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Posted 3 Jan 2005

Using the DirectShow Video Mixing Renderer 9 filter

, 1 Feb 2005
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This article describes how to dynamically mix two video files (.mpeg, .mpg, .avi and .dat). Mixing involves alpha-blending and stretching/shrinking and positioning of the two video streams, individually, using DirectShow's VMR9 filter.

Sample Image - DirectShowVMR91.jpg


This article shows the steps involved in creating and configuring DirectShow’s Video Mixing Renderer Filter 9 (VMR9). The two video streams, one on top of the other, are rendered on a single surface. This surface, in our case, is a PictureBox control. Each stream's alpha value, position and height/width can be adjusted at runtime.

How VMR9 is different

The following diagrams show the difference between rendering two videos with VMR9 and without VMR9.

Without VMR9

Rendering without VMR9

We notice that simply rendering two videos will result in two separate Video Renderers, which means that the videos are being played on two separate surfaces.

With VMR9

Rendering with VMR9

In this case, the VMR9 filter directs both video streams into its own input pins. This means there is only one renderer, and thus a single rendering surface for both video streams.

The Working

To enhance reusability and readability factors, the functionality of the VMR9 filter has been encapsulated inside a class named myVMR9.

The myVMR9 class

This class has the following private data members:

  • VMR9NormalizedRect *r;
  • IVMRWindowlessControl9 *pWC;
  • IVMRMixerControl9 *pMix;
  • IGraphBuilder *pGB;
  • IBaseFilter *pVmr;
  • IVMRFilterConfig9 *pConfig;
  • IMediaControl *pMC;
  • IMediaSeeking *pMS;

The constructor

The constructor receives a PictureBox's coordinates of type System::Drawing::Rectangle, along with its handler of type HWND. These two attributes are used by VMR9 for rendering purposes.

public: myVMR9(System::Drawing::Rectangle rect, HWND hwnd)
    // initialize video coordinates with normal values
    r = new VMR9NormalizedRect;
    r->left = 0;
    r->top = 0;
    r->right = 1;
    r->bottom = 1;

    pWC = NULL;
    pMix = NULL;
    pGB = NULL;
    pVmr = NULL;
    pConfig = NULL;
    pMC = NULL;
    pMS = NULL;
    // create an instance of the Filter Graph Manager
    CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, 
        IID_IGraphBuilder, (void **)&pGB);
    // create an instance of the VMR9 filter
    CoCreateInstance(CLSID_VideoMixingRenderer9, NULL, CLSCTX_INPROC,
        IID_IBaseFilter, (void**)&pVmr);
    // add the VMR9 filter to the Graph Manager
    pGB->AddFilter(pVmr, L"Video");    
    // get a pointer to the IVMRFilterConfig9 interface
    pVmr->QueryInterface(IID_IVMRFilterConfig9, (void**)&pConfig);
    // make sure VMR9 is in windowless mode
    // get a pointer to the IVMRWindowlessControl9 interface 
    pVmr->QueryInterface(IID_IVMRWindowlessControl9, (void**)&pWC);
    // explicitly convert System::Drawing::Rectangle type to RECT type
    RECT rcDest = {0};
    rcDest.bottom = rect.Bottom;
    rcDest.left = rect.Left;
    rcDest.right = rect.Right; = rect.Top;

    // set destination rectangle for the video
    pWC->SetVideoPosition(NULL, &rcDest);

    // specify the container window that the video should be clipped to    
    // IVMRMixerControl manipulates video streams
    pVmr->QueryInterface(IID_IVMRMixerControl9, (void**)&pMix);
    // IMediaSeeking seeks to a position in the video stream
    pGB->QueryInterface(IID_IMediaSeeking, (void **)&pMS);
    // IMediaControl controls flow of data through the graph
    pGB->QueryInterface(IID_IMediaControl, (void **)&pMC);

The methods

HRESULT play()
    pMC->Run(); return

HRESULT pause()
    return S_OK;

HRESULT stop()
    LONGLONG pos = 0;
    pMS->SetPositions(&pos, AM_SEEKING_AbsolutePositioning, 
    return S_OK;

HRESULT close()
    // make sure resources are freed
    return S_OK;

HRESULT setAlpha(DWORD stream, float alpha)
    // set alpha of specified video stream
    pMix->SetAlpha(stream, alpha);
    return S_OK;

HRESULT setX(DWORD stream, float x)
    // video displacement along x-axis
    r->right = x + (r->right - r->left);
    r->left = x;
    pMix->SetOutputRect(stream, r);
    return S_OK;

HRESULT setY(DWORD stream, float y)
    // video displacement along y-axis
    r->bottom = y + (r->bottom - r->top);
    r->top = y;
    pMix->SetOutputRect(stream, r);
    return S_OK;

HRESULT setW(DWORD stream, float w)
    // video stretching/shrinking along x-axis
    r->right = r->left + w;
    pMix->SetOutputRect(stream, r);
    return S_OK;

HRESULT setH(DWORD stream, float h)
    // video stretching/shrinking along y-axis
    r->bottom = r->top + h;
    pMix->SetOutputRect(stream, r);
    return S_OK;

HRESULT renderFiles(String* file1, String* file2)
    // convert String type to LPCSTR type and render the videos
    LPCTSTR lFile;
    lFile = 
      static_cast<LPCTSTR>(const_cast<void*>(static_cast<const void*>
    pGB->RenderFile((LPCWSTR)lFile, NULL);
    lFile = 
      static_cast<LPCTSTR>(const_cast<void*>(static_cast<const void*>
    pGB->RenderFile((LPCWSTR)lFile, NULL);
      (static_cast<const void*>(lFile))));
    return S_OK;

Now that the VMR9's functionality has been separated from the GUI, Button and TrackBar handlers can simply create a pointer to a myVMR9 object and call the required methods.

