Impostazione dei metadati in un file

Articolo
06/12/2023

È possibile impostare i metadati in un file prima di scriverlo nel dispositivo (quando si usa IWMDMStorageControl3::Insert3) o in un archivio esistente (chiamando IWMDMStorage3::SetMetadata). È possibile impostare gli attributi solo in un'archiviazione esistente chiamando IWMDMStorage::SetAttributes o IWMDMStorage2::SetAttributes2.

L'impostazione dei metadati viene eseguita creando e riempiendo un'interfaccia IWMDMMetaData passata a IWMDMStorageControl3::Insert3. Tuttavia, questo metodo può cancellare tutti i metadati esistenti nel file, diversi dai metadati hardcoded archiviati nel file system stesso, ad esempio nome file o dimensioni. Pertanto, è necessario copiare tutti i metadati esistenti che si desidera conservare nell'interfaccia IWMDMMetaData inviato. Poiché non è possibile usare Windows Media Gestione dispositivi per recuperare i metadati dai file locali, è necessario usare Windows Media Format SDK (o altri strumenti) per recuperare tali metadati.

Per usare Windows Media Format SDK per recuperare le proprietà dei file ASF, seguire questa procedura:

Creare un oggetto editor di metadati chiamando WMCreateEditor e richiedendo un'interfaccia IWMMetadataEditor .
Aprire il file per la lettura dei metadati chiamando IWMMetadataEditor::Open.
Se il file è un file ASF valido e può essere aperto, eseguire una query sull'editor per l'interfaccia IWMHeaderInfo .
Recuperare le proprietà del file chiamando IWMHeaderInfo::GetAttributeByName, passando la costante desiderata di Windows Media Format SDK. Nella tabella seguente viene fornito un elenco di costanti Format SDK con costanti Windows Media Gestione dispositivi SDK equivalenti.

Costante di Windows Media Format SDK	Costante di Windows Media Gestione dispositivi SDK
g_wszWMTitle	g_wszWMDMTitle
g_wszWMAuthor	g_wszWMDMAuthor
g_wszWMAlbumTitle	g_wszWMDMAlbumTitle
g_wszWMGenre	g_wszWMDMGenre
g_wszWMYear	g_wszWMDMYear
g_wszWMTrackNumber o g_wszWMTrack	g_wszWMDMTrack
g_wszWMComposer	g_wszWMDMComposer
g_wszWMDuration	g_wszWMDMDuration
g_wszWMCopyright	g_wszWMDMProviderCopyright
g_wszWMDescription	g_wszWMDMDescription
g_wszWMBitrate	g_wszWMDMBitrate
g_wszWMRating	g_wszWMDMUserRating
g_wszWMAlbumArtist	g_wszWMDMAlbumArtist
g_wszWMParentalRating	g_wszWMDMParentalRating
g_wszWMRadioStationName	g_wszWMDMMediaStationName
g_wszWMSubTitle	g_wszWMDMSubTitle
g_wszWMVideoWidth	g_wszWMDMWidth
g_wszWMVideoHeight	g_wszWMDMHeight
g_wszWMMood	g_wszWMDMTrackMood
g_wszWMCodec	g_wszAudioWAVECodec o g_wszVideoFourCCCodec

Il codice di esempio C++ seguente illustra il recupero di una serie di proprietà dei metadati da un file ASF usando Windows Media Format SDK e convertirli nei valori equivalenti di Windows Media Gestione dispositivi.

