| // Copyright 2013 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef COBALT_MEDIA_BASE_AUDIO_HASH_H_ |
| #define COBALT_MEDIA_BASE_AUDIO_HASH_H_ |
| |
| #include <string> |
| |
| #include "base/basictypes.h" |
| #include "base/string_piece.h" |
| #include "cobalt/media/base/media_export.h" |
| #include "starboard/types.h" |
| |
| namespace cobalt { |
| namespace media { |
| |
| class AudioBus; |
| |
| // Computes a running hash for a series of AudioBus objects. The hash is the |
| // sum of each sample bucketed based on the frame index, channel number, and |
| // current hash count. The hash was designed with two properties in mind: |
| // |
| // 1. Uniform error distribution across the input sample. |
| // 2. Resilience to error below a certain threshold. |
| // |
| // The first is achieved by using a simple summing approach and moving position |
| // weighting into the bucket choice. The second is handled during conversion to |
| // string by rounding out values to only two decimal places. |
| // |
| // Using only two decimal places allows for roughly -40 dBFS of error. For |
| // reference, SincResampler produces an RMS error of around -15 dBFS. See |
| // http://en.wikipedia.org/wiki/DBFS and http://crbug.com/168204 for more info. |
| class MEDIA_EXPORT AudioHash { |
| public: |
| AudioHash(); |
| ~AudioHash(); |
| |
| // Update current hash with the contents of the provided AudioBus. |
| void Update(const AudioBus* audio_bus, int frames); |
| |
| // Return a string representation of the current hash. |
| std::string ToString() const; |
| |
| // Compare with another hash value given as string representation. |
| // Returns true if for every bucket the difference between this and |
| // other is less than tolerance. |
| bool IsEquivalent(const std::string& other, double tolerance) const; |
| |
| private: |
| // Storage for the audio hash. The number of buckets controls the importance |
| // of position in the hash. A higher number reduces the chance of false |
| // positives related to incorrect sample position. Value chosen by dice roll. |
| float audio_hash_[6]; |
| |
| // The total number of samples processed per channel. Uses a uint32_t instead |
| // of size_t so overflows on 64-bit and 32-bit machines are equivalent. |
| uint32_t sample_count_; |
| |
| DISALLOW_COPY_AND_ASSIGN(AudioHash); |
| }; |
| |
| } // namespace media |
| } // namespace cobalt |
| |
| #endif // COBALT_MEDIA_BASE_AUDIO_HASH_H_ |