Implement timestamp translation/filter in VideoCapturer.

webrtc/base/timestampaligner.h

+/*
+ *  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 "webrtc/base/basictypes.h"
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/base/optional.h"
+
+namespace rtc {
+
+class TimestampAligner {
+ public:
+  TimestampAligner();
+  ~TimestampAligner();
+
+ public:
+  // Update the estimated offset between camera time and system monotonic time.
+  int64_t UpdateOffset(int64_t camera_time_us, int64_t 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 timestamp clipping, applied after the filter, to ensure
+  // that translated timestamps are monotonic and not in the future.
+  // Subtracted from the translated timestamps.
+  int64_t clip_bias_us_;
+  rtc::Optional<int64_t> prev_translated_time_us_;
+  RTC_DISALLOW_COPY_AND_ASSIGN(TimestampAligner);
+};
+
+}  // namespace rtc
+
+#endif  // WEBRTC_BASE_TIMESTAMPALIGNER_H_