlineRecognizerResult(r);
+
+    if (!text.empty() && last_text != text) {
+      last_text = text;
+
+      std::transform(text.begin(), text.end(), text.begin(),
+                     [](auto c) { return std::tolower(c); });
+
+      SherpaOnnxPrint(display, segment_index, text.c_str());
+      fflush(stderr);
+    }
+
+    if (IsEndpoint(recognizer, stream)) {
+      if (!text.empty()) {
+        ++segment_index;
+      }
+      Reset(recognizer, stream);
+    }
+  }
+
+  // free allocated resources
+  DestroyDisplay(display);
+  DestroyOnlineStream(stream);
+  DestroyOnlineRecognizer(recognizer);
+  fprintf(stderr, "\n");
+
+  return 0;
+}