media/base/audio_hash.cc

   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
  14 namespace media {
  15
  16 AudioHash::AudioHash()
  17     : audio_hash_(),
  18       sample_count_(0) {
  19   COMPILE_ASSERT(arraysize(audio_hash_) == kHashBuckets, audio_hash_size_error);
  20 }
  21
  22 AudioHash::~AudioHash() {}
  23
  24 void AudioHash::Update(const AudioBus* audio_bus, int frames) {
  25   // Use uint32 to ensure overflow is a defined operation.
  26   for (uint32 ch = 0; ch < static_cast<uint32>(audio_bus->channels()); ++ch) {
  27     const float* channel = audio_bus->channel(ch);
  28     for (uint32 i = 0; i < static_cast<uint32>(frames); ++i) {
  29       const uint32 kSampleIndex = sample_count_ + i;
  30       const uint32 kHashIndex = (kSampleIndex * (ch + 1)) % kHashBuckets;
  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
  46 std::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