Show Me the Movie with DirectShow

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Creating a GUI-Based Media Player with an Integrated Video Renderer Window

The filter graph manager inserts a video renderer into the filter graph when hdshow is instructed to present a video. The video renderer defaults to running in windowed mode, where it creates a window and paints video frames onto that window's surface. Unless otherwise specified, this window is a top-level window with its own borders and a title bar (which displays ActiveMovie Window).

When you're creating a media player application, you'll probably want to integrate the video renderer's window into your application's user interface rather than rely on the aforementioned top-level window. You can accomplish this task by attaching the video renderer's window to the application window, which is what Listing 2's mp1.cpp source code demonstrates.

Listing 2 mp1.cpp

// mp1.cpp

// Media Player #1

#include <control.h>
#include <io.h>    // Allow access to MAXPATH, MAXFILE, and MAXEXT constants.
#include <iostream.h>
#include <strmif.h>
#include <uuids.h>

#include "mp1.h"

#define OAFALSE 0
#define OATRUE -1

#pragma resource "mp1.res"

char g_szAppName [] = "mp1";

IGraphBuilder *g_pGraph;

IMediaControl *g_pControl;

IVideoWindow *g_pVidWin;

void Cleanup (void)
{
  if (g_pControl != NULL)
    g_pControl->Stop ();

  if (g_pVidWin != NULL)
  {
    g_pVidWin->put_Visible (OAFALSE); // Hide video renderer's window to 
                     // prevent momentary video image
                     // flicker.
    g_pVidWin->put_Owner (NULL);
    g_pVidWin->Release ();
    g_pVidWin = NULL;
  }

  if (g_pControl != NULL)
  {
    g_pControl->Release ();
    g_pControl = NULL;
  }

  if (g_pGraph != NULL)
  {
    g_pGraph->Release ();
    g_pGraph = NULL;
  }
}

void PlayFile (HWND hWnd, LPSTR szMediaPath)
{
  Cleanup ();

  HRESULT hr = CoCreateInstance (CLSID_FilterGraph, NULL,
                 CLSCTX_INPROC_SERVER, IID_IGraphBuilder,
                 (LPVOID *) &g_pGraph);
  if (FAILED (hr))
  {
    MessageBox (hWnd, "CoCreateInstance() failure", g_szAppName, MB_OK);
    return;
  }

  hr = g_pGraph->QueryInterface (IID_IMediaControl, (LPVOID *) &g_pControl);
  if (FAILED (hr))
  {
    MessageBox (hWnd, "unable to obtain IMediaControl interface",
          g_szAppName, MB_OK);
    return;
  }

  hr = g_pGraph->QueryInterface (IID_IVideoWindow, (LPVOID *) &g_pVidWin);
  if (FAILED (hr))
  {
    MessageBox (hWnd, "unable to obtain IVideoWindow interface",
          g_szAppName, MB_OK);
    return;
  }

  WCHAR wPath [MAXPATH];
  MultiByteToWideChar (CP_ACP, 0, szMediaPath, -1, wPath, MAXPATH);

  hr = g_pGraph->RenderFile (wPath, NULL);
  if (SUCCEEDED (hr))
  {
    g_pVidWin->put_Owner ((OAHWND) hWnd);
    g_pVidWin->put_WindowStyle (WS_CHILD | WS_CLIPSIBLINGS);
    g_pVidWin->put_Visible (OATRUE);

    SendMessage (hWnd, WM_SIZE, 0, 0);

    hr = g_pControl->Run ();
    if (FAILED (hr))
      MessageBox (hWnd, "unable to run media", g_szAppName, MB_OK);
  }
  else
    MessageBox (hWnd, "unable to render media", g_szAppName, MB_OK);
}

LRESULT CALLBACK WndProc (HWND hWnd, int iMsg, WPARAM wParam, LPARAM lParam)
{
  LPSTR lpstrFilter = "Media files (*.mpg, *.avi, *.wmv, *.mp3, *.wma)\0"
            "*.mpg;*.avi;*.wmv;*.mp3;*.wma\0"
            "All files (*.*)\0"
            "*.*\0"
            "\0";

  switch (iMsg)
  {
   case WM_COMMAND:
      switch (LOWORD (wParam))
      {
       case IDM_FILE_EXIT:
          SendMessage (hWnd, WM_CLOSE, 0, 0);
          return 0;

       case IDM_FILE_OPEN:
          char szFilename [MAXPATH];
          szFilename [0] = '\0';

          char szTitlename [MAXPATH];
          szTitlename [0] = '\0';

