Improving Indeo® Video Playback Performance With DirectDraw*

Introduction | How DirectDraw Improves Video Playback
Introduction
Indeo® video is Intel's digital video software technology for compressing and playing video on personal desktop computers. The most important factor for smooth playback, even of video files with high frame rates and large windows, is processor speed. Many other variables play a role, however, and another key variable is your graphics card. A graphics card that supports some or all of the features of Microsoft's DirectDraw* architecture can go far towards improving video playback on your PC.
This document explains how DirectDraw architecture helps improve video playback performance.

How DirectDraw Improves Video Playback
When you view a video file on a PC without DirectDraw support, the application playing the video (for example, Media Player) sends the data to the operating system's video playback environment, Video for Windows.* Video for Windows in turn sends the data to the Graphics Device Interface, the same interface that draws pixels on the display for nonmultimedia applications such as word processors or spreadsheets. Such applications, however, do not have the same need for speed as a video player does. This is illustrated in Figure 1.
Figure 1. Graphics Applications Without DirectDraw Support

When you view a video file on a PC that has DirectDraw support, the application playing the video (for example, Media Player) sends the data to the operating system's video playback environment, Video for Windows. Video for Windows sends the data to DirectVideo*, which in turn sends it to DirectDraw for manipulation, bypassing the relatively slow Graphics Device Interface. DirectDraw communicates with your graphics card by means of its device drivers, and the graphics card writes the video image to your display. This is illustrated in Figure 2.
Figure 2. Graphics Applications With DirectDraw Support

DirectVideo
As you can see from Figure 2, when you run Video for Windows under Windows 95, DirectVideo is required to connect to DirectDraw. Ordinarily, this connection is made without any action necessary on your part. However, if you are manipulating the drivers for your graphics card (for example, downloading updated ones), you must ensure that the manufacturer also provides the DirectVideo driver dvideo.dll if that graphics card supports DirectDraw.
ActiveMovie*
When Microsoft ships ActiveMovie, it will replace both Video for Windows and DirectVideo, as illustrated in Figure 3.
Figure 3. Graphics Applications With ActiveMovie

How Your Operating System Plays Video Files
PCs that use operating system software only to play video do so as follows:

The application sends one frame of the video file to the Indeo video codec.
The video frame is held in system memory, where the Indeo video codec uses the Pentium® processor to decompress it. The amount of data grows.
The processor next converts the color information from the compact form used by the codec to the RGB form required by the PC monitor. The amount of data grows again.
If you ask the application to double the window size, the processor performs the calculations necessary to do so. The amount of data grows yet larger.
The resulting large amount of data is sent over the bus to the graphics hardware responsible for writing to the display.

This process is illustrated in Figure 4.
Figure 4. Software-only Video Playback

If your graphics card can take advantage of some or all of the capabilities afforded by DirectDraw, however, the process is instead as follows:

The application sends one frame of the video file to the Indeo video codec.
The codec decompresses the frame in system memory.
This relatively small amount of decompressed data is sent over the bus to the memory on the graphics card, transparently to the application.
Special, optimized code running on the graphics card converts the color information.
If you ask the application to double the window size, special, optimized code running on the graphics card does so.
The data is written to the display.

This process is faster in three ways:

Much less data is sent over the bus, decreasing the time needed to transfer it.
Color conversion runs faster because the code on the graphics card is especially optimized for the operation.
Enlarging the window is also faster for the same reason.

Depending on the details of color conversion and video content, the image quality may also improve.
The hardware-assisted process is illustrated in Figure 5.
Figure 5. Video Playback Assisted by DirectDraw Software and Graphics Hardware

Where to Get DirectVideo and DirectDraw
Support for DirectVideo and DirectDraw are provided in graphics card drivers. Contact your graphics card manufacturer for more information and the latest software support.