MF_PD_ASF_LANGLIST attribute
Specifies a list of language identifiers which specifies the languages contained in an Advanced Systems Format (ASF) file. This attribute corresponds to the Language List Object, defined in the ASF specification.
Data type
Byte array
Remarks
This attribute applies to presentation descriptors for ASF content.
The IMFASFContentInfo::GeneratePresentationDescriptor method creates the presentation descriptor and generates this attribute from the Language List Object header. The following table shows the format of the blob:
Language List Object field | Data type | Size | Description |
---|---|---|---|
Language ID Records Count | DWORD | 4 bytes | Number of languages |
Language ID Records | BYTE[] | Varies | Array of language strings (see below). |
The first DWORD is the number of languages, followed by an array of language identifier strings. Each string has the following format:
Language List Object field | Data type | Size | Description |
---|---|---|---|
Language ID Length | DWORD | 4 bytes | The length of the string in bytes, including the size of the trailing NULL character. |
Language ID | WCHAR[] | Varies | A null-terminated string containing the RFC 1766 language name. |
Each string is a language tag compliant with RFC 1766.
To get the language tag for a particular stream in the ASF file, query the stream descriptor for the MF_SD_ASF_EXTSTRMPROP_LANGUAGE_ID_INDEX attribute.
Examples
The following example shows how to parse the language list.
class LanguageList
{
private:
UINT8 *pRawList; // Unparsed blob
UINT32 cbList; // Size of the blob, in bytes
DWORD cLangs; // Number of languages
WCHAR **ppszLanguages; // Array of pointers to strings.
// These are pointers into pRawList.
public:
LanguageList() :
pRawList(NULL), cbList(0), ppszLanguages(NULL), cLangs(0)
{
}
~LanguageList()
{
Clear();
}
// Clear: Clears the list.
void Clear()
{
CoTaskMemFree(pRawList);
cbList = 0;
cLangs = 0;
delete [] ppszLanguages;
ppszLanguages = NULL;
}
// GetCount: Returns the number of languages.
DWORD GetCount() const { return cLangs; }
// GetLanguage: Return the i'th string in the list.
const WCHAR* GetLanguage(DWORD i)
{
if (i >= cLangs)
{
return NULL;
}
return ppszLanguages[i];
}
// Initialize: Get the language list, if specified, and parse it.
HRESULT Initialize(IMFPresentationDescriptor *pPD)
{
if (pPD == NULL)
{
return E_POINTER;
}
Clear();
HRESULT hr = pPD->GetAllocatedBlob(
MF_PD_ASF_LANGLIST, &pRawList, &cbList);
if (FAILED(hr))
{
goto done;
}
// Parse the language blob.
// Record count.
if (cbList < sizeof(DWORD))
{
hr = E_FAIL;
goto done;
}
cLangs = ((DWORD*)pRawList)[0];
// Allocate an array of pointers to language strings.
ppszLanguages = new (std::nothrow) WCHAR*[cLangs];
if (ppszLanguages == NULL)
{
hr = E_OUTOFMEMORY;
goto done;
}
ZeroMemory(ppszLanguages, cLangs * sizeof(WCHAR*));
BYTE *pNext = pRawList + sizeof(DWORD); // Next byte.
BYTE *pEnd = pRawList + cbList; // End of the blob.
for (DWORD i = 0; i < cLangs; i++)
{
if (pNext > pEnd - sizeof(DWORD))
{
hr = E_FAIL;
goto done;
}
// Language ID length
DWORD cbStr = ((DWORD*)pNext)[0];
pNext += sizeof(DWORD);
// Calculate the pointer to the language ID string.
if ((cbStr > (size_t)(pEnd - pNext)) ||
(cbStr < sizeof(WCHAR)) ||
(cbStr % sizeof(WCHAR) != 0))
{
hr = E_FAIL;
goto done;
}
ppszLanguages[i] = (WCHAR*)pNext;
// Verify the string is NULL-terminated.
if (ppszLanguages[i][(cbStr / sizeof(WCHAR)) - 1] != L'\0')
{
hr = E_FAIL;
goto done;
}
pNext += cbStr;
}
done:
if (FAILED(hr))
{
Clear();
}
if (hr == MF_E_ATTRIBUTENOTFOUND)
{
// There was no language list attribute in the PD.
// This is not a failure case.
hr = S_OK;
}
return hr;
}
private:
LanguageList(const LanguageList& lang);
LanguageList& operator=(const LanguageList& lang);
};
Requirements
Requirement | Value |
---|---|
Minimum supported client |
Windows Vista [desktop apps only] |
Minimum supported server |
Windows Server 2008 [desktop apps only] |
Header |
|
See also
-
ASF Header Object