Reland "Move webrtc/{base => rtc_base}" (https://codereview.webrtc.org/2877023002)
Reland the base->rtc_base without adding stub headers (will be
done in follow-up CL). This preserves git blame history of all files.
BUG=webrtc:7634
NOTRY=True
TBR=kwiberg@webrtc.org
Change-Id: Iea3bb6f3f67b8374c96337b63e8f5aa3e6181012
Reviewed-on: https://chromium-review.googlesource.com/554611
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18821}diff --git a/webrtc/rtc_base/timestampaligner.h b/webrtc/rtc_base/timestampaligner.h
new file mode 100644
index 0000000..90db4b9
--- /dev/null
+++ b/webrtc/rtc_base/timestampaligner.h
@@ -0,0 +1,74 @@
+/*
+ * 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_RTC_BASE_TIMESTAMPALIGNER_H_
+#define WEBRTC_RTC_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_RTC_BASE_TIMESTAMPALIGNER_H_