1 files changed, 107 insertions, 0 deletions
diff --git a/webrtc/modules/video_coding/inter_frame_delay.cc b/webrtc/modules/video_coding/inter_frame_delay.cc
new file mode 100644
index 0000000000..fb3b54d204
--- /dev/null
+++ b/webrtc/modules/video_coding/inter_frame_delay.cc
@@ -0,0 +1,107 @@
+/*
+ *  Copyright (c) 2011 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.
+ */
+
+#include "webrtc/modules/video_coding/inter_frame_delay.h"
+
+namespace webrtc {
+
+VCMInterFrameDelay::VCMInterFrameDelay(int64_t currentWallClock) {
+  Reset(currentWallClock);
+}
+
+// Resets the delay estimate
+void VCMInterFrameDelay::Reset(int64_t currentWallClock) {
+  _zeroWallClock = currentWallClock;
+  _wrapArounds = 0;
+  _prevWallClock = 0;
+  _prevTimestamp = 0;
+  _dTS = 0;
+}
+
+// Calculates the delay of a frame with the given timestamp.
+// This method is called when the frame is complete.
+bool VCMInterFrameDelay::CalculateDelay(uint32_t timestamp,
+                                        int64_t* delay,
+                                        int64_t currentWallClock) {
+  if (_prevWallClock == 0) {
+    // First set of data, initialization, wait for next frame
+    _prevWallClock = currentWallClock;
+    _prevTimestamp = timestamp;
+    *delay = 0;
+    return true;
+  }
+
+  int32_t prevWrapArounds = _wrapArounds;
+  CheckForWrapArounds(timestamp);
+
+  // This will be -1 for backward wrap arounds and +1 for forward wrap arounds
+  int32_t wrapAroundsSincePrev = _wrapArounds - prevWrapArounds;
+
+  // Account for reordering in jitter variance estimate in the future?
+  // Note that this also captures incomplete frames which are grabbed
+  // for decoding after a later frame has been complete, i.e. real
+  // packet losses.
+  if ((wrapAroundsSincePrev == 0 && timestamp < _prevTimestamp) ||
+      wrapAroundsSincePrev < 0) {
+    *delay = 0;
+    return false;
+  }
+
+  // Compute the compensated timestamp difference and convert it to ms and
+  // round it to closest integer.
+  _dTS = static_cast<int64_t>(
+      (timestamp + wrapAroundsSincePrev * (static_cast<int64_t>(1) << 32) -
+       _prevTimestamp) /
+          90.0 +
+      0.5);
+
+  // frameDelay is the difference of dT and dTS -- i.e. the difference of
+  // the wall clock time difference and the timestamp difference between
+  // two following frames.
+  *delay = static_cast<int64_t>(currentWallClock - _prevWallClock - _dTS);
+
+  _prevTimestamp = timestamp;
+  _prevWallClock = currentWallClock;
+
+  return true;
+}
+
+// Returns the current difference between incoming timestamps
+uint32_t VCMInterFrameDelay::CurrentTimeStampDiffMs() const {
+  if (_dTS < 0) {
+    return 0;
+  }
+  return static_cast<uint32_t>(_dTS);
+}
+
+// Investigates if the timestamp clock has overflowed since the last timestamp
+// and
+// keeps track of the number of wrap arounds since reset.
+void VCMInterFrameDelay::CheckForWrapArounds(uint32_t timestamp) {
+  if (timestamp < _prevTimestamp) {
+    // This difference will probably be less than -2^31 if we have had a wrap
+    // around
+    // (e.g. timestamp = 1, _previousTimestamp = 2^32 - 1). Since it is cast to
+    // a Word32,
+    // it should be positive.
+    if (static_cast<int32_t>(timestamp - _prevTimestamp) > 0) {
+      // Forward wrap around
+      _wrapArounds++;
+    }
+    // This difference will probably be less than -2^31 if we have had a
+    // backward
+    // wrap around.
+    // Since it is cast to a Word32, it should be positive.
+  } else if (static_cast<int32_t>(_prevTimestamp - timestamp) > 0) {
+    // Backward wrap around
+    _wrapArounds--;
+  }
+}
+}  // namespace webrtc