src/add-ons/media/media-add-ons/multi_audio/TimeComputer.cpp

   1 /*
   2  * Copyright 2009, Ingo Weinhold, ingo_weinhold@gmx.de.
   3  * Distributed under the terms of the MIT License.
   4  */
   5
   6
   7 #include "TimeComputer.h"
   8
   9
  10 TimeComputer::TimeComputer()
  11         :
  12         fRealTime(0),
  13         fPerformanceTime(0),
  14         fDrift(1),
  15         fFrameRate(1000000),
  16         fUsecsPerFrame(1),
  17         fPerformanceTimeBase(0),
  18         fFrameBase(0),
  19         fResetTimeBase(true),
  20         fFirstEntry(0),
  21         fLastEntry(0)
  22 {
  23 }
  24
  25
  26 void
  27 TimeComputer::Init(float frameRate, bigtime_t realBaseTime)
  28 {
  29         fRealTime = realBaseTime;
  30         fPerformanceTime = 0;
  31         fDrift = 1;
  32         SetFrameRate(frameRate);
  33 }
  34
  35
  36 void
  37 TimeComputer::SetFrameRate(float frameRate)
  38 {
  39         if (frameRate == fFrameRate)
  40                 return;
  41
  42         fFrameRate = frameRate;
  43         fUsecsPerFrame = (double)1000000 / fFrameRate;
  44         fResetTimeBase = true;
  45         fFirstEntry = 0;
  46         fLastEntry = 0;
  47 }
  48
  49
  50 void
  51 TimeComputer::AddTimeStamp(bigtime_t realTime, uint64 frames)
  52 {
  53         bigtime_t estimatedPerformanceTime = fPerformanceTime
  54                 + bigtime_t((realTime - fRealTime) * fDrift);
  55
  56         fRealTime = realTime;
  57
  58         if (fResetTimeBase) {
  59                 // use the extrapolated performance time at the given real time
  60                 fPerformanceTime = estimatedPerformanceTime;
  61                 fPerformanceTimeBase = estimatedPerformanceTime;
  62                 fFrameBase = frames;
  63                 fResetTimeBase = false;
  64                 _AddEntry(fRealTime, fPerformanceTime);
  65                 return;
  66         }
  67
  68         // add entry
  69         bigtime_t performanceTime = fPerformanceTimeBase
  70                 + bigtime_t((frames - fFrameBase) * fUsecsPerFrame);
  71         _AddEntry(realTime, performanceTime);
  72
  73         // Update performance time and drift. We don't use the given
  74         // performance time directly, but average it with the estimated
  75         // performance time.
  76         fPerformanceTime = (performanceTime + estimatedPerformanceTime) / 2;
  77
  78         Entry& entry = fEntries[fFirstEntry];
  79         fDrift = double(fPerformanceTime - entry.performanceTime)
  80                 / double(fRealTime - entry.realTime);
  81 }
  82
  83
  84 void
  85 TimeComputer::_AddEntry(bigtime_t realTime, bigtime_t performanceTime)
  86 {
  87         fLastEntry = (fLastEntry + 1) % kEntryCount;
  88         Entry& entry = fEntries[fLastEntry];
  89         entry.realTime = realTime;
  90         entry.performanceTime = performanceTime;
  91
  92         if (fLastEntry == fFirstEntry)
  93                 fFirstEntry = (fFirstEntry + 1) % kEntryCount;
  94 }