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- // 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 MEDIA_BASE_AUDIO_HASH_H_
- #define MEDIA_BASE_AUDIO_HASH_H_
- #include <stddef.h>
- #include <stdint.h>
- #include <string>
- #include "base/strings/string_piece.h"
- #include "media/base/media_export.h"
- 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(const AudioHash&) = delete;
- AudioHash& operator=(const AudioHash&) = delete;
- ~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_;
- };
- } // namespace media
- #endif // MEDIA_BASE_AUDIO_HASH_H_
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