[ The PC Guide | Systems and Components Reference Guide | Video Cards | Full-Motion Video ]

Video Decoding Hardware and Software

There are several ways that MPEG (or other video) files can be played on a PC. In every case, the process involves reading the file, decompressing the video data, and then feeding it to the video card for display on the monitor. Since the data is compressed to reduce storage, it must be uncompressed to restore it to a visible image. This takes a great deal of processing power. There are software programs that can be used to decode these files, allowing you to play an MPEG file on your computer. As with every other case where an application takes a lot of processing power, it is more efficient (but more costly) to let dedicated hardware do the function. This is the purpose of an MPEG Decoder.

Much as is the case with 3D accelerators, it is possible to get a dedicated card for MPEG decoding, or to get a regular video card that has an MPEG decoder built into it. Dedicated MPEG decoders come with different capabilities. They often use the video feature connector on the regular video card, to supply video information directly to the card without tying up the system bus with an enormous amount of video data.

Warning: Beware of some video cards that advertise that they "support MPEG decoding" when all they mean is that they will work with a software MPEG decoder. Many of these cards aren't doing hardware decoding at all. They still may provide acceptable performance, but make sure you know what you are buying.

The quality of MPEG decoders varies, with generally the more expensive ones providing better quality. A high-quality decoder will allow the display of full-screen, smooth video animation while leaving the system CPU free to do other tasks. A cheaper hardware decoding solution, or a software package, may have problems keeping the supply of data to the video card which can result in choppy performance or lost frames. In some cases, this is compensated for by running the video in a small window instead of full-screen, and in others by slowing the frame rate down to less than 30 frames per second. Others reduce the resolution of the screen.

Video encoding and decoding software and hardware is still evolving today and is likely to improve dramatically in coming years. By the end of the decade it is likely that a PC without smooth video capability will be as out of place as one without graphical abilities is today. However at present video on the PC still does not provide very good images compared to a regular VCR and TV combination, unless you are using high-end hardware.

Next: TV Tuners

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