IWMHeaderInfo3::ModifyAttribute method

The ModifyAttribute method modifies the settings of an existing attribute.


HRESULT ModifyAttribute(
  [in]       WORD              wStreamNum,
  [in]       WORD              wIndex,
  [in]       WMT_ATTR_DATATYPE Type,
  [in]       WORD              wLangIndex,
  [inconst BYTE              *pValue,
  [in]       DWORD             dwLength


wStreamNum [in]

WORD containing the stream number to which the attribute applies. Pass zero for file-level attributes.

wIndex [in]

WORD containing the index of the attribute to change.

Type [in]

Type of data used for the new attribute value. For more information about the types of data supported, see WMT_ATTR_DATATYPE.

wLangIndex [in]

WORD containing the language index of the language to be associated with the new attribute. This is the index of the language in the language list for the file.

pValue [in]

Pointer to an array of bytes containing the attribute value.

dwLength [in]

DWORD containing the length of the attribute value, in bytes.

Return value

The method returns an HRESULT. Possible values include, but are not limited to, those in the following table.

Return codeDescription

The method succeeded.


An illegal parameter combination, data type, or attribute name was used.


The method is not implemented on a reader object.


A pointer is not valid.


The attribute cannot be changed.


wStreamNum is not a valid stream number, or there is no attribute at wIndex.



You can use 0xFFFF for the stream number to specify an attribute using its global index. Global index values range from 0 to one less than the count of attributes received from a call to IWMHeaderInfo3::GetAttributeCountEx where the stream number was set to 0xFFFF.

When setting attributes for MP3 files, the metadata editor will automatically insert a byte-order mark in accordance with the Unicode specification. If you manually insert a byte-order mark, this method will not fail, but the value will then have two marks, which can cause problems when reading the attribute.

The objects of the Windows Media Format SDK perform type checking on some supported metadata attributes, but not all of them. You should ensure that any attributes you use are set using the data type specified in the Attributes section of this documentation. Likewise, you cannot assume that an attribute set by another application will use the correct data type.


Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]


Windows Media Format 9 Series SDK, or later versions of the SDK


Wmsdkidl.h (include Wmsdk.h)


WMStubDRM.lib (if you use DRM)

See also

IWMHeaderInfo3 Interface