Loading a Project File

Microsoft DirectShow 9.0

Loading a Project File

To load a project file, you need two components: the XML parser and an empty timeline. The XML parser reads an XML project file and creates each object defined in the file. Then it inserts the objects into the timeline and sets any timeline attributes, such as the default frame rate. The following code example loads a file.

HRESULT         hr;
IAMTimeline     *pTL = NULL;
IXml2Dex        *pXML = NULL; 
hr = CoCreateInstance(CLSID_AMTimeline, NULL, CLSCTX_INPROC_SERVER, 
            IID_IAMTimeline, (void**)&pTL);
hr = CoCreateInstance(CLSID_Xml2Dex, NULL, CLSCTX_INPROC_SERVER, 
            IID_IXml2Dex, (void**)&pXML);
BSTR bstrFile = SysAllocStringLen(OLESTR("C:\\example.xtl"), 15);
hr = pXML->ReadXMLFile(pTL, bstrFile); 
SysFreeString(bstrFile);
pXML->Release();

The parser exposes the IXml2Dex interface, which contains methods for loading and saving project files. The timeline exposes the IAMTimeline interface, which contains methods for manipulating the timeline and creating new timeline objects. Call the CoCreateInstance function to create each component, as shown. Remember that by creating a new instance, you are incrementing the reference count on the interface. To avoid memory leaks, always release an interface when you are through with it. In this example, the pointer to IXml2Dex is not needed for anything more, so you can release the interface. The pointer to IAMTimeline is still needed for previewing the timeline.

The IXml2Dex::ReadXMLFile method reads the specified file and populates the timeline with the objects defined in the file. The file name is specified using a BSTR value. To shorten the example, the file name in the example is given as a literal string. Normally, you obtain it from an Open File dialog or something similar.

If the ReadXML method is successful, it returns a success code. Otherwise, it returns an error code such as VFW_E_INVALID_FILE_FORMAT. Always check the return value, in order to handle error conditions gracefully. Again for brevity, the example code does not check for errors.