static extern int CoGetInterfaceAndReleaseStream(IStream pStm, [In] ref

static extern void CoMarshalHresult(UCOMIStream pStm, int hresult);

static extern int CoMarshalInterface(UCOMIStream pStm, [In] ref Guid riid,

   [MarshalAs(UnmanagedType.IUnknown)] object pUnk, out IStream ppStm);

static extern int CoUnmarshalHresult(UCOMIStream pStm);

static extern int CoUnmarshalInterface(UCOMIStream pStm, [In] ref Guid riid,

static extern int CoUnmarshalInterface(System.Runtime.InteropServices.ComTypes.IStream pStm, [In] ref Guid riid,

   out UCOMIStream ppstm);

    Declare Function CreateStreamOnHGlobal Lib "ole32" (ByVal hGlobal As IntPtr, ByVal fDeleteOnRelease As Boolean, ByRef ppstm As UCOMIStream) As Long

    extern public static int CreateStreamOnHGlobal(IntPtr ptr, bool delete, out System.Runtime.InteropServices.ComTypes.IStream pOutStm);

    public extern static void GetHGlobalFromStream(IStream stm, ref IntPtr hGlobal);

        IStream comStream;

            int SizeOfIstream = ByteSizeOfIPStreamInit(pPersistStream) * 2;  // two bytes per value -- See my OleSaveToStream (ole32)              

                IntPtr nativePtr = Marshal.AllocHGlobal(SizeOfIstream); //buffer.Length); // allocate space on the native heap

                Marshal.Copy(buffer, 0, nativePtr, SizeOfIstream);      // copy byte array to native heap

                if (CreateStreamOnHGlobal(nativePtr, true, out comStream) == S_OK) // Create IStream from allocated memory that has buffer data

static extern int OleLoadFromStream(System.Runtime.InteropServices.ComTypes.IStream pStm,

static extern int OleLoadFromStream(System.Runtime.InteropServices.ComTypes.IStream pStm,

    extern public static int CreateStreamOnHGlobal(IntPtr ptr, bool delete, out System.Runtime.InteropServices.ComTypes.IStream pOutStm);

    private static extern void OleSaveToStream(IPersistStreamInit pPStm, IStream pStm);

         IntPtr  ptrIStream = IntPtr.Zero;

         IStream IPtrStream;

         if (CreateStreamOnHGlobal(ptrIStream, true, out IPtrStream) == 0)

              iSzOfStreamInBytes = IStreamSizeRead(IPtrStream);

    public int IStreamSizeRead(IStream pOutStm)

    extern public static int CreateStreamOnHGlobal(IntPtr ptr, bool delete, out System.Runtime.InteropServices.ComTypes.IStream pOutStm);

    private static extern void OleSaveToStream(IPersistStreamInit pPStm, IStream pStm);

         IntPtr  ptrIStream = IntPtr.Zero;

         IStream IPtrStream;

         if (CreateStreamOnHGlobal(ptrIStream, true, out IPtrStream) == 0)

              iSzOfStreamInBytes = IStreamSizeRead(IPtrStream);

    public int IStreamSizeRead(IStream pOutStm)

static extern Guid ReadClassStm(UCOMIStream pStm);

    UCOMIStream pStm,

static extern void SHCreateStreamOnFileEx(string fileName, uint grfmode, uint dwAttributes, bool fCreate, System.Runtime.InteropServices.ComTypes.IStream streamNull, ref System.Runtime.InteropServices.ComTypes.IStream stream);

static extern IStream SHCreateStreamOnFileEx(string pszFile, uint grfMode, uint dwAttributes, bool fCreate, IStream pstmTemplate);

static extern void SHCreateStreamOnFileEx(string fileName, uint grfmode, uint dwAttributes, bool fCreate, System.Runtime.InteropServices.ComTypes.IStream streamNull, ref System.Runtime.InteropServices.ComTypes.IStream stream);

static extern int AVIFileCreateStream(IntPtr pfile, out IntPtr ppavi, ref AVISTREAMINFO psi);

Declare Function AVIFileCreateStream Lib "avifil32.dll" Alias "AVIFileCreateStreamA" (ByVal pfile As IntPtr, ByRef ppavi As IntPtr, ByRef psi As AVISTREAMINFO) As Integer

[DllImport("avifil32.dll", EntryPoint="AVIStreamInfo")]

static extern int AVIGetStreamInfo(IntPtr pavi, out AVISTREAMINFO psi, int lSize);

static extern TODO AVIStreamExit(TODO);

Declare Function AVIStreamExit Lib "avifil32.dll" (TODO) As TODO

static extern TODO AVIStreamGetFrameOpen(TODO);

    Public Shared Function AVIStreamGetFrameOpen(ByVal pAVIStream As IntPtr, _

static extern uint AVIStreamLength(IntPtr pavi);

Declare Function AVIStreamLength Lib "avifil32.dll" (TODO) As TODO

static extern int AVIStreamReadFormat(IntPtr pavi, int lPos, out WAVEFORMATEX lpFormat, out int lpcbFormat);

    <DllImport("avifil32.dll", entrypoint:="AVIStreamReadFormat")> _

      Public Shared Function AVIStreamReadFormat(ByVal aviStream As IntPtr,

    Public Shared Function AVIStreamReadFormat(ByVal aviStream As IntPtr,

    Public Shared Function AVIStreamReadFormat2(ByVal aviStream As IntPtr, ByVal lPos As Int32, ByRef lpFormat As BITMAPINFOHEADER, ByRef cbFormat As Int32) As Integer

    Dim hr As Integer = AVIStreamReadFormat(aviStream, lPos, lpFormat, cbFormat)

static extern int AVIStreamReadFormat(IntPtr pavi, int lPos, out WAVEFORMATEX lpFormat, out int lpcbFormat);

