void
DurationIndex::AppendCTTSMode(REFERENCE_TIME tStart, REFERENCE_TIME tEnd)
{
// if the frames are out of order and the end time is invalid,
// we must use the frame rate to work out the difference
REFERENCE_TIME dur;
if (m_bUseFrameRate)
{
dur = m_tFrame;
}
else
{
dur = (tEnd - tStart);
}
// ToScale will round down, and this truncation causes the
// diff between decode and presentation time to get larger and larger
// so we sum both reference time and scaled totals and use the difference.
// That way the rounding error does not build up.
// the simpler version of these two lines is: cThis = long(ToScale(tEnd - tStart));
m_refDuration += dur;
long cThis = long(ToScale(m_refDuration) - m_TotalDuration);
// difference between sum of durations to here and actual CTS
// -- note: do this before adding current sample to total duration
long cDiff = long(ToScale(tStart) - m_TotalDuration);
AddDuration(cThis);
m_CTTS.Append(cDiff);
}
HRESULT
DurationIndex::WriteTable(Atom* patm)
{
// do nothing if no samples at all
HRESULT hr = S_OK;
if (m_nSamples <= mode_decide_count)
{
ModeDecide();
}
if (m_nSamples > 0)
{
if (!m_bCTTS)
{
// the final sample duration has not been recorded -- use the
// stop time
if (ToScale(m_tStopLast) > m_TotalDuration)
{
AddDuration(long(ToScale(m_tStopLast) - m_TotalDuration));
} else
// NOTE: We still need some duration recorded, to avoid stts/stsz discrepancy at the very least
AddDuration(1);
}
// create atom and write table
smart_ptr<Atom> pstts = patm->CreateAtom('stts');
m_STTS.Write(pstts);
pstts->Close();
if (m_bCTTS)
{
// write CTTS table
smart_ptr<Atom> pctts = patm->CreateAtom('ctts');
m_CTTS.Write(pctts);
pctts->Close();
}
}
return hr;
}
void
DurationIndex::Add(REFERENCE_TIME tStart, REFERENCE_TIME tEnd)
{
// In general it is safer to just use the start time of each sample
// since the stop time will be either wrong, or will just be deduced from
// the next sample start time.
// However, when frame re-ordering is happening, the composition time (== PTS) will
// not be the same as the decode time (== DTS) and we need to use both start and
// stop time to build the CTTS table.
// We save the first few timestamps and then decide which mode to be in.
if (m_nSamples < mode_decide_count)
{
if (m_nSamples == 0)
{
m_SumDurations = 0;
}
m_SumDurations += (tEnd - tStart);
m_SampleStarts[m_nSamples] = tStart;
m_SampleStops[m_nSamples] = tEnd;
m_nSamples++;
return;
}
else if (m_nSamples == mode_decide_count)
{
// this decides on a mode and then processes
// all the samples in the table
ModeDecide();
}
if (m_bCTTS)
{
AppendCTTSMode(tStart, tEnd);
}
else
{
AddDuration(long(ToScale(tStart) - m_TotalDuration));
}
m_nSamples++;
m_tStartLast = tStart;
m_tStopLast = tEnd;
return;
}
void
DurationIndex::ModeDecide()
{
if (m_nSamples > 0)
{
bool bReverse = false;
bool bDurOk = true;
LONGLONG ave = m_SumDurations / m_nSamples;
// 70fps is the maximum reasonable frame rate, so anything less than this is
// likely to be an error
const REFERENCE_TIME min_frame_dur = (UNITS / 70);
if (ave < min_frame_dur)
{
bDurOk = false;
}
// in the most common case, when converting from TS output, we don't
// get either accurate end times or an accuration rate in the media type.
// The smallest positive interval between frames should be the frame duration.
REFERENCE_TIME tInterval = 0;
for (int i = 0; i < m_nSamples; i++)
{
if (i > 0)
{
if (m_SampleStarts[i] < m_SampleStarts[i-1])
{
bReverse = true;
}
else
{
REFERENCE_TIME tThis = m_SampleStarts[i] - m_SampleStarts[i-1];
if (tThis > min_frame_dur)
{
if ((tInterval == 0) || (tThis < tInterval))
{
tInterval = tThis;
}
}
}
}
}
m_tStartFirst = m_SampleStarts[0];
// this interval is a better guess than the media type frame rate
if (tInterval > min_frame_dur)
{
m_tFrame = tInterval;
}
if (bReverse)
{
m_bCTTS = true;
if (!bDurOk)
{
m_bUseFrameRate = true;
}
else
{
m_bUseFrameRate = false;
}
// remember that the first frame might not be zero
m_TotalDuration = ToScale(m_tStartFirst);
m_refDuration = m_tStartFirst;
for (int i = 0; i < m_nSamples; i++)
{
AppendCTTSMode(m_SampleStarts[i], m_SampleStops[i]);
}
}
else
{
m_bCTTS = false;
m_TotalDuration = ToScale(m_tStartFirst);
for (int i = 1; i < m_nSamples; i++)
{
AddDuration(long(ToScale(m_SampleStarts[i]) - m_TotalDuration));
}
}
}
}
