A Modular and Extensible Architecture

Because the digital home PC is a relatively new platform category, it will inevitably continue to evolve rapidly for some time. Thus, a useful evaluation tool must be designed to evolve as well. To provide that flexibility, the team adopted an architectural framework that is both modular and extensible.

The team also decided that the new tool would evaluate subject platforms by executing a complete range of typical user tasks. An initial group of use cases was selected, drawn from user applications recognized by the Digital Living Network Alliance* (DLNA). Each selected task was then broken down into its basic functional units and organized into a hierarchy of increasing difficulty. The team devised a structural model of user tasks composed of three elements: primitives, scenarios and usage groups.

• Primitives are the basic units of media-handling functionality; single actions performed on a Digital Home platform. Examples include playing back a video, reformatting a video file, recording a TV show, and streaming video. Primitives are sorted into three groups according to the characteristics that will be used for measuring and scoring performance.
• Video quality-based primitives are functions where successful execution is largely determined by the user’s perception of video image quality. The framework for quantitative evaluation of perceived quality is really the core DHCAT innovation, and is described in detail later.
• Response time-based primitives. Speed does matter in some instances, and this group of primitives is evaluated primarily on execution speed.
• Capability check primitives are units of functionality that are scored on a pass/fail basis, depending on whether or not they are supported in a test system. These capability checks will sometimes determine which scenarios a platform can and cannot run.
• A Scenario is a group of up to four typical user primitives that DHCAT runs on each test platform in order to assess media handling performance. They are grouped into three categories.
• Single-primitive scenarios are simple single-function tasks
• Multi-primitive scenarios are more complex tasks that combine two or more primitives for concurrent execution. An example would be playing a video while simultaneously recording a TV show.
• Multi-instantiation primitives can be derived from Single and multi-primitive scenarios. These video-based primitives can be executed with multiple codecs and file formats. “Play video” for instance, might be executed with MPEG*-2, Windows*Media Video*, QuickTime*, or DivX*, depending on which are present on the machine.
• Usage groups are three groups that subdivide the current universe of 25 Digital Home scenarios.
• Usage Group 1 – Basic: Most scenarios in the Basic level specify execution with standard-definition video content.
• Usage Group – HD: Most scenarios in the HD level specify execution with high-definition video content.
• Usage Group – Connected: All scenarios in the Connected level include a video streaming primitive to evaluate the test platform’s ability to deliver content locally.