Inserting a DMO in the DirectShow Filter Graph

DirectX Media Objects (DMO) can be thought as light weight DirectShow filter with limited functionality, But are easier to develop, mostly used for audio video effects.

DMOs can be inserted in a filter graph through a wrapper filter, after DMOs insertion in the filter graph it is treated like a normal filter.

A DMO is a COM object. So wrapping means it is aggregated by the DMO Wrapper Filter.

DMO creation sequence is,

1. Call CoCreateInstance to create DMO Wrapper Filter.
2. Query the DMO Wrapper Filter for the IDMOWrapperFilter interface.
3. Initialize the required DMO with IDMOWrapperFilter::Init.

// Create the DMO Wrapper filter.
IBaseFilter *pFilter;
HRESULT hr = CoCreateInstance(CLSID_DMOWrapperFilter, NULL,
    CLSCTX_INPROC_SERVER, IID_IBaseFilter, (void**)&pFilter);

if (SUCCEEDED(hr))
{
    // Query for IDMOWrapperFilter.
    IDMOWrapperFilter *pDmoWrapper;
    hr = pFilter->QueryInterface(IID_IDMOWrapperFilter,
                                                (void**)&pDmoWrapper);

    if (SUCCEEDED(hr))
    {
        // Initialize the filter.
        hr = pDmoWrapper->Init(CLSID_MyDMO, DMOCATEGORY_VIDEO_EFFECT);
        pDmoWrapper->Release();

        if (SUCCEEDED(hr))
        {
            // Add the filter to the graph.
            hr = pGraph->AddFilter(pFilter, L"My DMO");
        }
    }
    pFilter->Release();
}

Inserting DMO in filter graph through System Device Enumerator

The other way to add a DMO in the filter graph is through System Device Enumerator. The System Device Enumerator can be used to enumerate the DMOs in various categories, and through System Device Enumerator it is easy to instantiate a DMO through IMoniker::BindToObject which automatically creates the DMO Wrapper filter and initializes it with the DMO.

Enumerating Filters in the Filter Graph

I have posted earlier about enumerating the DirectShow filters registered on a client computer.

And another post a enumerating the Pins a DirectShow Filter have.

But this time I am posting about enumerating the DirectShow filters in a specific Filter Graph. A DirectShow filter graph can be created in a number of ways, the easiest is through intelligent connect way, just call IGraphBuilder::RenderFile on a media file and all the graph will be built for you.

Now after the filter graph built it is not known which filters are inserted in the filter graph by the Filter Graph Manager, the filters in a filter graph can be easily seen through the GraphEdit if you register the filter graph in the Running Object Table (ROT). At the time let us explore the filter graph through the code.

HRESULT EnumFilters (IFilterGraph *pGraph)
{
    IEnumFilters *pEnum = NULL;
    IBaseFilter *pFilter;
    ULONG cFetched;

    HRESULT hr = pGraph->EnumFilters(&pEnum);
    if (FAILED(hr)) return hr;

    while(pEnum->Next(1, &pFilter, &cFetched) == S_OK)
    {
        FILTER_INFO FilterInfo;
        hr = pFilter->QueryFilterInfo(&FilterInfo);
        if (FAILED(hr))
        {
            MessageBox(NULL, TEXT("Could not get the filter info"),
                TEXT("Error"), MB_OK | MB_ICONERROR);
            continue;  // Maybe the next one will work.
        }

        MessageBox(NULL, FilterInfo.achName, TEXT("Filter Name"), MB_OK);
        // The FILTER_INFO structure holds a pointer to the Filter Graph
        // Manager, with a reference count that must be released.
        if (FilterInfo.pGraph != NULL)
        {
            FilterInfo.pGraph->Release();
        }
        pFilter->Release();
    }

    pEnum->Release();
    return S_OK;
}

 

If you have read few previous posts of this blog then it will not be  difficult to understand the code.

The IFilterGraph::EnumFilters gives us a enumerator which can be used to enumerate all the filters in the filter graph. The IBaseFilter::QueryFilterInfo helps us to know the filter name and wether it is the member of a filter graph or not.

Enum the backbone of DirectShow Graph Building

As a few last post are about enumeration, wether enumerating the Filter Categories or enumerating the filters in those categories or enumerating the filters pins.

Now comes another enumeration related post but this time we will enumerate all the filters in a given graph, this can be useful.