          OPENFILENAME ofn;
          ofn.lStructSize = sizeof (OPENFILENAME);
          ofn.hwndOwner = hWnd;
          ofn.hInstance = NULL;
          ofn.lpstrFilter = lpstrFilter;
          ofn.lpstrCustomFilter = NULL;
          ofn.nMaxCustFilter = 0;
          ofn.nFilterIndex = 1;
          ofn.lpstrFile = szFilename;
          ofn.nMaxFile = MAXPATH;
          ofn.lpstrFileTitle = szTitlename;
          ofn.nMaxFileTitle = MAXFILE+MAXEXT;
          ofn.lpstrInitialDir = NULL;
          ofn.lpstrTitle = NULL;
          ofn.Flags = OFN_HIDEREADONLY | OFN_PATHMUSTEXIST;
          ofn.nFileOffset = 0;
          ofn.nFileExtension = 0;
          ofn.lpstrDefExt = NULL;
          ofn.lCustData = 0;
          ofn.lpfnHook = NULL;
          ofn.lpTemplateName = NULL;
          if (!GetOpenFileName (&ofn))
            return 0;

          PlayFile (hWnd, szTitlename);
          return 0;
      }
      break;

   case WM_DESTROY:
      Cleanup ();
      PostQuitMessage (0);
      return 0;

   case WM_MOVE:
      if (g_pVidWin != NULL)
        g_pVidWin->NotifyOwnerMessage ((OAHWND) hWnd, iMsg, wParam,
                       lParam);
      return 0;

   case WM_SIZE:
      if (g_pVidWin != NULL)
      {
        RECT rc;
        GetClientRect (hWnd, &rc);
        g_pVidWin->SetWindowPosition (0, 0, rc.right, rc.bottom);
      }
      return 0;
  }

  return DefWindowProc (hWnd, iMsg, wParam, lParam);
}

#pragma argsused
int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hInstancePrev,
          LPSTR lpszCmdLine, int iCmdShow)
{
  if (FAILED (CoInitialize (NULL)))
  {
    cerr << "CoInitialize() failure\n";
    return -1;
  }

  WNDCLASSEX wc;
  wc.cbSize = sizeof (WNDCLASSEX);
  wc.style = CS_HREDRAW | CS_VREDRAW;
  wc.lpfnWndProc = (WNDPROC) WndProc;
  wc.cbClsExtra = 0;
  wc.cbWndExtra = 0;
  wc.hInstance = hInstance;
  wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);
  wc.hCursor = LoadCursor (NULL, IDC_ARROW);
  wc.hbrBackground = (HBRUSH) GetStockObject (BLACK_BRUSH);
  wc.lpszMenuName = g_szAppName;
  wc.lpszClassName = g_szAppName;
  wc.hIconSm = LoadIcon (NULL, IDI_APPLICATION);

  RegisterClassEx (&wc);

  HWND hWnd = CreateWindowEx (0, g_szAppName, "Media Player #1",
                WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN,
                CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
                CW_USEDEFAULT, NULL, NULL, hInstance, NULL);

  ShowWindow (hWnd, iCmdShow);
  UpdateWindow (hWnd);

  MSG msg;
  while (GetMessage (&msg, NULL, 0, 0 ))
  {
   TranslateMessage (&msg);
   DispatchMessage (&msg);
  }

  CoUninitialize ();

  return msg.wParam;
}

Unlike Listing 1, which describes a console application (the presence of the main() function gives this kind of application away), Listing 2 describes a GUI application with a WinMain() entry-point function and a window procedure (WndProc()) for processing messages sent to it from Windows or elsewhere in the application.

The WinMain() function is tasked with initializing COM via CoInitialize(). If this isn't possible, there's no point in proceeding, so the application exits. After initializing and registering the application's main window class, WinMain() creates and displays this window, and enters a message loop to process messages. When this loop exits, WinMain() uninitializes COM and also exits.

In response to the user selecting the Open menu item from the File menu, WndProc() receives a WM_COMMAND message with wParam set to IDM_FILE_OPEN. The message handler presents the user with a dialog box for selecting a media file and invokes PlayFile() with this media file's complete path (placed in szTitlename).

