Index: content/renderer/media/media_stream_audio_level_calculator.cc |
diff --git a/content/renderer/media/media_stream_audio_level_calculator.cc b/content/renderer/media/media_stream_audio_level_calculator.cc |
new file mode 100644 |
index 0000000000000000000000000000000000000000..29b7faef1755c33ef9a26f01c36e7ff185b27e65 |
--- /dev/null |
+++ b/content/renderer/media/media_stream_audio_level_calculator.cc |
@@ -0,0 +1,82 @@ |
+// 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()); |
+ // Permutation of bars that reprents the amplitude level of the audio signal. |
ajm
2014/03/04 22:20:05
nit: represents
|
+ // The number of elements is 33 because we are indexing them in the range of |
+ // [0, 32]. |
+ static const int kPermutation[33] = |
+ {0,1,2,3,4,4,5,5,5,5,6,6,6,6,6,7,7,7,7,8,8,8,9,9,9,9,9,9,9,9,9,9,9}; |
+ |
+ // |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) { |
+ // Divide the max amplitude (32768) by 1000 to get in the range of [0,32] |
+ // which is the range of the permutation array. |
+ int index = static_cast<int>(max_amplitude_ / 1000); |
+ |
+ // Make it less likely that the bar stays at position 0. I.e. only if |
+ // its in the range 0-250 (instead of 0-1000) |
ajm
2014/03/04 22:20:05
nit: "i.e." "it's"
|
+ if (index == 0 && max_amplitude_ > 250) |
+ index = 1; |
+ |
+ // |level_| will be the value in the permutation array that the |index| is |
+ // pointing to. |
+ level_ = kPermutation[index]; |
+ |
+ // Decay the absolute maximum amplitude by 1/4. |
+ max_amplitude_ >>= 2; |
+ |
+ // Reset the counter. |
+ counter_ = 0; |
+ } |
+ |
+ return level_; |
+} |
+ |
+} // namespace content |