• if you want to find some kind of info about all the filters.
• want to find a specific interface but don’t know which filter implements that interface.
• want to release all the filters in the filter graph.

here is the code about finding info about filter

HRESULT EnumFilters (IFilterGraph *pGraph)
{
    IEnumFilters *pEnum = NULL;
    IBaseFilter *pFilter;
    ULONG cFetched;

    HRESULT hr = pGraph->EnumFilters(&pEnum);
    if (FAILED(hr)) return hr;

    while(pEnum->Next(1, &pFilter, &cFetched) == S_OK)
    {
        FILTER_INFO FilterInfo;
        hr = pFilter->QueryFilterInfo(&FilterInfo);
        if (FAILED(hr))
        {
            MessageBox(NULL, TEXT("Could not get the filter info"),
                TEXT("Error"), MB_OK | MB_ICONERROR);
            continue;  // Maybe the next one will work.
        }

#ifdef UNICODE
        MessageBox(NULL, FilterInfo.achName, TEXT("Filter Name"), MB_OK);
#else
        char szName[MAX_FILTER_NAME];
        int cch = WideCharToMultiByte(CP_ACP, 0, FilterInfo.achName,
            MAX_FILTER_NAME, szName, MAX_FILTER_NAME, 0, 0);
        if (chh > 0)
            MessageBox(NULL, szName, TEXT("Filter Name"), MB_OK);
#endif

        // The FILTER_INFO structure holds a pointer to the Filter Graph
        // Manager, with a reference count that must be released.
        if (FilterInfo.pGraph != NULL)
        {
            FilterInfo.pGraph->Release();
        }
        pFilter->Release();
    }

    pEnum->Release();
    return S_OK;
}

here is the code to find a specific interface on a filter

HRESULT FindFilterInterface(
    IGraphBuilder *pGraph, // Pointer to the Filter Graph Manager.
    REFGUID iid,           // IID of the interface to retrieve.
    void **ppUnk)          // Receives the interface pointer.
{
    if (!pGraph || !ppUnk) return E_POINTER;

    HRESULT hr = E_FAIL;
    IEnumFilters *pEnum = NULL;
    IBaseFilter *pF = NULL;
    if (FAILED(pGraph->EnumFilters(&pEnum)))
    {
        return E_FAIL;
    }
    // Query every filter for the interface.
    while (S_OK == pEnum->Next(1, &pF, 0))
    {
        hr = pF->QueryInterface(iid, ppUnk);
        pF->Release();
        if (SUCCEEDED(hr))
        {
            break;
        }
    }
    pEnum->Release();
    return hr;
}

here is the code which releases all the filters in the DirectShow Filter

Graph

// Stop the graph.
pControl->Stop();

// Enumerate the filters in the graph.
IEnumFilters *pEnum = NULL;
HRESULT hr = pGraph->EnumFilters(&pEnum);
if (SUCCEEDED(hr))
{
    IBaseFilter *pFilter = NULL;
    while (S_OK == pEnum->Next(1, &pFilter, NULL))
     {
         // Remove the filter.
         pGraph->RemoveFilter(pFilter);
         // Reset the enumerator.
         pEnum->Reset();
         pFilter->Release();
    }
    pEnum->Release();
}

Enumerating the DirectShow Filter Pin

When it comes the time of connecting the DirectShow filters manually in DirectShow Filter Graph, at that time we admire the benefits of the Intelligent Connect. To connect a filter manually we have to built the entire filter graph with coding.

First of all a source filer have to be created the filter graph

IGraphBuilder *  pGB;
CoCreateInstance(CLSID_FilterGraph,NULL,
               CLSCTX_INPROC_SERVER,IID_IGraphBuilder,(void**)&pGB);

then a Source Filter have to be added the filter graph, wether with CoCreateInstance() or with System Device Enumerator, All filters can’t be created with CoCreateInstance, Normally the filters which are wrapper to devices have to be created with the System Device Enumerator. But here a source filter is being added that will read the media data from a file from the disk.

IBaseFilter * pSF;
    pGB->AddSourceFilter(L"c:\\media\\video\\ruby.avi", L"Source Filter",

                                                                  &pSF);
    IEnumPins * pEP;
    pSF->EnumPins(&pEP);
    IPin * pOutPin;
    while(pEP->Next(1,&pOutPin,0) == S_OK)
    {
        PIN_DIRECTION pDir;
        pOutPin->QueryDirection(&pDir);
        if(pDir == PINDIR_OUTPUT)
            break;// success
        pOutPin->Release();
    }
    pEP->Release();

Now how to enumerate the pins, IBaseFilter has a method which makes it easy to enumerate the pins a filter have.

