Introduction to DirectShow Editing Services

Microsoft® DirectShow® Editing Services (DES) is an application programming interface (API) that greatly simplifies the tasks involved in video editing. DES is built on top of the core DirectShow architecture. It abstracts much of the complexity of DirectShow, and provides a set of interfaces designed specifically for manipulating video editing projects. As an application developer, you get the benefits of DirectShow inside a framework much better suited for creating video editing applications.

The core of DirectShow is a powerful architecture for handling streaming media. An application can use it to play multimedia content authored in a wide variety of formats, without the developer needing to worry about file compression and other tedious details. Prior to DES, however, DirectShow lacked the flexibility needed for nonlinear editing.

For example, suppose you wanted to create a video sequence consisting of 4 seconds from source A, followed by 10 seconds from source B, and ending with 5 seconds from source C. You could accomplish that much fairly easily using only the core DirectShow API.

But what if you decided that source C should come before source B, not after; that the sequence should use 8 seconds from source A, not 4; and that the entire production needed a separate audio track playing in the background? Even minor changes such as these could be difficult to implement. But the scenario just described is a trivial editing project in DES—you can do it with a handful of method calls.

Here are some of the features that DES brings to DirectShow:

• A timeline model that organizes video and audio tracks into nested layers, making it easy to manipulate the final production
• The ability to preview a video project on the fly
• Project persistence through an XML-based format
• Support for video and audio effects, as well as transitions between video tracks (such as fades and wipes)
• Almost 100 standard wipes, as defined by the Society of Motion Picture and Television Engineers (SMPTE)
• Keying based on hue, luminance, RGB value, or alpha value
• Automatic conversion of frame rates and audio sampling rates, enabling a production to use heterogeneous sources
• Resizing or cropping of video

The quickest way to see DES in action is to run the sample application XTLTest Sample. This utility parses DES project files (authored in XML) and renders them to the screen. You can experiment with XtlTest by manually editing sample project files and then rendering them to see the change.