Add a new UMA metric in APM to track incoming capture-side audio level

webrtc/modules/audio_processing/rms_level.cc

 /*
  *  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 "webrtc/modules/audio_processing/rms_level.h"
 
 #include <math.h>
 #include <algorithm>
 #include <numeric>
 
 #include "webrtc/base/checks.h"
 
 namespace webrtc {
 namespace {
 static constexpr float kMaxSquaredLevel = 32768 * 32768;
-static constexpr int kMinLevelDb = 127;
 // 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 kMinLevelDb;
+    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 * log10(mean_square_norm);
   RTC_DCHECK_LE(rms, 0.f);
-  RTC_DCHECK_GT(rms, -kMinLevelDb);
+  RTC_DCHECK_GT(rms, -RmsLevel::kMinLevelDb);
   // Return the negated value.
   return static_cast<int>(-rms + 0.5f);
 }
 }  // namespace
 
 RmsLevel::RmsLevel() {
   Reset();
 }
 
 RmsLevel::~RmsLevel() = default;
@@ skipping 21 matching lines @@
 
   max_sum_square_ = std::max(max_sum_square_, sum_square);
 }
 
 void RmsLevel::AnalyzeMuted(size_t length) {
   CheckBlockSize(length);
   sample_count_ += length;
 }
 
 int RmsLevel::Average() {
-  int rms = (sample_count_ == 0) ? kMinLevelDb
+  int rms = (sample_count_ == 0) ? RmsLevel::kMinLevelDb
                                  : ComputeRms(sum_square_ / sample_count_);
   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 rtc::Optional enforces this
   // with a DCHECK.
   Levels levels = (sample_count_ == 0)
-                      ? Levels{kMinLevelDb, kMinLevelDb}
+                      ? 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_ != rtc::Optional<size_t>(block_size)) {
     Reset();
     block_size_ = rtc::Optional<size_t>(block_size);
   }
 }
 }  // namespace webrtc