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Working with Metadata

Metadata support is provided by the writer object, the reader and synchronous reader objects, and the metadata editor object. For general information about metadata, see Metadata. For information about the features supporting metadata in the Windows Media Format SDK, see Metadata Features.

The interface for metadata editing is IWMHeaderInfo3, which you can obtain by calling the QueryInterface method of any interface in one of the objects listed above. IWMHeaderInfo3 inherits the methods of IWMHeaderInfo and IWMHeaderInfo2. The methods of IWMHeaderInfo3 that deal with metadata attributes represent a different approach to accessing metadata than that used by the methods of IWMHeaderInfo. You should always use the newer methods.

Metadata in an ASF file is identified by an index and a stream number. File-level attributes are assigned a stream number of 0. In previous versions of the Windows Media Format SDK, attributes could be identified by name. However, because you can now duplicate attribute names within a stream, this is no longer possible. Instead, you can retrieve all the indexes matching a name. For more information, see Retrieving Metadata Attributes.

To aid in finding attributes quickly, you can use a special stream number, 0xFFFF. Use this stream number to identify the file as a whole, rather than a specific stream or the file-level attributes. The objects of the Windows Media Format SDK maintain separate indexes for each stream and for the file-level attributes. When using stream 0xFFFF, the indexes are different from those you use when specifying a specific stream. For example, the attribute that is index 0 for stream 0 will not be the same as the attribute that is index 0 for stream 0xFFFF.

The following sections describe the use of metadata in greater detail.

Section Description
Retrieving Metadata Attributes Describes how to read metadata attributes from a file header.
Setting Metadata Attributes Describes how to add new metadata attributes to a file header.
Editing Metadata Attributes Describes how to edit existing metadata attributes.
Removing Metadata Attributes Describes how to remove existing metadata attributes.
Using Complex Metadata Attributes Describes how to work with attributes whose values are represented by structures.

 

Several of the sample applications show how to retrieve and edit metadata. In particular, see the MetadataEdit sample, which comes in both C++ and C# versions.

Related topics

Attributes
Programming Guide
Sample Applications

 

 

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