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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 #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_
     83