// Structure and array to hold equivalent Windows Media Format SDK 
// and Windows Media Device Manager SDK metadata property names.
struct EquivalentProperty
{
    LPCWSTR FormatSDKConst;
    LPCWSTR WMDMSDKConst;
};
EquivalentProperty EquivalentProperties []= 
{
    {g_wszWMTitle,        g_wszWMDMTitle},
    {g_wszWMAuthor,      g_wszWMDMAuthor},
    {g_wszWMAlbumTitle,  g_wszWMDMAlbumTitle},
    {g_wszWMGenre,       g_wszWMDMGenre},
    {g_wszWMYear,        g_wszWMDMYear},
    {g_wszWMTrackNumber, g_wszWMDMTrack},
    {g_wszWMTrack,       g_wszWMDMTrack},
    {g_wszWMComposer,    g_wszWMDMComposer},
    {g_wszWMBitrate,     g_wszWMDMBitrate},
    {g_wszWMDuration,    g_wszWMDMDuration},
    {g_wszWMCopyright,   g_wszWMDMProviderCopyright},
    {g_wszWMDescription, g_wszWMDMDescription},
    {g_wszWMRating,      g_wszWMDMUserRating},
    {g_wszWMAlbumArtist, g_wszWMDMAlbumArtist},
    {g_wszWMParentalRating,    g_wszWMDMParentalRating},
    {g_wszWMRadioStationName,  g_wszWMDMMediaStationName},
    {g_wszWMSubTitle,    g_wszWMDMSubTitle},
    {g_wszWMVideoWidth,  g_wszWMDMWidth},
    {g_wszWMVideoHeight, g_wszWMDMHeight},
    {g_wszWMMood,        g_wszWMDMTrackMood},
    {g_wszWMCodec,       g_wszAudioWAVECodec},
    {g_wszWMCodec,       g_wszVideoFourCCCodec}
};
// Function that tries to get metadata by using the Format SDK. 
// If it cannot open the file, it returns E_FAIL.
HRESULT GetFileMetadataFromFormatSDK(IWMDMMetaData* pMetadata, LPCWSTR file)
{
    if ((pMetaData == NULL) || (file == NULL)) return E_INVALIDPARAM;
    HRESULT hr = S_OK;
    CComPtr<IWMMetadataEditor> pEditor;

    // Do loop to allow easy error trapping. Even if there are no errors, 
    // the loop executes only once.
    do {
        hr = WMCreateEditor(&pEditor);
        if (FAILED(hr)) 
            break;

        // Open the file.
        hr = pEditor->Open(file);
        if (FAILED(hr)) 
            break;

        CComPtr<IWMHeaderInfo>pHeaderInfo;
        hr = pEditor->QueryInterface(__uuidof(IWMHeaderInfo), (void**)&pHeaderInfo);
        if (FAILED(hr))
            break;

        // Copy values from Format SDK to equivalent WMDM SDK metadata values.

        // Loop through all known values
        WORD stream = 0;
        WMT_ATTR_DATATYPE wmfType;
        WORD len = 0;
        BYTE* value = NULL;
        WMDM_TAG_DATATYPE wmdmType;
        for (int i = 0; i < sizeof(EquivalentProperties) / sizeof(EquivalentProperties[0]); i++)
        {
            // Request each value from our equivalency list by name.
            // The function is called twice: once to get the buffer size,
            // and once to get the value in the allocated buffer.
            if (FAILED(pHeaderInfo->GetAttributeByName(
                &stream, EquivalentProperties[i].FormatSDKConst, &wmfType, NULL, &len)))
            {
                continue;
            }

            value = new BYTE[len];
            if (value == NULL) continue;

            if (FAILED(pHeaderInfo->GetAttributeByName(&stream, EquivalentProperties[i].FormatSDKConst, &wmfType, value, &len)))
            {
                delete[] value;
                continue;
            }

            // Send the data to the equivalent WMDM metadata value.
            // First, find the equivalent WMDM type for the WMF type.
            switch(wmfType)
            {
            case WMT_TYPE_BINARY:
                wmdmType = WMDM_TYPE_BINARY;
                break;
            case WMT_TYPE_DWORD:
                wmdmType = WMDM_TYPE_DWORD;
                break;
            case WMT_TYPE_STRING:
                wmdmType = WMDM_TYPE_STRING;
                break;
            case WMT_TYPE_BOOL:
                wmdmType = WMDM_TYPE_BOOL;
                break;
            case WMT_TYPE_QWORD:
                wmdmType = WMDM_TYPE_QWORD;
                break;
            case WMT_TYPE_WORD:
                wmdmType = WMDM_TYPE_WORD;
                break;
            case WMT_TYPE_GUID:
                wmdmType = WMDM_TYPE_GUID;
                break;
            default:
                wmdmType = WMDM_TYPE_BINARY;
                break;
            }

            // Don't worry about trapping errors, because there's nothing 
            // we can do about it.
            pMetadata->AddItem(wmdmType, 
                EquivalentProperties[i].WMDMSDKConst, value, len);
            delete[] value;
        } // Add next value.
    } while (FALSE); // End Do loop error trap.

    // Close the file opened with IWMMetadataEditor.
    pEditor->Close();
    return hr;
}

La funzione di esempio C++ seguente illustra come usare DirectShow per ottenere alcune informazioni sui file e aggiungerla ai metadati.

