Video Capture, Transcoding, and Authoring/Terminology

This is a glossary covering terms commonly encountered when dealing with the subject of this book. More detail can be found in the book, Wikipedia, and in other sources.

Glossary

 * Deinterlacing — the process of converting interlaced video into a progressive equivalent. Deinterlacing takes two forms: the conversion of video that was created in interlaced form from interlaced to progressive (e.g., true interlaced video as created by a video camera), and inverse telecine, which is the recovery of the original progressive film frames from interlaced telecine video. Inverse telecine is a relatively simple process. Deinterlacing true interlaced video is inexact and difficult.


 * (Video) Field — a division of a frame obtained by sampling only a portion of the scan lines in that frame. Where fields are used in modern video, they are obtained by sampling every other line from a frame; thus two fields, one containing the even scan lines and the other the odd, make up a frame of video. The fields are said to be "interlaced" and are transmitted consecutively.


 * (Video) Frame — the basic unit of video transmission, a single complete image. A frame may be composed of multiple interlaced fields, or may be a single progressive unit. A frame is made up of a stack of horizontal scan lines; this is a product of the scan line-oriented nature of analog video. In digital video, there is less of a distinction between horizontal and vertical rows of pixels.


 * Frame Rate, frames per second, fps — the rate at which frames occur in a video stream. Some common frame rates are 29.97 fps (NTSC), 24 fps (film), 23.976 fps (film playback rate for NTSC), and 25 fps (PAL).


 * Hard Telecine — recorded interlaced material derived from film so that the telecine interlacing is built into the signal. An NTSC hard telecine recording has interlaced frames at 29.97 fps. This is different than what normally occurs with film sources on DVDs, where the content is stored as a 23.976 fps progressive stream that is then converted (by a 3:2 pulldown converter in the DVD player) to an interlaced stream at 29.97 fps for viewing.


 * Interlacing, interlaced scan — made up of a sequence of fields that in turn make up a sequence of frames. NTSC is interlaced; an NTSC frame consists of an even field (the even numbered scan lines from the frame) followed by an odd field (the odd numbered scan lines).


 * Inverse telecine, IVTC — the process of converting telecined video back into its film equivalent. Generally, this involves deinterlacing as well as a change in frame rate. It is a (somewhat) straightforward process.


 * Progressive, progressive scan — made up of a sequence of progressively-scanned (i.e., non-interlaced) frames. A progressive scan frame is an entire frame; it is called progressive because the frame appears in the video stream in its entirety one line at a time from top to bottom.


 * 3:2 Pulldown — a process used to convert 24 fps film source into 29.97 fps interlaced NTSC video. Because four 24 fps film frames will fit evenly (practically speaking) in the space of five 29.97 fps NTSC frames, four film frames are fit into five video frames by interlacing two of the four film frames so that three of the video frames are a mixture of two of the film frames; the other two film frames appear intact. This produces a relatively smooth conversion.


 * Pullup - synonym for inverse telecine.


 * Scan line — a horizontal line in a video frame or field. Analog television physically draws video images from the top to the bottom of the television screen, one horizontal line at a time. Digital monitors work, at least conceptually, the same way. NTSC video has approximately 480 visible scan lines; PAL has 576.


 * Telecine — the process of converting film shot at 24 frames per second into video at either 29.97 fps (NTSC) or 25 fps (PAL).

Contributors
Joseph N. Hall