Displaying WMV from a stream with the WM ASF Reader Filter in a filter graph

From: Bob Dellaca (bobdlxyzzy_at_xtra.co.nz)
Date: 01/12/05

  • Next message: joealey2003_at_yahoo.com: "Multiple RSA private key on same Https" 
    Date: Wed, 12 Jan 2005 15:38:42 +1300

    This is a follow-up to a thread started in this group last October by
    Dale Ingold (now lost from my news server).

    Here is one way to get the WM ASF Reader filter in a filter graph to
    accept WMV or ASF input from a stream. In brief, it involves defining
    your own "custom file type" as a "protocol" and getting the ASF Reader
    filter to accept an IStream from your application when the filter is
    asked to render a file of that custom protocol. Two registry keys need
    to be added and a short DLL needs to be written; other than that, the
    application needs to be able to supply an IStream interface object
    when the filter graph is built.

    This works with version 9 of DirectX.

    Select your own protocol name such as "myProt", so that the ASF Reader
    filter can be asked to render a file such as "myProt://something".

    1. As listed in the DirectShow SDK Help, register the protocol under
    the key

    HKEY_CLASSES_ROOT\myProt

    with a (string) entry named "Source Filter" for the GUID for the WM
    ASF Reader filter

    Source Filter = {187463A0-5BB7-11D3-ACBE-0080C75E246E}

    2. As listed in the WM SDK WMFormat Help, register a DLL as a Source
    Plug-in for the myProt protocol under the key

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows Media\WMSDK\sources

    with a (string) entry, let's call it "myProt", for the full filename
    of the DLL (here named "myProt")

    myProt = c:\fullpathname\myProt.dll

    3. Create a DLL, here named myProt, that exports the function
    WMCreateStreamForURL

    library myProt;

    function WMCreateStreamForURL(pwszURL: PWideChar;
                                  out pfCorrectSource: BOOL;
                                  var pStream: IStream): HRESULT; stdcall;

    exports
      WMCreateStreamForURL;

    As listed in the WM SDK, WMCreateStreamForURL has to output a pointer
    to an IStream if it can handle the input "file". Thus, if the myProt
    DLL sees a file named "myProt://something" it should set
    pfCorrectSource to True and set pStream to point to the IStream;
    otherwise it should set pfCorrectSource to False and set pStream to
    nil.

    4. In the application, define an IStream interface object, create an
    instance of it, create a filter graph, and render a "file" of the
    "myProt" protocol "somehow" passing the derived IStream object pointer
    to the WMCreateStreamForURL function in the DLL (one method is to
    include the address of the IStream in the file "name" - the "file"
    might then be for example "myProt://$9e4238")

    type
      TmyProtStream = class(TInterfacedObject, IStream)
          [...]
      end;

    var
      myProtStream: TmyProtStream;
      pBuild: ICaptureGraphBuilder2;
      pGraph: IGraphBuilder;
      aFileName: string;
      wFileName: WideString;
    begin
      myProtStream := TmyProtStream.Create(...);
      CoCreateInstance(CLSID_FilterGraph, nil, CLSCTX_INPROC_SERVER,
                       IID_IFilterGraph2, pGraph);
      CoCreateInstance(CLSID_CaptureGraphBuilder2, nil,
                       CLSCTX_INPROC_SERVER,
                       IID_ICaptureGraphBuilder2, pBuild);
      pBuild.SetFiltergraph(pGraph);
      [add other filters]
      aFileName := Format('myProt://$%x', [Integer(myProtStream as

    IStream)]);
      wFileName := aFileName;
      pGraph.RenderFile(@wFileName[1], nil);
      [...]
      pGraph := nil;

    The IStream methods Read, Seek & Stat are called by the ASF Reader
    filter; it appears that the other methods can be written as not
    implemented. It also appears that the ASF Reader filter releases the
    IStream interface when the filter graph is released (as one might hope
    for but not necessarily see), so that there is no need to free or
    release myProtStream in the above example.

    If anyone is interested, I can post some sample code.

    Bob Dellaca

  • Next message: joealey2003_at_yahoo.com: "Multiple RSA private key on same Https"

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