Multimedia video
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By multimedia video I mean the pictures and sounds of a video session. This could be video recorded on a digital camcorder, digital camera or a web camera.
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In multimedia video a camera and microphone capture the pictures and sound in analogue form, these analogue signals are then sent to a video capture adapter board. In order to cut down on the amount of data that has to be processed, only half the number of frames per second that movies use are captured, this is one of the main reasons why multimedia videos may look jerky, the frame rate is much lower than what you are accustomed to seeing.
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The analogue signal enters the video capture adapter board, and is then sent to an analogue to digital converter (ADC), this chip coverts the analogue waves into binary, a string of 1s and 0s. This binary code then passes onto a compression/decompression chip or special software that reduces the amount of data needed to recreate the original video signal. The purpose of this compression is to reduce the file size and complexity, it does this in a number of ways for example if the background of a picture is a single colour, instead of saving the colour information for each pixel of each frame, the compression software saves the data for that colour once; along with the directions for where to use the colour when the video is displayed.
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Compression chips save more space on your hard drive when it writes your video to disk by interweaving the data for the picture with the audio data in a file format called .AVI (audio/video interleave). In order for the video to be played back the .AVI file has to be sent back through a compression/decompression chip or special software in order to restore areas that would have been eliminated by the initial compression. The decompressed .AVI file is then sent in binary form to a digital to analogue convertor (DAC) which translates the binary code back into an analogue wave form that then goes to your speakers and display.
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This process is shown graphically below.
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