Sxian/clt 2296/simple room plays welcome audio file (#10)

* Change SimpleRoom to play a welcome wav file rather than noise

* added git lfs to README

* removed a comment

Author: xianshijing-lk

.gitattributes

@@ -0,0 +1 @@
+data/welcome.wav filter=lfs diff=lfs merge=lfs -text

README.md

@@ -9,6 +9,9 @@ This SDK enables native C++ applications to connect to LiveKit servers for real-
 - **Rust / Cargo** (latest stable toolchain)  
 - **Protobuf** compiler (`protoc`)  
 - **macOS** users: System frameworks (CoreAudio, AudioToolbox, etc.) are automatically linked via CMake.
+- **Git LFS** (required for examples)
+  Some example data files (e.g., audio assets) are stored using Git LFS.
+  You must install Git LFS before cloning or pulling the repo if you want to run the examples.
 
 
 ## 🧩 Clone the Repository
@@ -51,7 +54,6 @@ export LIVEKIT_TOKEN=<jwt-token>
 
 Press Ctrl-C to exit the example.
 
-
 ##  🧰 Recommended Setup
 ### macOS
 ```bash

data/welcome.wav

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:e5a61a07be0392ac689876d33b92b75dc73442217188ff5d7ed23e7597d1ae98
+size 666724

examples/CMakeLists.txt

@@ -1,5 +1,16 @@
 cmake_minimum_required(VERSION 3.31.0)
 project (livekit-examples)
 
-add_executable(SimpleRoom simple_room/main.cpp)
+add_executable(SimpleRoom
+    simple_room/main.cpp
+    simple_room/wav_audio_source.cpp
+    simple_room/wav_audio_source.h
+)
+
 target_link_libraries(SimpleRoom livekit)
+
+add_custom_command(TARGET SimpleRoom POST_BUILD
+    COMMAND ${CMAKE_COMMAND} -E copy_directory
+            ${CMAKE_SOURCE_DIR}/data
+            ${CMAKE_CURRENT_BINARY_DIR}/data
+)

examples/simple_room/main.cpp

@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "livekit/livekit.h"
+#include "wav_audio_source.h"
 
 // TODO(shijing), remove this livekit_ffi.h as it should be internal only.
 #include "livekit_ffi.h"
@@ -129,19 +130,13 @@ void runNoiseCaptureLoop(const std::shared_ptr<AudioSource> &source) {
   const int frame_ms = 10;
   const int samples_per_channel = sample_rate * frame_ms / 1000;
 
-  std::mt19937 rng(std::random_device{}());
-  std::uniform_int_distribution<int16_t> noise_dist(-5000, 5000);
+  WavAudioSource WavAudioSource("data/welcome.wav", 48000, 1, false);
   using Clock = std::chrono::steady_clock;
   auto next_deadline = Clock::now();
   while (g_running.load(std::memory_order_relaxed)) {
     AudioFrame frame =
         AudioFrame::create(sample_rate, num_channels, samples_per_channel);
-    const std::size_t total_samples =
-        static_cast<std::size_t>(num_channels) *
-        static_cast<std::size_t>(samples_per_channel);
-    for (std::size_t i = 0; i < total_samples; ++i) {
-      frame.data()[i] = noise_dist(rng);
-    }
+    WavAudioSource.fillFrame(frame);
     try {
       source->captureFrame(frame);
     } catch (const std::exception &e) {

examples/simple_room/wav_audio_source.cpp

@@ -0,0 +1,162 @@
+/*
+ * Copyright 2025 LiveKit
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an “AS IS” BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "wav_audio_source.h"
+
+#include <cstring>
+#include <fstream>
+#include <stdexcept>
+
+// --------------------------------------------------
+// Minimal WAV loader (16-bit PCM only)
+// --------------------------------------------------
+WavData load_wav16(const std::string &path) {
+  std::ifstream file(path, std::ios::binary);
+  if (!file) {
+    throw std::runtime_error("Failed to open WAV file: " + path +
+                             " (If this file exists in the repo, ensure Git "
+                             "LFS is installed and run `git lfs pull`)");
+  }
+
+  auto read_u32 = [&](uint32_t &out_value) {
+    file.read(reinterpret_cast<char *>(&out_value), 4);
+  };
+  auto read_u16 = [&](uint16_t &out_value) {
+    file.read(reinterpret_cast<char *>(&out_value), 2);
+  };
+
+  char riff[4];
+  file.read(riff, 4);
+  if (std::strncmp(riff, "RIFF", 4) != 0) {
+    throw std::runtime_error("Not a RIFF file");
+  }
+
+  uint32_t chunk_size = 0;
+  read_u32(chunk_size);
+
+  char wave[4];
+  file.read(wave, 4);
