1 files changed, 65 insertions, 0 deletions
diff --git a/chromium/content/renderer/media/media_stream_audio_level_calculator.cc b/chromium/content/renderer/media/media_stream_audio_level_calculator.cc
new file mode 100644
index 00000000000..a136e32ae10
--- /dev/null
+++ b/chromium/content/renderer/media/media_stream_audio_level_calculator.cc
@@ -0,0 +1,65 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/renderer/media/media_stream_audio_level_calculator.h"
+
+#include "base/logging.h"
+#include "base/stl_util.h"
+
+namespace content {
+
+namespace {
+
+// Calculates the maximum absolute amplitude of the audio data.
+// Note, the return value can be bigger than std::numeric_limits<int16>::max().
+int MaxAmplitude(const int16* audio_data, int length) {
+  int max = 0, absolute = 0;
+  for (int i = 0; i < length; ++i) {
+    absolute = std::abs(audio_data[i]);
+    if (absolute > max)
+      max = absolute;
+  }
+  // The range of int16 is [-32768, 32767], verify the |max| should not be
+  // bigger than 32768.
+  DCHECK(max <= std::abs(std::numeric_limits<int16>::min()));
+
+  return max;
+}
+
+}  // namespace
+
+MediaStreamAudioLevelCalculator::MediaStreamAudioLevelCalculator()
+    : counter_(0),
+      max_amplitude_(0),
+      level_(0) {
+}
+
+MediaStreamAudioLevelCalculator::~MediaStreamAudioLevelCalculator() {
+}
+
+int MediaStreamAudioLevelCalculator::Calculate(const int16* audio_data,
+                                               int number_of_channels,
+                                               int number_of_frames) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  // |level_| is updated every 10 callbacks. For the case where callback comes
+  // every 10ms, |level_| will be updated approximately every 100ms.
+  static const int kUpdateFrequency = 10;
+
+  int max = MaxAmplitude(audio_data, number_of_channels * number_of_frames);
+  max_amplitude_ = std::max(max_amplitude_, max);
+
+  if (counter_++ == kUpdateFrequency) {
+    level_ = max_amplitude_;
+
+    // Decay the absolute maximum amplitude by 1/4.
+    max_amplitude_ >>= 2;
+
+    // Reset the counter.
+    counter_ = 0;
+  }
+
+  return level_;
+}
+
+}  // namespace content