Saturday, April 3, 2010

directshow debugging tips

1. View graph
When we render a media file, directshow uses intelligent connect to build a working graph for us. It may add some filters implicitly if necessary. From my perspective, it all happens transparently. It's user friendly and powerful. But while debugging, we need to know exactly how is the graph constructed and connected, at runtime. Directshow provided a utility method AddGraphToRot in %WINSDK%\Samples\multimedia\directshow\common\dshowutil.h. We can use it to register our graph to running object table, and then view the graph in graphedit. After the graph has been registered, we select File - Connect to Remote Graph in graphedit to bring up remote filter graph list. Then select the registered graph to view.

2. Keep log
IGraphBuilder exposes a SetLogFile method that can be used to specify a log file. Once set, all of the graph's activities will be saved to the log file, including how filter's are connected, how the graph attempted to connect pins. These information are valuable for debugging filters.
pGraph->SetLogFile((DWORD_PTR)CreateFile(TEXT("C:\\graph_builder.log"), GENERIC_WRITE, 0, NULL, CREATE_NEW, FILE_ATTRIBUTE_NORMAL, NULL));

3. Dump graph
In the log file generated by graph, components (filter and pin) are identified with their address in memory. The friendly name of the component isn't shown which make the log file harder to understand by human. Here is a small utility function that dumps all filters and their pins with corresponding memory address and name, in the format shown below.

1 comment:

Sachin said...


All 4 are valuable. I am just beginning Directshow programming and this is a great help.