Digital video is among the most powerful tools available to the multimedia developer. Reading a story about a news article cannot compare with watching and listening to a video clip of the disaster unfolding. Of all the multimedia elements we have looked at so far, video places the greatest demand on the computer hardware. Video plays at either 25 or 30 frames per second. One coloured frame, as we saw earlier, can take up as much memory as 1 megabyte, meaning you need 30 megabytes per second, 1.8 gigabytes per minute or 108 gigabytes per hour. This needs a vast amount of storage and an incredibly fast computer to be able to process this amount of data. Video Hardware To capture digital video, requires additional hardware to be added to your computer system. Video Capture Board Video is normally captured from a video camera or player. The computer itself cannot process this information therefore a video capture board is inserted into the computer. The video capture board takes the analogue video image and converts it to digital video that the computer can process. This is extremely time consuming and frequently frames will be missed so the resulting digital video will appear ‘jerky’. The number of frames per second that can be captured depends upon the size of the image being captured, the colour depth and the quality of the video capture board. Video Compression Board With storage of 30 megabytes per second, compressing the data is a must. The most common compression for moving images is Moving Picture Experts Group (MPEG). MPEG compresses the data to about two percent of its size without the picture becoming significantly poorer. This not only allows the video to be stored in a smaller hard disc, but also allows the data to be transferred from backing storage to the computer quickly enough. Video Playback Boards If you do not have a separate video playback board, then the computer’s CPU will have to carry out all the processing and this will give slow and poor quality video playback. Having a separate video playback board allows the CPU to get on with other tasks, while the video playback board processes the video data and displays it on the monitor. This greatly speeds up and improves the quality of the video playback. Nowadays, a single video card generally replaces these three boards. For example video cards can capture full screen video at up to 30 frames per second, compress the data using motion JPEG to 3% of its original size, and output to the monitor, television or video cassette recorder.
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