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Defining Profiles in Video by Phil Hippensteel - AvNetwork.com

Defining Profiles in Video by Phil Hippensteel

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Dear Professor Phil,

I hear vendors talking about "high profile" or "main profile" when they are discussing their implementation of video. What is a profile?

Rose, Columbus, OH


Rose,

Profiles in video serve essentially the same purpose as they serve in more general discussions of computer accounts, systems, and configurations. They are groups of attributes, settings or choices to be determined. For example, in MPEG-2 there are six profiles: Simple, Main, 4:2:2, SNR, Spatial and High. Simple profile supports only 4:2:0 format, 720X576 resolution, and no B frames. When a codec is configured, the software will allow the user to simply check a box next to Simple, rather than confront the user with three choices that might make the task seem more complex.

If a user picks Main profile in MEG-2, they will also be forced to pick a Level: Low, Main, High 1440 or High. Since most codecs use only Simple or Main profile, the set of sample methods, resolution and GOP (group of picture format) could be configured by making no more than two choices.

In H.264 (MPEG-4, Part 10), profiles play a critical role. That’s because there are many more choices to make in defining a complete compression method. As an example, if a user chooses Simple profile, there are four levels. If the user picks level 3, they have chosen 352X288 resolution, 128 kbps maximum bit rate and a maximum of four objects. H.264 allows compression of objects within frames rather than only compression of the entire frame.

Phil Hippensteel, Ph.D., is a professor of information systems at Penn State Harrisburg. Send your questions to Professor Phil via AVTIntern@nbmedia.com.

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