media/cast/test/utility/audio_utility.h

   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 #ifndef MEDIA_CAST_TEST_UTILITY_AUDIO_UTILITY_H_
   6 #define MEDIA_CAST_TEST_UTILITY_AUDIO_UTILITY_H_
   7
   8 #include "media/audio/simple_sources.h"
   9
  10 namespace base {
  11 class TimeDelta;
  12 }
  13
  14 namespace media {
  15 class AudioBus;
  16 }
  17
  18 namespace media {
  19 namespace cast {
  20
  21 // Produces AudioBuses of varying duration where each successive output contains
  22 // the continuation of a single sine wave.
  23 class TestAudioBusFactory {
  24  public:
  25   TestAudioBusFactory(int num_channels,
  26                       int sample_rate,
  27                       float sine_wave_frequency,
  28                       float volume);
  29   ~TestAudioBusFactory();
  30
  31   // Creates a new AudioBus of the given |duration|, filled with the next batch
  32   // of sine wave samples.
  33   scoped_ptr<AudioBus> NextAudioBus(const base::TimeDelta& duration);
  34
  35   // A reasonable test tone.
  36   static const int kMiddleANoteFreq = 440;
  37
  38  private:
  39   const int num_channels_;
  40   const int sample_rate_;
  41   const float volume_;
  42   SineWaveAudioSource source_;
  43
  44   DISALLOW_COPY_AND_ASSIGN(TestAudioBusFactory);
  45 };
  46
  47 // Assuming |samples| contains a single-frequency sine wave (and maybe some
  48 // low-amplitude noise), count the number of times the sine wave crosses
  49 // zero.
  50 //
  51 // Example use case: When expecting a 440 Hz tone, this can be checked using the
  52 // following expression:
  53 //
  54 //   abs((CountZeroCrossings(...) / seconds_per_frame / 2) - 440) <= 1
  55 //
  56 // ...where seconds_per_frame is the number of samples divided by the sampling
  57 // rate.  The divide by two accounts for the fact that a sine wave crosses zero
  58 // twice per cycle (first downwards, then upwards).  The absolute maximum
  59 // difference of 1 accounts for the sine wave being out of perfect phase.
  60 int CountZeroCrossings(const float* samples, int length);
  61
  62 // Encode |timestamp| into the samples pointed to by 'samples' in a way
  63 // that should be decodable even after compressing/decompressing the audio.
  64 // Assumes 48Khz sampling rate and needs at least 240 samples. Returns
  65 // false if |length| of |samples| is too small. If more than 240 samples are
  66 // available, then the timestamp will be repeated. |sample_offset| should
  67 // contain how many samples has been encoded so far, so that we can make smooth
  68 // transitions between encoded chunks.
  69 // See audio_utility.cc for details on how the encoding is done.
  70 bool EncodeTimestamp(uint16 timestamp,
  71                      size_t sample_offset,
  72                      size_t length,
  73                      float* samples);
  74
  75 // Decode a timestamp encoded with EncodeTimestamp. Returns true if a
  76 // timestamp was found in |samples|.
  77 bool DecodeTimestamp(const float* samples, size_t length, uint16* timestamp);
  78
  79 }  // namespace cast
  80 }  // namespace media
  81
  82 #endif  // MEDIA_CAST_TEST_UTILITY_AUDIO_UTILITY_H_