Managing Video Editing Projects

The following tips will help you to manage projects in Microsoft® DirectShow® Editing Services.

Changes to the Timeline

• If you change the timeline after you build the filter graph, call IRenderEngine::ConnectFrontEnd again to rebuild the front end. Usually, this does not affect the rest of the graph. Occasionally, however, the render engine needs to delete the entire graph before it rebuilds the front end. (For example, this happens if you add or remove a group.) The ConnectFrontEnd method returns S_WARN_OUTPUTRESET to signal that it deleted the graph. If this happens, your application must rebuild the rendering section of the graph.
• To remove all objects completely from the timeline, call the IAMTimeline::ClearAllGroups method.

Cleanup

• When you are finished using a render engine, call the IRenderEngine::ScrapIt method. As with any COM object, be sure to release every interface pointer when you are finished using it.
• The render engine does not keep a reference count on the timeline. Do not release the timeline before you are done using it, and always call ScrapIt on the render engine first.
• If you release all references to a timeline, do not use any of the objects in that timeline, even if you are holding reference counts on them.

Multiple Timeline Instances

• Do not move timeline objects between timelines. Every object in a timeline must be created by that timeline. The timeline holds an internal cache with information about the objects that it creates; moving timeline objects can disrupt the cache.
• Never use the same instance of a render engine with more than one timeline. The render engine holds a cache with information about the timeline. Multiple timelines will disrupt the cache and cause unpredictable results. If you need two active timelines, make separate instances of render engines for each timeline.
• A timeline can use more than one render engine, but not at the same time. Delete the old render engine before using another render engine. (You would typically do this when you switch from using the basic render engine for preview to the smart render engine for file writing.)

Persistence

• The filter graph is not persistent when you save the project to an XML file. Therefore, you lose any information relating to smart recompression, compression format, or compression parameters. It is up to the application to restore these parameters after it loads a project.