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1 // Copyright 2014 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 #include "content/renderer/media/media_stream_audio_level_calculator.h" | |
6 | |
7 #include "base/logging.h" | |
8 #include "base/stl_util.h" | |
9 | |
10 namespace content { | |
11 | |
12 namespace { | |
13 | |
14 // Calculates the maximum absolute amplitude of the audio data. | |
15 // Note, the return value can be bigger than std::numeric_limits<int16>::max(). | |
16 int MaxAmplitude(const int16* audio_data, int length) { | |
17 int max = 0, absolute = 0; | |
18 for (int i = 0; i < length; ++i) { | |
19 absolute = std::abs(audio_data[i]); | |
20 if (absolute > max) | |
21 max = absolute; | |
22 } | |
23 // The range of int16 is [-32768, 32767], verify the |max| should not be | |
24 // bigger than 32768. | |
25 DCHECK(max <= std::abs(std::numeric_limits<int16>::min())); | |
26 | |
27 return max; | |
28 } | |
29 | |
30 } // namespace | |
31 | |
32 MediaStreamAudioLevelCalculator::MediaStreamAudioLevelCalculator() | |
33 : counter_(0), | |
34 max_amplitude_(0), | |
35 level_(0) { | |
36 } | |
37 | |
38 MediaStreamAudioLevelCalculator::~MediaStreamAudioLevelCalculator() { | |
39 } | |
40 | |
41 int MediaStreamAudioLevelCalculator::Calculate(const int16* audio_data, | |
42 int number_of_channels, | |
43 int number_of_frames) { | |
44 DCHECK(thread_checker_.CalledOnValidThread()); | |
45 // Permutation of bars that reprents the amplitude level of the audio signal. | |
ajm
2014/03/04 22:20:05
nit: represents
| |
46 // The number of elements is 33 because we are indexing them in the range of | |
47 // [0, 32]. | |
48 static const int kPermutation[33] = | |
49 {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}; | |
50 | |
51 // |level_| is updated every 10 callbacks. For the case where callback comes | |
52 // every 10ms, |level_| will be updated approximately every 100ms. | |
53 static const int kUpdateFrequency = 10; | |
54 | |
55 int max = MaxAmplitude(audio_data, number_of_channels * number_of_frames); | |
56 max_amplitude_ = std::max(max_amplitude_, max); | |
57 | |
58 if (counter_++ == kUpdateFrequency) { | |
59 // Divide the max amplitude (32768) by 1000 to get in the range of [0,32] | |
60 // which is the range of the permutation array. | |
61 int index = static_cast<int>(max_amplitude_ / 1000); | |
62 | |
63 // Make it less likely that the bar stays at position 0. I.e. only if | |
64 // its in the range 0-250 (instead of 0-1000) | |
ajm
2014/03/04 22:20:05
nit: "i.e." "it's"
| |
65 if (index == 0 && max_amplitude_ > 250) | |
66 index = 1; | |
67 | |
68 // |level_| will be the value in the permutation array that the |index| is | |
69 // pointing to. | |
70 level_ = kPermutation[index]; | |
71 | |
72 // Decay the absolute maximum amplitude by 1/4. | |
73 max_amplitude_ >>= 2; | |
74 | |
75 // Reset the counter. | |
76 counter_ = 0; | |
77 } | |
78 | |
79 return level_; | |
80 } | |
81 | |
82 } // namespace content | |
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