audio_hash.cc revision 116680a4aac90f2aa7413d9095a592090648e557 
1// Copyright 2013 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// MSVC++ requires this to be set before any other includes to get M_PI.
6#define _USE_MATH_DEFINES
7#include <cmath>
8
9#include "media/base/audio_hash.h"
10
11#include "base/strings/stringprintf.h"
12#include "media/base/audio_bus.h"
13
14namespace media {
15
16AudioHash::AudioHash()
17    : audio_hash_(),
18      sample_count_(0) {
19}
20
21AudioHash::~AudioHash() {}
22
23void AudioHash::Update(const AudioBus* audio_bus, int frames) {
24  // Use uint32 to ensure overflow is a defined operation.
25  for (uint32 ch = 0; ch < static_cast<uint32>(audio_bus->channels()); ++ch) {
26    const float* channel = audio_bus->channel(ch);
27    for (uint32 i = 0; i < static_cast<uint32>(frames); ++i) {
28      const uint32 kSampleIndex = sample_count_ + i;
29      const uint32 kHashIndex =
30          (kSampleIndex * (ch + 1)) % arraysize(audio_hash_);
31
32      // Mix in a sine wave with the result so we ensure that sequences of empty
33      // buffers don't result in an empty hash.
34      if (ch == 0) {
35        audio_hash_[kHashIndex] +=
36            channel[i] + sin(2.0 * M_PI * M_PI * kSampleIndex);
37      } else {
38        audio_hash_[kHashIndex] += channel[i];
39      }
40    }
41  }
42
43  sample_count_ += static_cast<uint32>(frames);
44}
45
46std::string AudioHash::ToString() const {
47  std::string result;
48  for (size_t i = 0; i < arraysize(audio_hash_); ++i)
49    result += base::StringPrintf("%.2f,", audio_hash_[i]);
50  return result;
51}
52
53}  // namespace media
54