HRESULT EnumPins(
  IEnumPins **ppEnum
);

which gives us IEnumPins interface, with this interface you can easily enumerate the pins a filter have wether these are input pins or output pins. you first call Next then check for the pin direction.

HRESULT QueryDirection(
  PIN_DIRECTION *pPinDir
);

For direction checking  QueryDirection is called this method tells us the pin direction.

Now you can call IGraphBuilder::Render to built the entire graph.

HRESULT Render(
  IPin *ppinOut
);
this method takes the output pin to be rendered.

or you can call IGraphBuilder::Connect to directly connect the 

output pin to a downstream filters input pin.

HRESULT Connect(
  IPin *ppinOut,
  IPin *ppinIn
);

Enumerating DirectShow Filters

System Device Enumerator

Wether you locating for a particular filter or want to enumerate all the filters on a system. The System Device Enumerator is a big help. Enumeration of DirectShow filters can be achieved with the help of System Device Enumerator. It is COM object. which expose ICreateDevEnum interface. It means first you have to create the System Device Enumerator object, then you will grab its interface ICreateDevEnum , this interface exposes just one method CreateClassEnumerator this method actually creates  enumerator, which can be used to enumerate the filters in a specific Filter Category, or can be used to enumerate all the Filter Categories on a users system.

Filter Categories

Filter in DirectShow are divided in the categories . Every category has its own class identifier called a CLSID. With the help of this CLSID it is easy to enumerate the filters of that specific class.

But first of all how to enumerate those categories, for this purpose there is a CLSID_ActiveMovieCategories CLSID. With it one can easily enumerate the categories which has filters in them.

HRESULT hr;
    ICreateDevEnum *pSysDevEnum = NULL;
    hr = CoCreateInstance(CLSID_SystemDeviceEnum,

                           NULL, CLSCTX_INPROC_SERVER,
                           IID_ICreateDevEnum, (void **)&pSysDevEnum);
    if (FAILED(hr))
    {
        return hr;
    }
    IEnumMoniker *pEnumCat = NULL;
    hr = pSysDevEnum->CreateClassEnumerator(

                       (GUID)CLSID_ActiveMovieCategories, &pEnumCat, 0);
    if (hr == S_OK)
    {
        // Enumerate the monikers.
        IMoniker *pMoniker = NULL;
        ULONG cFetched;
        while(pEnumCat->Next(1, &pMoniker, &cFetched) == S_OK)
        {
            IPropertyBag *pPropBag;
            hr = pMoniker->BindToStorage(0, 0, IID_IPropertyBag,
                (void **)&pPropBag);
            if (SUCCEEDED(hr))
            {
                VARIANT varName, varCLSID;
                VariantInit(&varName);
                VariantInit(&varCLSID);
                hr = pPropBag->Read(L"FriendlyName", &varName, 0);
                if (SUCCEEDED(hr))
                {
                    hr = pPropBag->Read(L"CLSID", &varCLSID, 0);
                    if (SUCCEEDED(hr))
                    {
                        GUID clsid;
                        if (SUCCEEDED(CLSIDFromString(varCLSID.bstrVal,

                                                               &clsid)))
                        {
                            EnumFilters(clsid, hparent);

 

this snippet of code shows how to enumerate all the filter categories. Now you have all the filter categories it is time to enumerate the filters in those filter categories.

bool CEnumFiltersDlg::EnumFilters(GUID clsid, HTREEITEM hparent)
{
        // Create the System Device Enumerator.
    HRESULT hr;
    ICreateDevEnum *pSysDevEnum = NULL;
    hr = CoCreateInstance(CLSID_SystemDeviceEnum,

                           NULL, CLSCTX_INPROC_SERVER,
                           IID_ICreateDevEnum, (void **)&pSysDevEnum);
    if (FAILED(hr))
    {
        return hr;
    }
    IEnumMoniker *pEnumCat = NULL;
    hr = pSysDevEnum->CreateClassEnumerator((GUID)clsid, &pEnumCat, 0);
    if (hr == S_OK)
    {
        IMoniker *pMoniker = NULL;
        ULONG cFetched;
        while(pEnumCat->Next(1, &pMoniker, &cFetched) == S_OK)
        {
            IPropertyBag *pPropBag;
            hr = pMoniker->BindToStorage(0, 0, IID_IPropertyBag,
                (void **)&pPropBag);
            if (SUCCEEDED(hr))
            {
            // To retrieve the filter's friendly name, do the following:
                VARIANT varName;
                VariantInit(&varName);
                hr = pPropBag->Read(L"FriendlyName", &varName, 0);
                if (SUCCEEDED(hr))
                {
                    // Display the name in your UI somehow.
                    TVINSERTSTRUCT tvInsert;
                    tvInsert.hParent = hparent;
                    tvInsert.hInsertAfter = NULL;
                    tvInsert.item.mask = TVIF_TEXT;
                    CString str(varName.bstrVal);
                    tvInsert.item.pszText = str.GetBuffer();
                    str.ReleaseBuffer();
                    mFiltersTree.InsertItem(&tvInsert);
                }

