PRB: Poor Performance When You Preview Video

When you preview video on a Windows 2000 or Windows XP-based portable computer, the video may play slower than the video camera's capabilities. Additionally, the preview video may be garbled, jerky, or inconsistent in its motion.

This behavior may occur because of power-management features in the portable-computer processor. Other system activity may also affect video playback. Problems with streaming-video programs may occur when you run a mobile processor in a reduced-performance mode, when the processor performance mode changes dynamically, or when you switch your system power source from alternating current (AC) to battery power. If you run a processor in a low-performance mode, this may not provide enough processing power to properly render a video stream. If processor performance modes change dynamically, this may interfere with video playback.

To resolve this issue, use the following guidelines. These guidelines apply only to portable computers that use processor power management technologies, such as Intel SpeedStep technology, AMD PowerNow! technology, or other similar technologies that can change the processor speed.

When video or audio playback is in progress, do not switch the portable computer from AC power to battery power.

Windows 2000
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Use the applet or configuration utility provided by your system vendor to select a setting that does not allow the processor speed to change. If video playback performance is compromised by running a processor at a low speed, select the highest speed available. See your system manufacturer's documentation for details about changing these settings.

Windows XP
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Set the power scheme to Always On. To do this, follow these steps:

1. Open Control Panel, and then click Power Options.
2. Click the Power Schemes tab.
3. Under Power Schemes, click Always On.

As described in the "More Information" section of this article, the Always On power scheme runs the CPU in its highest performance state. After your computer is set to Always On, try previewing the video again to see if performance improves.

NOTE: If you use the Always On power scheme on a portable computer, this may greatly reduce battery life and cause the computer to run too warm. Be sure to select a more appropriate power scheme, such as Portable/Laptop or Max Battery, for standard use and when you run a portable computer on battery power.

Modern portable computers use processor performance state technologies, such as Intel SpeedStep Technology, AMD PowerNow! Technology, and others. These technologies offer greatly increased portable computer battery life without sacrificing CPU performance. To reduce processor power consumption, these technologies permit the processor to run at reduced core voltages and clock frequencies, referred to collectively as performance states. When you change the processor performance state, access to system memory is temporarily blocked. As a result, streaming devices dependent on accessing memory may be starved for data, resulting in glitches or drop-outs in playback. Additionally, running a processor in a low-performance mode may not provide enough processing power to properly render a video stream.

On a Windows 2000-based computer, processor performance states are controlled by the system BIOS. Frequently, an applet or configuration utility may be provided by the system vendor to allow the user to set processor performance options. Typically, these applets allow the user to set the processor to run according to the following options:

• At the highest state for best performance
• At the lowest state for best battery life
• Automatic, which dynamically changes the performance state based on CPU usage

On a Windows XP-based computer, control of processor performance states is inherent. Four modes of operation, known as processor policies, are used to control processor performance states. The processor policies used by Windows XP are: These processor policies are directly tied to the power schemes available in the Power Options tool in Control Panel. The following power schemes are provided with Windows XP. Note that additional power schemes may be provided by your system vendor.

Processor Policy
================ The third-party products that are discussed in this article are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.

Note If you use Windows Vista, you can visit the following Microsoft Web page for help with power consumption and battery life problems: