Introduction
Video playback is one of the most innovative and compelling features of Media Center PCs running Microsoft® Windows® XP Media Center Edition. Quality video playback is essential to sales and widespread adoption of Media Center PCs; reviewers and customers tend to perceive the quality of the overall system on the basis of video playback—if video playback is poor, they tend to perceive the quality of the entire Media Center PC as poor.
Video playback on Media Center PCs is complex and depends heavily on the quality of individual components that are involved in the video playback path. These components include the following:
- TV tuner/capture/compressor device.
- MPEG-2 video decompressor.
- Graphics hardware, including graphics acceleration hardware and the display adapter.
- Display monitors, including CRT/LCD/PDP/DLP computer displays and televisions.
This paper describes the role of each component in video playback, the factors that can contribute to poor video quality, and recommends configurations and tests to obtain the best possible video quality. The paper also lists troubleshooting tips that manufacturers can offer customers who purchase Media Center PCs. This paper is intended to help system manufacturers choose components and adjust settings for the best user experience with video on PCs running Windows XP Media Center Edition. The information in this paper can also be used to guide reviewers and users who are trying to optimize video quality on Media Center PCs.
This paper assumes that readers are familiar with television features of the Media Center user interface in Windows XP Media Center Edition. It also assumes that readers are familiar with the system requirements for Media Center PCs.
System requirements are listed in the Design Guide for Windows XP Media Center Edition. For availability of this document and sources of information about video signals and video processing, see the Resources and Tools section at the end of this paper.
TV/Tuner Capture/Compressor Devise
A TV tuner/capture/compressor device combines the separate video processing stages of tuning, digitization, and compression on a single PCI-compatible add-on board, a USB 2.0, or a 1394 hot-pluggable device. These products are often marketed as personal video recorder (PVR) devices for computers. The PVR device brings compressed broadcast television to the Media Center PC.
TV Tuner
The TV tuner receives a radio frequency (RF) signal from an antenna or cable feed. When the user enters a channel number in the Media Center PC, the TV tuner is the hardware that finds the corresponding RF signal.
Signals appearing as base-band composite video, S-video, or line-level audio from a set-top box, VCR, or DVD player bypass the TV tuner component. Thus, the tuner can be removed from the video processing chain to determine its affect on video quality.
How the TV Tuner Affects Video Quality
Problems with tuning can cause video artifacts, such as ghosting, video snow, and rolling bars or distorted colors. A poor tuner can also lead to corrupted vertical blanking interval (VBI) or closed-caption (CC) data and weak or garbled audio. The most common causes of video artifacts result from the following:
- The user attached the coaxial cable to the wrong connector.
- The tuner has poor sensitivity to attenuated signals.
- The RF signal is weak or scrambled on some channels.
- The TV tuner is set to the wrong input format (antenna/cable or NTSC/PAL).
