Microsoft is the platform of choice for video content playback from both Internet and classic broadcasting channels. In order to cope with the multitude of existing video formats and futures ones Widows applications use the DirectShow framework, a very flexible and extensible framework which enables applications to support any video format providing that necessary third party filters are installed. The filters are basic video processing units, developed by different vendors, which can be linked together to perform certain video processing tasks (capturing, encoding, decoding, editing, rendering).

As the number of filters available on a system increases, the number of filters doing the same task and the number of filters with faulty implementation increases as well. Most DirectShow based applications use automatic filter selection to create a video processing chain composed of unknown filters, also as new filters are installed on the system this chain can change. This is an unacceptable situation when reproducible, reliable results are needed.

VQLab provides the users with the flexibility and extensibility benefits of  the DirectShow framework without compromising reliability, reproducibility and control requirements of a professional test environment. 

Control is provided to the user by allowing him to precisely specify the DirectShow filter chain used for preprocessing the video before the quality assessment. Using our built in graph editor you can select from the abundance of filters installed on your system only the ones that you know are reliable and produce good results. Also the control VQLab gives you over DirectShow allows you to test the quality of the output of different filters, especially encoders and decoders but also resize filters for example.

           
1. VQLab’s built-in DirectShow graph editor. 

The DirectShow graph is saved together with the results if you choose to save them as VQR files, this way you have access to the graph after you’ve computed/saved the results so it’s easy to see in what conditions the results where obtained. 

2. Viewing the text description of the graph in VQLab Results Viewer (a view of the graph similar to the one in picture 1 is also available to see the properties of the filters)  

Reproducibility is made easy by allowing users to save DirectShow graphs and use them later for more video quality testing. DirectShow graphs can be associated with file extensions making sure the same graph is used each time you analyze a certain file type. The graph editor allows you to save a graph to be used later or to be used by VQLab CLI, this means that VQLab CLI offers you the same control over DirectShow as the graphical user interface so you don’t loose control while automating your quality control process.

 
3. Saving a DirectShow graph. 

Due to the nature of DirectShow, installing other filters on your system could change the graph used for preprocessing video files, setting a default graph for an extension avoids this problem ensuring that the same graph is used every time you analyze the same file type. 

The control provided by VQLab ultimately leads to reliability:

• being able to control and reuse the same DirectShow graph ensures reliable quality assessment.
• limiting the use of filters to trusted ones guaranties the quality of the results.
• saving the graph assures you will always know in what conditions the results where obtained. 

VQLab’s unique features combines the flexibility and extensibility of the DirectShow framework with reliability and control requirements of a professional video quality test tool.