git-svn-id: http://webrtc.googlecode.com/svn/trunk@4 4adac7df-926f-26a2-2b94-8c16560cd09d

modules/video_coding/main/source/inter_frame_delay.cc

@@ -0,0 +1,120 @@
+/*
+ *  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 "inter_frame_delay.h"
+#include "tick_time.h"
+
+namespace webrtc {
+
+VCMInterFrameDelay::VCMInterFrameDelay()
+{
+    Reset();
+}
+
+// Resets the delay estimate
+void
+VCMInterFrameDelay::Reset()
+{
+    _zeroWallClock = VCMTickTime::MillisecondTimestamp();
+    _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(WebRtc_UWord32 timestamp,
+                                WebRtc_Word64 *delay,
+                                WebRtc_Word64 currentWallClock /* = -1 */)
+{
+    if (currentWallClock <= -1)
+    {
+        currentWallClock = VCMTickTime::MillisecondTimestamp();
+    }
+
+    if (_prevWallClock == 0)
+    {
+        // First set of data, initialization, wait for next frame
+        _prevWallClock = currentWallClock;
+        _prevTimestamp = timestamp;
+        *delay = 0;
+        return true;
+    }
+
+    WebRtc_Word32 prevWrapArounds = _wrapArounds;
+    CheckForWrapArounds(timestamp);
+
+    // This will be -1 for backward wrap arounds and +1 for forward wrap arounds
+    WebRtc_Word32 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<WebRtc_Word64>((timestamp + wrapAroundsSincePrev *
+                (static_cast<WebRtc_Word64>(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<WebRtc_Word64>(currentWallClock - _prevWallClock - _dTS);
+
+    _prevTimestamp = timestamp;
+    _prevWallClock = currentWallClock;
+
+    return true;
+}
+
+// Returns the current difference between incoming timestamps
+WebRtc_UWord32 VCMInterFrameDelay::CurrentTimeStampDiffMs() const
+{
+    if (_dTS < 0)
+    {
+        return 0;
+    }
+    return static_cast<WebRtc_UWord32>(_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(WebRtc_UWord32 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<WebRtc_Word32>(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<WebRtc_Word32>(_prevTimestamp - timestamp) > 0)
+    {
+        // Backward wrap around
+        _wrapArounds--;
+    }
+}
+
+}