The Async sample filter does not support AVI files, because it cannot connect to the AVI Splitter filter. The Async filter's output pin proposes MEDIATYPE_Stream and MEDIASUBTYPE_NULL for the media type. The input pin on the AVI Splitter filter does not accept MEDIASUBTYPE_NULL, and does not propose any types of its own. Therefore, the pin connection fails. The Async filter could be enhanced to offer MEDIASUBTYPE_Avi when appropriate. For example, it could examine the file format, or use the file extension.