+  if (std::strncmp(wave, "WAVE", 4) != 0) {
+    throw std::runtime_error("Not a WAVE file");
+  }
+
+  uint16_t audio_format = 0;
+  uint16_t num_channels = 0;
+  uint32_t sample_rate = 0;
+  uint16_t bits_per_sample = 0;
+
+  bool have_fmt = false;
+  bool have_data = false;
+  std::vector<int16_t> samples;
+
+  while (!have_data && file) {
+    char sub_id[4];
+    file.read(sub_id, 4);
+
+    uint32_t sub_size = 0;
+    read_u32(sub_size);
+
+    if (std::strncmp(sub_id, "fmt ", 4) == 0) {
+      have_fmt = true;
+
+      read_u16(audio_format);
+      read_u16(num_channels);
+      read_u32(sample_rate);
+
+      uint32_t byte_rate = 0;
+      uint16_t block_align = 0;
+      read_u32(byte_rate);
+      read_u16(block_align);
+      read_u16(bits_per_sample);
+
+      if (sub_size > 16) {
+        file.seekg(sub_size - 16, std::ios::cur);
+      }
+
+      if (audio_format != 1) {
+        throw std::runtime_error("Only PCM WAV supported");
+      }
+      if (bits_per_sample != 16) {
+        throw std::runtime_error("Only 16-bit WAV supported");
+      }
+
+    } else if (std::strncmp(sub_id, "data", 4) == 0) {
+      if (!have_fmt) {
+        throw std::runtime_error("data chunk appeared before fmt chunk");
+      }
+
+      have_data = true;
+      const std::size_t count = sub_size / sizeof(int16_t);
+      samples.resize(count);
+      file.read(reinterpret_cast<char *>(samples.data()), sub_size);
+
+    } else {
+      // Unknown chunk: skip it
+      file.seekg(sub_size, std::ios::cur);
+    }
+  }
+
+  if (!have_data) {
+    throw std::runtime_error("No data chunk in WAV file");
+  }
+
+  WavData out;
+  out.sample_rate = static_cast<int>(sample_rate);
+  out.num_channels = static_cast<int>(num_channels);
+  out.samples = std::move(samples);
+  return out;
+}
+
+WavAudioSource::WavAudioSource(const std::string &path,
+                               int expected_sample_rate, int expected_channels,
+                               bool loop_enabled)
+    : loop_enabled_(loop_enabled) {
+  wav_ = load_wav16(path);
+
+  if (wav_.sample_rate != expected_sample_rate) {
+    throw std::runtime_error("WAV sample rate mismatch");
+  }
+  if (wav_.num_channels != expected_channels) {
+    throw std::runtime_error("WAV channel count mismatch");
+  }
+
+  sample_rate_ = wav_.sample_rate;
+  num_channels_ = wav_.num_channels;
+
+  playhead_ = 0;
+}
+
+void WavAudioSource::fillFrame(AudioFrame &frame) {
+  const std::size_t frame_samples =
+      static_cast<std::size_t>(frame.num_channels()) *
+      static_cast<std::size_t>(frame.samples_per_channel());
+
+  int16_t *dst = frame.data().data();
+  const std::size_t total_wav_samples = wav_.samples.size();
+
+  for (std::size_t i = 0; i < frame_samples; ++i) {
+    if (playhead_ < total_wav_samples) {
+      dst[i] = wav_.samples[playhead_];
+      ++playhead_;
+    } else if (loop_enabled_ && total_wav_samples > 0) {
+      playhead_ = 0;
+      dst[i] = wav_.samples[playhead_];
+      ++playhead_;
+    } else {
+      dst[i] = 0;
+    }
+  }
+}

examples/simple_room/wav_audio_source.h

@@ -0,0 +1,56 @@
+
+/*
+ * Copyright 2025 LiveKit
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an “AS IS” BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include "livekit/livekit.h"
+#include <cstddef>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+// Simple WAV container for 16-bit PCM files
+struct WavData {
+  int sample_rate = 0;
+  int num_channels = 0;
+  std::vector<int16_t> samples;
+};
+
+// Helper that loads 16-bit PCM WAV (16-bit, PCM only)
+WavData loadWav16(const std::string &path);
+
+using namespace livekit;
+
+class WavAudioSource {
+public:
+  // loop_enabled: whether to loop when reaching the end
+  WavAudioSource(const std::string &path, int expected_sample_rate,
+                 int expected_channels, bool loop_enabled = true);
+
+  // Fill a frame with the next chunk of audio.
+  void fillFrame(AudioFrame &frame);
+
+private:
+  void initLoopDelayCounter();
+
+  WavData wav_;
+  std::size_t playhead_ = 0;
+
+  const bool loop_enabled_;
+  int sample_rate_;
+  int num_channels_;
+};