    <DllImport("avifil32.dll", entrypoint:="AVIStreamReadFormat")> _

      Public Shared Function AVIStreamReadFormat(ByVal aviStream As IntPtr,

    Public Shared Function AVIStreamReadFormat(ByVal aviStream As IntPtr,

    Public Shared Function AVIStreamReadFormat2(ByVal aviStream As IntPtr, ByVal lPos As Int32, ByRef lpFormat As BITMAPINFOHEADER, ByRef cbFormat As Int32) As Integer

    Dim hr As Integer = AVIStreamReadFormat(aviStream, lPos, lpFormat, cbFormat)

static extern int AVIStreamRelease(IntPtr pavi);

Declare Function AVIStreamRelease Lib "avifil32.dll" (pavi As IntPtr) As Integer

    void Load ([InAttribute] IStream pstm);

    void Save ([InAttribute] IStream pstm, [InAttribute] int fClearDirty);

    void Load ([InAttribute] IStream pstm);

    void Save ([InAttribute] IStream pstm, [InAttribute] int fClearDirty);

    void Load ([InAttribute] IStream pstm);

    void Save ([InAttribute] IStream pstm, [InAttribute] int fClearDirty);

        /* [out] */ out IStream ppstm);

        /* [out] */ out IStream ppstm);

                     ByRef ppstm As IStream)

                   ByRef ppstm As IStream)

public interface IStream

      void CopyTo(IStream pstm, long cb, out long pcbRead, out long pcbWritten);

      void Clone(out IStream ppstm);

[System.Runtime.InteropServices.ComTypes.IStream] in the .NET Framework 2.0.

The Seek and CopyTo methods are documented as allowing NULL to be passed instead of output parameters, if the caller does not care what the result was. If you have consumers of your IStream that use it in this manner, you will need to replace the affected definitions with IntPtr values and use Marshal.WriteInt64() to assign them:

     HRESULT LoadSettingsFromStream([MarshalAs(UnmanagedType.Interface)] IStream pStream);

     HRESULT SaveSettingsToStream([MarshalAs(UnmanagedType.Interface)] IStream pStream);

        [Out, MarshalAs(UnmanagedType.Interface)] out object iStream);

        [In, MarshalAs(UnmanagedType.Interface)] object iStream);

   IntPtr ppIRAPIStream,

#ifndef RAPISTREAMFLAG

typedef enum tagRAPISTREAMFLAG

} RAPISTREAMFLAG;

DECLARE_INTERFACE_ (IRAPIStream, IStream )

    STDMETHOD(SetRapiStat)(THIS_ RAPISTREAMFLAG Flag, DWORD dwValue) PURE;

    STDMETHOD(GetRapiStat)(THIS_ RAPISTREAMFLAG Flag, DWORD *pdwValue) PURE;

__declspec (dllexport) INT MyFunction( DWORD, BYTE*, DWORD*, BYTE*, IRAPIStream *, PVOID );

INT MyFunction( DWORD cbInput, BYTE pInput, DWORD pcbOutput, BYTE *ppOutput, IRAPIStream *pStream, PVOID reserved )

    out UCOMIStream stream, Int32 dwReserved, IntPtr lpfnCB);

    STREAM = &H400000          '   supports BindToObject(IID_IStream)

        SFGAO_STREAM        = 0x00400000,         // supports BindToObject(IID_IStream)

public struct AVISTREAMINFO

Structure AVISTREAMINFO

    //     The storage medium is a stream object identified by an IStream pointer. Use

    //     member is not null, the destination process should use IStream::Release to

    TYMED_ISTREAM = 4,

    '     The storage medium is a stream object identified by an IStream pointer. Use

    '     member is not null, the destination process should use IStream::Release to

    TYMED_ISTREAM = 4

  /*[MarshalAs(UnmanagedType.Interface)]*/ out IStream ppXmlStream);

    private const uint MIDICAPS_STREAM = 8;      // driver supports midiStreamOut directly

extern static Int32 midiStreamClose(IntPtr hMidiStream);

Public Declare Function midiStreamClose Lib "winmm.dll" (ByVal hMidiStream As IntPtr) As Integer

extern static Int32 midiStreamOpen(ref IntPtr hMidiStream, ref Int32 puDeviceID, Int32 cMidi, IntPtr dwCallback, IntPtr dwInstance, Int32 fdwOpen);

Public Declare Function midiStreamOpen Lib "winmm.dll" (ByVal hMidiStream As IntPtr, ByVal puDeviceId As IntPtr, ByVal cMidi As Integer, ByVal dwCallback As IntPtr, ByVal dwInstance As IntPtr, ByVal fdwOpen As Integer) As Integer

static extern Int32 midiStreamOut(IntPtr hMidiStream, MIDIHDR lpMidiHdr, uint cbMidiHdr);

Declare Function midiStreamOut Lib "winmm.dll" (ByVal hMidiStream As IntPtr, ByVal lpMidiHdr As MIDIHDR, ByVal cbMidiHdr As UInteger) As Integer

static extern Int32 midiStreamPause(IntPtr hMidiStream);

Declare Function midiStreamPause Lib "winmm.dll" (ByVal hMidiStream As IntPtr) As Integer

static extern TODO midiStreamPosition(TODO);

Declare Function midiStreamPosition Lib "winmm.dll" (ByVal hms As IntPtr, ByVal pmmt As MMTIME, ByVal cbmmt As UInteger) As Integer

static extern TODO midiStreamProperty(TODO);

Declare Function midiStreamProperty Lib "winmm.dll" (TODO) As TODO

static extern Int32 midiStreamRestart(IntPtr hMidiStream);

static extern Int32 midiStreamStop(IntPtr hMidiStream);