How do I parse KLV data? - c++

Question

How do I parse KLV data?
There is some codes below. I'd like to make a map using klv metadata. But how?
I know that the latitude and the longitude is in the 13th and 14th key in klv. But how could I use them and make a map.
ILMMpgDmx *CMainFrame::GetMPEG2DemuxInterface()
{
IUnknown *pSplitter;
HRESULT hr = m_player->GetSubObject(ltmmPlay_Object_Splitter, &pSplitter);
if (SUCCEEDED(hr))
{
ILMMpgDmx *pMpgDmx;
hr = pSplitter->QueryInterface(IID_ILMMpgDmx, (void **)&pMpgDmx);
if (SUCCEEDED(hr))
{
pSplitter->Release();
return pMpgDmx;
}
pSplitter->Release();
}
return NULL;
}
void CMainFrame::EnableMPEG2DemuxCallback()
{
HRESULT hr;
ILMMpgDmx *pMpgDmx = GetMPEG2DemuxInterface();
if (pMpgDmx)
{
// make sure the demux is not using the callback I am about to destroy
pMpgDmx->put_CallbackObj(NULL);
DeleteCallbackClass();
m_pCallback = new CMPEG2DemuxCallback(pMpgDmx);
// Force the callback to be called in the main thread. C++ applications in general can handle data in another thread, but our app is using MFC
// Our callback will display data in a window and MFC doesn't work well when you use windows from threads other than the main thread
// So, for simplicity, we will ask the demux to send the data to the main thread
hr = pMpgDmx->put_CallInSameThread(VARIANT_TRUE);
hr = pMpgDmx->put_CallbackObj(m_pCallback);
pMpgDmx->Release();
}
}
And the DataAvailable() function being called looks like this:
HRESULT STDMETHODCALLTYPE CMPEG2DemuxCallback::DataAvailable
(
/* [in] */ VARIANT *pData,
/* [in] */ long lDataSize,
/* [in] */ FileTypeConstants fileType,
/* [in] */ long streamPID,
/* [in] */ long streamType,
/* [in] */ PTSTypeConstants PTSType,
/* [in] */ double PTS,
/* [in] */ long flags
)
{
// skip small (most likely invalid) data chunks
if(lDataSize <= 1)
return S_OK;
//refresh control
{
static const DWORD MIN_REFRESH_TIME = 1000 ;//1 second
static DWORD dwLastTime = 0 ;//allow first data to be displayed
DWORD dwCurTime = GetTickCount ( ) ;
if ( dwCurTime - dwLastTime < MIN_REFRESH_TIME )
{
return S_OK ;
}
else
{
dwLastTime = dwCurTime ;
}
}
CPrivateDataView* pDataView = CPrivateDataViewManager::GetPrivateDataListView ( ) ;
if(!pDataView)
return S_OK;//skip
pDataView->SetRedraw ( FALSE ) ;
pDataView->GetListCtrl ( ).DeleteAllItems ( ) ;
{
HRESULT hr;
if(flags & DataFlag_IsKLV)
{
ILMKlvParser* pParser;
hr = m_pMpgDmx->GetKlvParser(streamPID, &pParser);
if(FAILED(hr))
return hr;
hr = EnumKlvKeys(pParser, pDataView, NULL, pData, lDataSize, flags);
if(FAILED(hr))
{
pParser->Release() ;
return hr;
}
pParser->Release();
}
else if(flags & DataFlag_IsAscii)
{
CString str;
hr = DumpVariantAsAscii(str, pData, lDataSize);
if(FAILED(hr))
return hr;
pDataView->AddValue (str) ;
}
else if(flags & DataFlag_IsBinary)
{
CString str;
hr = DumpVariantAsBinary(str, pData, lDataSize);
if(FAILED(hr))
return hr;
pDataView->AddValue (str) ;
}
else
{
ASSERT ( FALSE ) ;
return E_UNEXPECTED;
}
}
pDataView->SetRedraw ( TRUE ) ;
pDataView->RedrawWindow ( ) ;
return S_OK ;
}
These are all codes that I found. Also I found this klv library. I need a path for advicing.
https://github.com/Hunter522/libklv

Answer 1

I finally found how to parse KLV from MPEG2 TS.
i did the following
1. Use MPEg2- demux directshow filter that knows to parse the PID of metadata KLV.
2. i built my own directshow filter ( based on dump filter ) this filter accept in receive the entire PID of the KLV and than using the libklv from here
https://github.com/Hunter522/libklv
i added into the filter and this gave me the key , length and values.
But here is the trick:
KLV meta data can be part of protocol so in my case the protocol is MISB 601.8
here: https://upload.wikimedia.org/wikipedia/commons/1/19/MISB_Standard_0601.pdf
Every tag have its own formula, its units and name
there are 70 + tags.
thats mean that if a tag have 2 byte , go to its tag index in the MISB and the formula is there.