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/*
* Copyright (c) 2016 The WebRTC Project Authors. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef WEBRTC_BASE_TIMESTAMPALIGNER_H_
#define WEBRTC_BASE_TIMESTAMPALIGNER_H_
#include <stdint.h>
#include "webrtc/base/constructormagic.h"
namespace rtc {
// The TimestampAligner class helps translating camera timestamps into
// the same timescale as is used by rtc::TimeMicros(). Some cameras
// have built in timestamping which is more accurate than reading the
// system clock, but using a different epoch and unknown clock drift.
// Frame timestamps in webrtc should use rtc::TimeMicros (system monotonic
// time), and this class provides a filter which lets us use the
// rtc::TimeMicros timescale, and at the same time take advantage of
// higher accuracy of the camera clock.
// This class is not thread safe, so all calls to it must be synchronized
// externally.
class TimestampAligner {
public:
TimestampAligner();
~TimestampAligner();
public:
// Translates camera timestamps to the same timescale as is used by
// rtc::TimeMicros(). |camera_time_us| is assumed to be accurate, but
// with an unknown epoch and clock drift. |system_time_us| is
// time according to rtc::TimeMicros(), preferably read as soon as
// possible when the frame is captured. It may have poor accuracy
// due to poor resolution or scheduling delays. Returns the
// translated timestamp.
int64_t TranslateTimestamp(int64_t camera_time_us, int64_t system_time_us);
protected:
// Update the estimated offset between camera time and system monotonic time.
int64_t UpdateOffset(int64_t camera_time_us, int64_t system_time_us);
// Clip timestamp, return value is always
// <= |system_time_us|, and
// >= min(|prev_translated_time_us_| + |kMinFrameIntervalUs|,
// |system_time_us|).
int64_t ClipTimestamp(int64_t filtered_time_us, int64_t system_time_us);
private:
// State for the timestamp translation.
int frames_seen_;
// Estimated offset between camera time and system monotonic time.
int64_t offset_us_;
// State for the ClipTimestamp method, applied after the filter.
// A large negative camera clock drift tends to push translated
// timestamps into the future. |clip_bias_us_| is subtracted from the
// translated timestamps, to get them back from the future.
int64_t clip_bias_us_;
// Used to ensure that translated timestamps are monotonous.
int64_t prev_translated_time_us_;
RTC_DISALLOW_COPY_AND_ASSIGN(TimestampAligner);
};
} // namespace rtc
#endif // WEBRTC_BASE_TIMESTAMPALIGNER_H_
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