Fix Bug: Video with Variable Frame Rate plays at incorrect speed.

media/base/moving_average.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_BASE_MOVING_AVERAGE_H_
 #define MEDIA_BASE_MOVING_AVERAGE_H_
 
 #include <vector>
 
 #include "base/time/time.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 // Simple class for calculating a moving average of fixed size.
 class MEDIA_EXPORT MovingAverage {
  public:
   // Creates a MovingAverage instance with space for |depth| samples.
   explicit MovingAverage(size_t depth);
   ~MovingAverage();
 
   // Adds a new sample to the average; replaces the oldest sample if |depth_|
   // has been exceeded.  Updates |total_| to the new sum of values.
   void AddSample(base::TimeDelta sample);
 
   // Returns the current average of all held samples.
   base::TimeDelta Average() const;
 
+  // Returns the standard deviation of all held samples.
+  base::TimeDelta Deviation() const;
+
   // Resets the state of the class to its initial post-construction state.
   void Reset();
 
   size_t count() const { return count_; }
 
  private:
   // Maximum number of elements allowed in the average.
   const size_t depth_;
 
   // Number of elements seen thus far.
   uint64_t count_;
 
   std::vector<base::TimeDelta> samples_;
   base::TimeDelta total_;
+  double square_sum_ms_;

[DaleCurtis, 2015/11/20 23:50:46]

Store as base::TimeDelta

[qiangchen, 2015/11/25 18:06:33]

Probably may not be a good idea. 

As the unit is essentially second^2, not second.

And from programming perspective, there isn't multiplication and square root
defined for base::TimeDelta, and thus, even if we store the data in
base::TimeDelta, we will have to take out the raw value for computation.

 
   DISALLOW_COPY_AND_ASSIGN(MovingAverage);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_MOVING_AVERAGE_H_