Did a quick check, MC's control point is using RelTime:
mapArguments.SetPropertyInt(_T("InstanceID"), 0);
bResult = Control(DLNA_SERVICE_AVTRANSPORT, AVTRANSPORT_FUNCTION_GET_POSITION_INFO, strStatus, &mapArguments, 6000, true);
if (!bResult || (mapArguments.GetProperty(_T("RelTime")).IsEqual(_T("NOT_IMPLEMENTED"))))
{
CLogHelper::Log(LOG_TYPE_PLAYBACK, _T("CDLNADeviceControl::GetPosition"), _T("GetPosition returned NOT_IMPLEMENTED for RelTime"));
bResult = false; // still need to set false if the call succeeded but returned NOT_IMPLEMENTED
}
}
// parse
if (bResult)
{
nPositionMS = JRMath::DTOI(JRDateTime::UnformatDurationHoursColonSecondsHighPrecision(mapArguments.GetProperty(_T("RelTime"))) * MILLISECONDS_IN_SECOND);
nDurationMS = JRMath::DTOI(JRDateTime::UnformatDurationHoursColonSecondsHighPrecision(mapArguments.GetProperty(_T("TrackDuration"))) * MILLISECONDS_IN_SECOND);
strTrackURI = mapArguments.GetProperty(_T("TrackURI"));
strTrackMetaData = mapArguments.GetProperty(_T("TrackMetaData"));
}