How do I parse KLV data?

#1 Posted : Thursday, April 20, 2017 12:15:27 PM(UTC)

Walter

Groups: Tech Support
Posts: 366

Thanks: 1 times
Was thanked: 4 time(s) in 4 post(s)

The LEAD MPEG-2 Transport Demultiplexer supports parsing KLV as defined by SMPTE 336M-2001. Through the ILMMpgDmxCallback callback provided by the MPEG-2 TS demux, LEADTOOLS will provide any Universal, Local, or Minimum metadata found. It is up to the calling application to then look at the key and the the associated value.

In the LEADTOOLS SDK, the MPEG-2 Transport (player) demo illustrates how this is done. This demo specifically handles known KLV from Predator UAVs. Other KLV is ignored by the demo.

With the MPEG-2 Transport demo, the C++ code adding the callback looks like this:

Code:


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:

Code:


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 ;
}

The code recursively calls the EnumKlvKeys() method to handle decoding parent and child keys and uses the ILMKlvParser::GetKey() to get the data from they key.

Edited by moderator Wednesday, December 27, 2023 4:45:48 PM(UTC) | Reason: Updated

Walter Bates
Senior Support Engineer
LEAD Technologies, Inc.

Notification

How do I parse KLV data? - Parsing KLV


	Try the latest version of LEADTOOLS for free for 60 days by downloading the evaluation: https://www.leadtools.com/downloads Wanna join the discussion? Login to your LEADTOOLS Support account or Register a new forum account.