// For IMediaDet, you must link to strmiids.lib. Also include the following:
//#include <Qedit.h>  // for IMediaDet declaration.
//#include <Dshow.h>  // for VIDEOINFOHEADER declaration.
HRESULT GetFileMetadataFromDShow(IWMDMMetaData* pMetadata, LPCWSTR file)
{
    HRESULT hr = S_OK;

    // Add file metadata properties from DirectShow. 
    // This is good for non-ASF files, or to add any information
    // that the Format SDK didn't get.

    // Do loop to allow easy error trapping. Even if there are no errors, 
    // the loop executes only once.
    do
    {
        // Create the Media Detector object.
        CComPtr<IMediaDet> pIMediaDet;
        hr = pIMediaDet.CoCreateInstance(CLSID_MediaDet, NULL);
        if (FAILED(hr)) 
            break;

        // Open the file.
        hr = pIMediaDet->put_Filename(BSTR(file));
        if (FAILED(hr))
            break;

        // Get the media type for the default stream.
        AM_MEDIA_TYPE mediaType;
        hr = pIMediaDet->get_StreamMediaType(&mediaType);
        if (FAILED(hr))
            break;

        // We have the file open, so start requesting information from the 
        // Media Detector and adding it to the metadata. When adding 
        // individual metadata values, ignore the HRESULT, because failure 
        // to add these metadata values is not a breaking issue.

        // Get major and minor types.
        WCHAR strMediaType[64];
        ZeroMemory(strMediaType, 64);

        //Change the major type to a string, then add to IWMDMMetaData.
        StringFromGUID2(reinterpret_cast<GUID&>(mediaType.majortype),
            (LPOLESTR)strMediaType, 64);
        hr = pMetadata->AddItem(WMDM_TYPE_STRING, 
             g_wszWMDMediaClassPrimaryID, 
            (BYTE*) strMediaType, 
             sizeof(strMediaType) / sizeof(strMediaType[0]));

        // Clear local string, then retrieve subtype the same way.
        ZeroMemory(strMediaType, 64);
        StringFromGUID2(reinterpret_cast<GUID&>(mediaType.subtype),
            (LPOLESTR)strMediaType, 64);
        hr = pMetadata->AddItem(WMDM_TYPE_STRING, 
            g_wszWMDMMediaClassSecondaryID, (BYTE*) strMediaType,
            sizeof(strMediaType) / sizeof(strMediaType[0]));

        // Get the duration. Duration is retrieved in seconds, but set 
        // in 100-nanosecond units.
        double duration = 0;
        hr = pIMediaDet->get_StreamLength(&duration);
        if (duration > 0)
        {
            duration *= 10E7;
            hr = pMetadata->AddItem(WMDM_TYPE_DWORD, g_wszWMDMDuration, (BYTE*) &duration, sizeof(duration));
        }

        // Get the frame rate.
        double frameRate = 0;
        hr = pIMediaDet->get_FrameRate(&frameRate);
        if (frameRate > 0)
        {
            hr = pMetadata->AddItem(WMDM_TYPE_DWORD, g_wszWMDMFrameRate, 
                (BYTE*) &frameRate,
                sizeof(frameRate));
        }

        // Get the structure for the default stream's major type and 
        // fill in additional information.

        if (IsEqualGUID(mediaType.formattype, FORMAT_VideoInfo))
        {
            VIDEOINFOHEADER* data = (VIDEOINFOHEADER*) mediaType.pbFormat;
            hr = pMetadata->AddItem(WMDM_TYPE_DWORD, g_wszWMDMVideoBitrate, 
               (BYTE*) &data->dwBitRate, sizeof(DWORD));
            hr = pMetadata->AddItem(WMDM_TYPE_DWORD, g_wszWMDMHeight, 
               (BYTE*) &data->bmiHeader.biHeight, sizeof(LONG));
            hr = pMetadata->AddItem(WMDM_TYPE_DWORD, g_wszWMDMWidth, 
               (BYTE*) &data->bmiHeader.biWidth, sizeof(LONG));
        }

        if (IsEqualGUID(mediaType.formattype, FORMAT_WaveFormatEx))
        {
            WAVEFORMATEX* data = (WAVEFORMATEX*) mediaType.pbFormat;
            hr = pMetadata->AddItem(WMDM_TYPE_WORD, g_wszWMDMBlockAlignment, 
                (BYTE*) &data->nBlockAlign, sizeof(WORD));
            hr = pMetadata->AddItem(WMDM_TYPE_WORD, g_wszWMDMNumChannels, 
               (BYTE*) &data->nChannels, sizeof(WORD));
        }
    } while (FALSE); // End of error loop.
    return hr;
}

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