Sample screenshot

Additional Information

  • The second video stream opened is on top of the first one, i.e., file-2 video is rendered on top of file-1 video. Therefore, if the first video's alpha value is a 100% and the second video's alpha value is 50%, then both videos will be equally (50%) visible.
  • It should be noted that the values of Width and Height of trackbars can run into negative values. So when a video stream's width is -100%, it is laterally inverted. Similarly, when a video stream's height is -100%, the video is upside down.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Sameer Ahmed
Software Developer
Pakistan Pakistan
No Biography provided

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Comments and Discussions

GeneralRe: VB6 or VB.NET? Pin
Xristos20004-Sep-07 1:56
memberXristos20004-Sep-07 1:56 
Questionlnk error: _check_commonlanguageruntime_version Pin
jz.tan16-Aug-07 0:51
memberjz.tan16-Aug-07 0:51 
AnswerRe: lnk error: _check_commonlanguageruntime_version Pin
Sameer Ahmed16-Aug-07 11:48
memberSameer Ahmed16-Aug-07 11:48 
GeneralRe: lnk error: _check_commonlanguageruntime_version Pin
jz.tan16-Aug-07 16:40
memberjz.tan16-Aug-07 16:40 
GeneralRe: lnk error: _check_commonlanguageruntime_version Pin
Sameer Ahmed17-Aug-07 1:07
memberSameer Ahmed17-Aug-07 1:07 
GeneralRe: lnk error: _check_commonlanguageruntime_version Pin
jz.tan23-Aug-07 21:04
memberjz.tan23-Aug-07 21:04 
GeneralMerit Pin
jdsc5-Jun-07 1:16
memberjdsc5-Jun-07 1:16 
GeneralRe: Merit Pin
Sameer Ahmed6-Jun-07 5:45
memberSameer Ahmed6-Jun-07 5:45 
GeneralLINKER errors in VC++6.0 Pin
manas_hit31-May-07 0:49
membermanas_hit31-May-07 0:49 
GeneralRe: LINKER errors in VC++6.0 Pin
Sameer Ahmed31-May-07 2:10
memberSameer Ahmed31-May-07 2:10 
QuestionCan a filter graph both VMR7 and VMR9? Pin
Manu Ranjana7-Jan-07 19:59
memberManu Ranjana7-Jan-07 19:59 
QuestionIssue with continuously adding and deleting VMR9s Pin
Manu Ranjana5-Jan-07 23:30
memberManu Ranjana5-Jan-07 23:30 
AnswerRe: Issue with continuously adding and deleting VMR9s Pin
Manu Ranjana7-Jan-07 19:54
memberManu Ranjana7-Jan-07 19:54 
GeneralSend the result of VMR9 to an .avi file Pin
cjacquel200727-Dec-06 9:01
membercjacquel200727-Dec-06 9:01 
GeneralRe: Send the result of VMR9 to an .avi file Pin
tanvon malik25-Sep-07 3:09
membertanvon malik25-Sep-07 3:09 
QuestionRe: Send the result of VMR9 to an .avi file Pin
boopathi_tpgit25-Sep-07 21:04
memberboopathi_tpgit25-Sep-07 21:04 
AnswerRe: Send the result of VMR9 to an .avi file Pin
tanvon malik25-Sep-07 22:14
membertanvon malik25-Sep-07 22:14 
Generalgreenish lines on video using VMR9 Pin
shovit25-Oct-06 21:29
membershovit25-Oct-06 21:29 
GeneralFull Screen [modified] Pin
alanmark5-Oct-06 5:02
memberalanmark5-Oct-06 5:02 
Questionenumerate pins Pin
Fariha Atta1-Oct-06 18:57
memberFariha Atta1-Oct-06 18:57 
AnswerRe: enumerate pins Pin
Sameer Ahmed2-Oct-06 12:08
memberSameer Ahmed2-Oct-06 12:08 
GeneralSound Pin
Tharkunius27-Sep-06 0:38
memberTharkunius27-Sep-06 0:38 
GeneralRe: Sound Pin
Sameer Ahmed2-Oct-06 11:29
memberSameer Ahmed2-Oct-06 11:29 
QuestionUrgent !!! No errors in code but still cant see the video :-( [modified] Pin
~Jabeen~3-Sep-06 22:21
member~Jabeen~3-Sep-06 22:21 
AnswerRe: Urgent !!! No errors in code but still cant see the video :-( Pin
Sameer Ahmed5-Sep-06 2:58
memberSameer Ahmed5-Sep-06 2:58 

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