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
10namespace base {
11class TimeDelta;
12}
13
14namespace media {
15class AudioBus;
16}
17
18namespace media {
19namespace cast {
20
21// Produces AudioBuses of varying duration where each successive output contains
22// the continuation of a single sine wave.
23class 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.
60int 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.
70bool 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|.
77bool 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_
83