Games - DirectShow

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DirectShow (sometimes abbreviated as DS or DShow), codename Quartz, is an application programming interface produced by Microsoft for software developers to perform various operations with media files. It is a replacement for Microsoft's earlier Video for Windows technology. Based on the Microsoft Windows Component Object Model framework, DirectShow provides a common interface for media across many of Microsoft's Programming Languages, and is an extensible, filter-based framework that can render or record media files on demand at the behest of the user or developer. The DirectShow development tools and documentation are distributed as part of the Microsoft Platform SDK.

Applications such as Windows Media Player use DirectShow or a variation thereof to display content from a file or URL. DirectShow's most notable competition is Apple Computer's QuickTime framework.

History

ActiveMovie, codename Quartz, the predecessor of DirectShow, was started in the Windows 3.0 days by Geraint Davies for Microsoft as an answer to QuickTime, the most popular media platform at the time. ActiveMovie was first available as an add-on to Windows 95 and that required Internet Explorer 3.0. Mostly its only purpose at the time was to serve as a plugin for Internet Explorer to play media files inside of its window(s), such as what QuickTime offered for Netscape and Internet Explorer at the time, and to serve as a replacement for Video for Windows, particularly for MPEG files whose frame-reordering was difficult to deal with in Video for Windows.

In 1998, around the time of DirectX 5's release, ActiveMovie was renamed to DirectShow (reflecting Microsoft's efforts at the time to consolidate technologies that worked "directly" with hardware under a common naming scheme) and was included part of the "DirectMedia SDK". In version 7 of DirectX, DirectShow became part of the mainline distribution of the DirectX SDK and given its own place alongside other DirectX APIs such as DirectInput. Even then, DirectShow was mostly used as a way to receive data from video input devices, such as a camcorder, and the ability of it to render data from a file was mostly used by Windows Media Player.

As of April 2005, DirectShow was removed from DirectX and moved to the Microsoft Platform SDK instead. The DirectX SDK is, however, still required to build DirectShow samples .

Design Model

The way DirectShow works usually is that a developer creates a filter graph, adds some filters – possibly custom – to the graph, and then renders a file, URL or camera. During the rendering process, the filter graph searches the Windows Registry for registered filters and builds its graph of filters based on the location provided. After this, it connects the filters together, and, at the developer's request, plays/pauses etc. the created graph.

Each filter represents a stage in the processing of the data, e.g. reading from a file or camera, decoding, transforming or rendering. The filter has a number of pins that represent connection points on the filter that can be connected to other filters. Pins can be either output or input. Depending on the filter, data is either "pulled" from an output pin or "pushed" to an input pin in order to transfer data between filters.

Most filters are built using a set of C++ classes provided in the DirectShow SDK, called the DirectShow Base Classes. These handle much of the creation, registration and connection logic for the filter. For the filter graph to use filters automatically, they need to be registered in a separate DirectShow registry entry as well as being registered with COM. This registration can be managed by the DirectShow Base Classes. However, if the application adds the filters manually, they do not need to be registered at all. Unfortunately, it is difficult to modify a graph that is already running. It's usually easier to stop the graph and create a new graph from scratch.

[ Visit the complete Wikipedia entry for DirectShow ]

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