third_party/libwebrtc/modules/audio_processing/rms_level.h

   1 /*
   2  *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
   3  *
   4  *  Use of this source code is governed by a BSD-style license
   5  *  that can be found in the LICENSE file in the root of the source
   6  *  tree. An additional intellectual property rights grant can be found
   7  *  in the file PATENTS.  All contributing project authors may
   8  *  be found in the AUTHORS file in the root of the source tree.
   9  */
  10
  11 #ifndef MODULES_AUDIO_PROCESSING_RMS_LEVEL_H_
  12 #define MODULES_AUDIO_PROCESSING_RMS_LEVEL_H_
  13
  14 #include <stddef.h>
  15 #include <stdint.h>
  16
  17 #include "absl/types/optional.h"
  18 #include "api/array_view.h"
  19
  20 namespace webrtc {
  21
  22 // Computes the root mean square (RMS) level in dBFs (decibels from digital
  23 // full-scale) of audio data. The computation follows RFC 6465:
  24 // https://tools.ietf.org/html/rfc6465
  25 // with the intent that it can provide the RTP audio level indication.
  26 //
  27 // The expected approach is to provide constant-sized chunks of audio to
  28 // Analyze(). When enough chunks have been accumulated to form a packet, call
  29 // Average() to get the audio level indicator for the RTP header.
  30 class RmsLevel {
  31  public:
  32   struct Levels {
  33     int average;
  34     int peak;
  35   };
  36
  37   enum : int { kMinLevelDb = 127, kInaudibleButNotMuted = 126 };
  38
  39   RmsLevel();
  40   ~RmsLevel();
  41
  42   // Can be called to reset internal states, but is not required during normal
  43   // operation.
  44   void Reset();
  45
  46   // Pass each chunk of audio to Analyze() to accumulate the level.
  47   void Analyze(rtc::ArrayView<const int16_t> data);
  48   void Analyze(rtc::ArrayView<const float> data);
  49
  50   // If all samples with the given `length` have a magnitude of zero, this is
  51   // a shortcut to avoid some computation.
  52   void AnalyzeMuted(size_t length);
  53
  54   // Computes the RMS level over all data passed to Analyze() since the last
  55   // call to Average(). The returned value is positive but should be interpreted
  56   // as negative as per the RFC. It is constrained to [0, 127]. Resets the
  57   // internal state to start a new measurement period.
  58   int Average();
  59
  60   // Like Average() above, but also returns the RMS peak value. Resets the
  61   // internal state to start a new measurement period.
  62   Levels AverageAndPeak();
  63
  64  private:
  65   // Compares `block_size` with `block_size_`. If they are different, calls
  66   // Reset() and stores the new size.
  67   void CheckBlockSize(size_t block_size);
  68
  69   float sum_square_;
  70   size_t sample_count_;
  71   float max_sum_square_;
  72   absl::optional<size_t> block_size_;
  73 };
  74
  75 }  // namespace webrtc
  76
  77 #endif  // MODULES_AUDIO_PROCESSING_RMS_LEVEL_H_