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The DirectShow SDK and the Windows Media Format SDK

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[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

DirectShow and the Windows Media Format SDK offer complementary solutions for writing applications that create and play back Windows Media Format streams. For more information, see the "Audio and Video" section of the MSDN Library.

The ASF Writer filter accepts any number of input streams and creates an ASF file. The filter uses the Windows Media Format SDK to convert uncompressed audio or video files to Windows Media-based content. The compressed content is then stored in the ASF container format. If the content is audio only, then the file is given a .wma extension and is referred to as a Windows Media Audio file. If the content is video only or video and audio, then the file is given a .wmv extension and is referred to as a Windows Media Video file. Either type of file may also include metadata.

You can use the WM ASF Writer in various scenarios including digital video (DV) capture, audio recompression, and conversion of Audio-Video Interleaved (AVI) or MPEG multimedia files for network streaming. This filter provides the only way to create Microsoft® Windows Media™ Audio (WMA) and Windows Media Video (WMV) files in DirectShow®. The filter can also create files that are secured by Digital Rights Management (DRM), and can also create MPEG-4 content using the Microsoft MPEG-4 Encoder. This content is stored in the ASF container format.

Creating ASF Files in DirectShow