PlayFile() first obtains the filter graph manager's IGraphBuilder interface so that it can access additional interfaces and build the filter graph. This function next obtains the IMediaControl interface, so that it can run the filter graph, and the IVideoWindow interface, so that it can attach the video renderer's window to the application window, as follows:

• In response to RenderFile() succeeding, specify a parent window for the video renderer's window by invoking IVideoWindow's HRESULT put_Owner(OAHWND Owner) method with the application's window handle.
• Set the WS_CHILD and WS_CLIPSIBLINGS styles on the video renderer's window by invoking IVideoWindow's HRESULT put_WindowStyle(long WindowStyle) method.

The WS_CHILD style specifies that the window is to be a child window, and the WS_CLIPSIBLINGS style specifies that the window is to be prevented from drawing inside the client area of another child window.

• Show the video renderer's window by passing OATRUE to IVideoWindow's HRESULT put_Visible(long Visible) method.
• Set the position of the video renderer's window relative to the application window's client area by invoking SendMessage(hWnd, WM_SIZE, 0, 0). This message's handler invokes GetClientRect() to obtain the client area coordinates, and invokes IVideoWindow's HRESULT SetWindowPosition(long Left, long Top, long Width, long Height) method to assign these coordinates to the video renderer's window.

Additionally, WM_MOVE messages sent to the application's window procedure are forwarded to the video renderer's window, by invoking IVideoWindow's HRESULT NotifyOwnerMessage(OAHWND hwnd, long uMsg, LONG_PTR wParam, LONG_PTR lParam) method. This method gives the video renderer an opportunity to reposition its window within the application's client area boundaries.

Unlike in Listing 1, you'll notice that it's not necessary to obtain an IMediaEvent and invoke its WaitForCompletion() method to wait until the media finishes playing. In contrast with a console application's main thread, which exits when the main() function exits, a GUI application's main thread only exits following the message loop, and the user decides when the message loop ends.

Specifically, the user selects Exit from the File menu. In response, WndProc() receives a WM_COMMAND message with wParam set to IDM_FILE_EXIT. This message handler invokes SendMessage(hWnd, WM_CLOSE, 0, 0), which (thanks to DefWindowProc()) results in DestroyWindow() being invoked.

DestroyWindow() sends a WM_DESTROY message to WndProc(). Its message handler invokes PostQuitMessage(0) after cleaning up DirectShow resources via Cleanup()—this function stops the graph if it's running before resetting the video renderer window's owner to NULL, to prevent window messages from possibly being sent to the wrong window (resulting in errors).

PostQuitMessage() posts a WM_QUIT message to the calling thread's message queue. When this message is retrieved by GetMessage(), this function returns FALSE, which causes the message loop to exit. The 0 value passed to PostQuitMessage() specifies an application exit code and is the value placed in the WM_QUIT message's wParam field, which WinMain() returns.

Listing 3 shows the contents of the mp1.h header file.

Listing 3 mp1.h

// mp1.h

#define IDM_FILE_EXIT 100
#define IDM_FILE_OPEN 101

You might have noticed the #pragma resource "mp1.res" directive in Listing 2. This directive embeds compiled resources into the final EXE. Listing 4 presents the mp1.rc source for these compiled resources.

Listing 4 mp1.rc

// mp1.rc

#include "mp1.h"

mp1 MENU
{
  POPUP "&File"
  {
   MENUITEM "&Open...", IDM_FILE_OPEN
   MENUITEM "E&xit",  IDM_FILE_EXIT
  }
}

Assuming that you install Borland C++ 5.5.1 and set up your environment per the Borland C++ 5.5.1 article's instructions, invoke the command lines below to create mp1.res followed by mp1.exe:

brc32 -r mp1.rc
bcc32 -tW -I..\..\include -L..\..\lib mp1.cpp

In the first command line, -r means to compile only; don't bind resources to the EXE. In the second command line, -tW means that the source code contains a WinMain() function and that a GUI-mode Win32 application is being created.

Specify mp1 on the command line or double-click mp1.exe in Windows Explorer to launch this application. You'll observe a window with a menu bar (for choosing a media file and ending the application) and a content area (for viewing video-based media).