首先，我保证使用一下方法是可行的。步骤如下：

1、修改cygwin文件的环境配置。在cygwin的etc文件夹下的profile文件中添加如下语句，

export PATH=$PATH:"/cygdrive/c/Program Files/Microsoft Visual Studio/COMMON/MSDev98/Bin":"/cygdrive/c/Program Files/Microsoft Visual Studio/VC98/Bin"
export INCLUDE='C:/Program Files/Microsoft Visual Studio/VC98/Include'
export MIDL="midl"

添加完成后，重新启动cygwin，运行midl命令，如果出现：

Microsoft (R) MIDL Compiler Version 5.01.0164
Copyright (c) Microsoft Corp 1991-1997. All rights reserved.
midl : command line error MIDL1000 : missing source-file name

则表示修改cygwin成功。

2、在axvlc.idl文件中添加语句：       

HRESULT snapcount([in] int counts);

在axvlc_idl.h文件中添加

virtual HRESULT STDMETHODCALLTYPE snapcount(
        int counts) = 0;

HRESULT (STDMETHODCALLTYPE *snapcount)(
        IVLCControl* This,
        int counts);

#define IVLCControl_snapcount(p,a) (p)->lpVtbl->snapcount(p,a)

在vlccontrol.cpp文件中添加：

STDMETHODIMP VLCControl::snapcount(int counts)
{
    HRESULT result = E_UNEXPECTED;
    if( _p_instance->isRunning() )
    {
        int i_vlc;
        result = _p_instance->getVLCObject(&i_vlc);
        if( SUCCEEDED(result) )
        {
            VLC_TimeSet(i_vlc, counts, VLC_TRUE);
        }
    }
    return result;
};

在vlccontrol.h文件中添加

    STDMETHODIMP snapcount(int counts);

3、在cygwin环境下，到activex目录下，运行midl axvlc.idl命令，如果出现：

$ midl axvlc.idl
Microsoft (R) MIDL Compiler Version 5.01.0164
Copyright (c) Microsoft Corp 1991-1997. All rights reserved.
Processing ./axvlc.idl
axvlc.idl
Processing C:/Program Files/Microsoft Visual Studio/VC98/Include/oaidl.idl
oaidl.idl
Processing C:/Program Files/Microsoft Visual Studio/VC98/Include/objidl.idl
objidl.idl
Processing C:/Program Files/Microsoft Visual Studio/VC98/Include/unknwn.idl
unknwn.idl
Processing C:/Program Files/Microsoft Visual Studio/VC98/Include/wtypes.idl
wtypes.idl

nst@nst330 ~/vlc-0.8.6b/activex

则表示成功添加成功。

4、然后在目录下运行make命令，如果编译成功。

在控件中就成功的添加了一个新的接口snapcount。