1 files changed, 138 insertions, 0 deletions
diff --git a/third_party/libwebrtc/modules/audio_processing/rms_level.cc b/third_party/libwebrtc/modules/audio_processing/rms_level.cc
new file mode 100644
index 0000000000..b0a45cb403
--- /dev/null
+++ b/third_party/libwebrtc/modules/audio_processing/rms_level.cc
@@ -0,0 +1,138 @@
+/*
+ *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "modules/audio_processing/rms_level.h"
+
+#include <algorithm>
+#include <cmath>
+#include <numeric>
+
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+namespace {
+static constexpr float kMaxSquaredLevel = 32768 * 32768;
+// kMinLevel is the level corresponding to kMinLevelDb, that is 10^(-127/10).
+static constexpr float kMinLevel = 1.995262314968883e-13f;
+
+// Calculates the normalized RMS value from a mean square value. The input
+// should be the sum of squared samples divided by the number of samples. The
+// value will be normalized to full range before computing the RMS, wich is
+// returned as a negated dBfs. That is, 0 is full amplitude while 127 is very
+// faint.
+int ComputeRms(float mean_square) {
+  if (mean_square <= kMinLevel * kMaxSquaredLevel) {
+    // Very faint; simply return the minimum value.
+    return RmsLevel::kMinLevelDb;
+  }
+  // Normalize by the max level.
+  const float mean_square_norm = mean_square / kMaxSquaredLevel;
+  RTC_DCHECK_GT(mean_square_norm, kMinLevel);
+  // 20log_10(x^0.5) = 10log_10(x)
+  const float rms = 10.f * std::log10(mean_square_norm);
+  RTC_DCHECK_LE(rms, 0.f);
+  RTC_DCHECK_GT(rms, -RmsLevel::kMinLevelDb);
+  // Return the negated value.
+  return static_cast<int>(-rms + 0.5f);
+}
+}  // namespace
+
+RmsLevel::RmsLevel() {
+  Reset();
+}
+
+RmsLevel::~RmsLevel() = default;
+
+void RmsLevel::Reset() {
+  sum_square_ = 0.f;
+  sample_count_ = 0;
+  max_sum_square_ = 0.f;
+  block_size_ = absl::nullopt;
+}
+
+void RmsLevel::Analyze(rtc::ArrayView<const int16_t> data) {
+  if (data.empty()) {
+    return;
+  }
+
+  CheckBlockSize(data.size());
+
+  const float sum_square =
+      std::accumulate(data.begin(), data.end(), 0.f,
+                      [](float a, int16_t b) { return a + b * b; });
+  RTC_DCHECK_GE(sum_square, 0.f);
+  sum_square_ += sum_square;
+  sample_count_ += data.size();
+
+  max_sum_square_ = std::max(max_sum_square_, sum_square);
+}
+
+void RmsLevel::Analyze(rtc::ArrayView<const float> data) {
+  if (data.empty()) {
+    return;
+  }
+
+  CheckBlockSize(data.size());
+
+  float sum_square = 0.f;
+
+  for (float data_k : data) {
+    int16_t tmp =
+        static_cast<int16_t>(std::min(std::max(data_k, -32768.f), 32767.f));
+    sum_square += tmp * tmp;
+  }
+  RTC_DCHECK_GE(sum_square, 0.f);
+  sum_square_ += sum_square;
+  sample_count_ += data.size();
+
+  max_sum_square_ = std::max(max_sum_square_, sum_square);
+}
+
+void RmsLevel::AnalyzeMuted(size_t length) {
+  CheckBlockSize(length);
+  sample_count_ += length;
+}
+
+int RmsLevel::Average() {
+  const bool have_samples = (sample_count_ != 0);
+  int rms = have_samples ? ComputeRms(sum_square_ / sample_count_)
+                         : RmsLevel::kMinLevelDb;
+
+  // To ensure that kMinLevelDb represents digital silence (muted audio
+  // sources) we'll check here if the sum_square is actually 0. If it's not
+  // we'll bump up the return value to `kInaudibleButNotMuted`.
+  // https://datatracker.ietf.org/doc/html/rfc6464
+  if (have_samples && rms == RmsLevel::kMinLevelDb && sum_square_ != 0.0f) {
+    rms = kInaudibleButNotMuted;
+  }
+
+  Reset();
+  return rms;
+}
+
+RmsLevel::Levels RmsLevel::AverageAndPeak() {
+  // Note that block_size_ should by design always be non-empty when
+  // sample_count_ != 0. Also, the * operator of absl::optional enforces this
+  // with a DCHECK.
+  Levels levels = (sample_count_ == 0)
+                      ? Levels{RmsLevel::kMinLevelDb, RmsLevel::kMinLevelDb}
+                      : Levels{ComputeRms(sum_square_ / sample_count_),
+                               ComputeRms(max_sum_square_ / *block_size_)};
+  Reset();
+  return levels;
+}
+
+void RmsLevel::CheckBlockSize(size_t block_size) {
+  if (block_size_ != block_size) {
+    Reset();
+    block_size_ = block_size;
+  }
+}
+}  // namespace webrtc