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Terminology Description

Constant Bit Rate - is a mode for encoding audio or video in which the bitrate for each frame or unit is restricted to remain constant.  Bitrate has a direct correlation to file size and quality. The higher the bitrate the better the quality (and the larger the file size). Variable bitrate (VBR) provides an alternative that allows for efficient monitoring of audio or video complexity in able to increase or decrease bitrate accordingly. The result is a lower bitrate for simple scenes, a higher bitrate for more complex visual scenes and, ultimately, yielding a better overall rendering in a smaller or the same file size.


Single channel recording is known as mono  recording. Stereo recording involves the recording of 2 channels (left and right). In interviewing situations, the two channels associated with stereo recording allow the separation and isolation of channels for the interviewer and the interviewee. Stereo recording is ideal from a sound quality situation involving two microphones and two entities. Single-point stereo microphones involve the left-right separation but do so from a single source, yielding much less sound isolation. Stereo recording doubles the data footprint of your recording. Some recorders are capable of using a stereo microphone setup but recording in mono. The recorder “mixes” the two channels together. The resulting file is half the file size of a stereo recording, but the channel isolation will be lessened. Some portable recorders will not allow you to record mono files. Digital video can also capture either stereo or multiple channels of audio.

Chroma Key Compositing

Technique of combining and replacing multiple layers of video. Commonly referred to as “green screening,” capturing a video with a green screen background enables an editor or producer to “replace” the background with an image and leave the foreground intact. This allows a video production to customize the backgrounds. This is very difficult to do for oral history as it requires a great deal of computing power and oral history interviews in their raw form are long, large digital video files. This is usually associated with production phases of disseminating video.


Software solution that compresses and decompresses an audio or video file for digital playback. Often proprietary, the goal of a particular codec is to compress a recording in order to make the file size smaller while simultaneously retaining as much quality as possible. An “efficient codec” is a codec that excels at lowering file sizes and minimizing perceived loss of information. Codecs are not file formats. Usually a codec such as H.264 for video is delivered in a container format such as a .mov.