Video Formats Choosing

Digital video can have a dramatic impact upon the user. It can reflect information that is difficult to describe in words alone, and can be used within an interactive learning process. This document contains guidelines to best practice when manipulating video. When considering the recording of digital video, the digitiser should be aware of the influence of file format, bit-depth, bit-rate and frame size upon the quality of the resulting video.

Digital video consists of a series of images played in rapid succession to create the illusion of movement. It is commonly accompanied by an audio track. Unlike graphics and sound that are relatively small in size, video data can be hundreds of megabytes, or even gigabytes, in size.

The visual and audio information are individually stored within a digital 'wrapper' an umbrella structure consisting of the video and audio data, as well as information to playback and resynchronise the data.

The provision of video data for an Internet-based audience places specific restrictions upon the content. Quality of the video output is dependent upon three factors:

• Frame size - the height and width of the video window according to the number of pixels. Higher resolutions produce an equivalent increase in file size and require a greater amount of bandwidth to download.
• Frame rate - The number of frames per second. Video encoded at a low frame rate (particularly below 15 frames per second) will appear jerky and unprofessional to the eye.
• Bit Depth - determines the number of colours that will be used to view the movie. The balance between image quality and file size should be considered.

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