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35214fcfe2
Bug: webrtc:9419 Change-Id: I3225259fb4cc55e9820f590928795f4587f1e3cb Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/153884 Reviewed-by: Karl Wiberg <kwiberg@webrtc.org> Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org> Cr-Commit-Position: refs/heads/master@{#29479}
75 lines
2.9 KiB
C++
75 lines
2.9 KiB
C++
/*
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* Copyright (c) 2016 The WebRTC Project Authors. All rights reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef RTC_BASE_TIMESTAMP_ALIGNER_H_
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#define RTC_BASE_TIMESTAMP_ALIGNER_H_
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#include <stdint.h>
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#include "rtc_base/constructor_magic.h"
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#include "rtc_base/system/rtc_export.h"
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namespace rtc {
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// The TimestampAligner class helps translating camera timestamps into
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// the same timescale as is used by rtc::TimeMicros(). Some cameras
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// have built in timestamping which is more accurate than reading the
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// system clock, but using a different epoch and unknown clock drift.
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// Frame timestamps in webrtc should use rtc::TimeMicros (system monotonic
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// time), and this class provides a filter which lets us use the
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// rtc::TimeMicros timescale, and at the same time take advantage of
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// higher accuracy of the camera clock.
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// This class is not thread safe, so all calls to it must be synchronized
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// externally.
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class RTC_EXPORT TimestampAligner {
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public:
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TimestampAligner();
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~TimestampAligner();
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public:
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// Translates camera timestamps to the same timescale as is used by
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// rtc::TimeMicros(). |camera_time_us| is assumed to be accurate, but
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// with an unknown epoch and clock drift. |system_time_us| is
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// time according to rtc::TimeMicros(), preferably read as soon as
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// possible when the frame is captured. It may have poor accuracy
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// due to poor resolution or scheduling delays. Returns the
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// translated timestamp.
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int64_t TranslateTimestamp(int64_t camera_time_us, int64_t system_time_us);
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protected:
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// Update the estimated offset between camera time and system monotonic time.
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int64_t UpdateOffset(int64_t camera_time_us, int64_t system_time_us);
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// Clip timestamp, return value is always
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// <= |system_time_us|, and
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// >= min(|prev_translated_time_us_| + |kMinFrameIntervalUs|,
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// |system_time_us|).
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int64_t ClipTimestamp(int64_t filtered_time_us, int64_t system_time_us);
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private:
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// State for the timestamp translation.
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int frames_seen_;
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// Estimated offset between camera time and system monotonic time.
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int64_t offset_us_;
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// State for the ClipTimestamp method, applied after the filter.
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// A large negative camera clock drift tends to push translated
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// timestamps into the future. |clip_bias_us_| is subtracted from the
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// translated timestamps, to get them back from the future.
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int64_t clip_bias_us_;
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// Used to ensure that translated timestamps are monotonous.
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int64_t prev_translated_time_us_;
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RTC_DISALLOW_COPY_AND_ASSIGN(TimestampAligner);
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};
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} // namespace rtc
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#endif // RTC_BASE_TIMESTAMP_ALIGNER_H_
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