                VariantClear(&varName);
                pPropBag->Release();
            }
            pMoniker->Release();
        }
        pEnumCat->Release();
    }
    pSysDevEnum->Release();

    mFiltersTree.SortChildren(hparent);
    return true;
}

Here clsid parameter passed is the CLSID of the filter category whom  to enumerate.

NOTE

       this sample don’t enumerate the DMOs on a system as the Graph Edit utility enumerates in its insert filter function. I will try to add it later.

code can be found here

DirectShow which SDK to use ?

The DirectShow was part of the DirectX SDK , then it was removed from the DirectX SDK and was made part of the Platform SDK, But now that Platform SDK has been replaced by Windows SDK. The latest Windows SDK is the Microsoft Windows SDK for Windows Server 2008 and .NET Framework 3.5, released February, 2008.

System Device Enumerator

Another interesting question on tanvon Yahoo Group is,
” Could any one tell me how to go about listing all the DirectShow
Filter Categories so that i can list the filters under each category.”
There are two ways to enumerate the filters the Filter Mapper way and the System Device Enumerator way.
Here I will explain the System Device Enumerator.
The System Device Enumerator is a COM object, which implements the ICreateDevEnum interface,
this intreface exposes only a single method CreateClassEnumerator. This is the method which creates the enumerator object and returns its IEnumMoniker interface, but enumerate what
HRESULT CreateClassEnumerator(
  REFCLSID clsidDeviceClass,
  IEnumMoniker **ppEnumMoniker,
  DWORD dwFlags
);
The first parameter is the class identifier (CLSID) of the device category. these categories are defined in the Dshow.h header file. (e.g. CLSID_LegacyAmFilterCategory , CLSID_AudioRendererCategory ). This is the place to notice that you have to specify which category you want to enumerate.
Once you have the IEnumMoniker, now you can use its methods to easily enumerate the device category. Just call IEnumMoniker::Next  method, this will return an IMoniker interface with this interface you can get the “Friendly Name” of the filter or you can instanciate the filter itself.
For an example see http://msdn.microsoft.com/en-us/library/ms787871(VS.85).aspx

For the URDU version see http://directshow.wordpress.com/2008/08/16/system-device-enumerator/

Intelligent Connect

As a member of yahoo group asked about the so called non-intelligent connect .
Adding and connecting distinct filter in the filter graph manually.
Actually there are many small functions which need to be taken care, So this
may take a little longer to understand, So keep reading this series of blog entries about
connecting filter without intelligent connect in DirectShow.

Intelligent Connect
 There are some intelligent algorithms behind this, Which
share the burden of the programmer. Suppose for a little time what
hassle is hidden behind it. Once the  IGraphBuilder::RenderFile()
is called the Filter Graph Manager searches for the suitable source filter
which can read and understand the format of media file. Then it tries to
search for a filter which can decode or parse that data (this data is called Media Samples in the DirectShow)
which the source filter will handle to it (through transport), The media sample format which is said the Media Type in the DirectShow
must be same that both filters will understand otherwise the connection will fail,
and Filter Graph Manager will drop that filter and will search for another filter which
will handle the samples with the specified Media Type.
Then Filter Graph Manager will try to load other filters to complete the Filter Graph.
At the end it will load the default Renderer to Display the contents on the screen.
and will connect that with the entire filter graph build previously.

DirectShow in Urdu

I am going to keep a new blog DirectShow.WordPress.com . This blog will be and is in Urdu language about definitely DirectShow. I will try to keep my both blogs in synch with each other.

Opening Command Pormpt in the current directory (folder)

This was a big problem for me, as sometimes I have to go in a
folder and afterwords have to open the command prompt in that
same folder.

Now the problem is solved,
1 just make a text file in the current folder
2 and open txt file
3 type in that text file cmd
4 save that file
5 rename it to amazing.bat

every thing is ok , now just click that file
it will open that command prompt in that current folder.

caution never try to name that file to cmd.bat or you
will see an amazing screen
Why if you ask then I will tell, first give some task to
your brain.

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