Aspect Ratios and Resolutions Explained
This article is primarily geared towards users of the PAL system (used in the UK), so if you live in the USA, the resolutions for you may vary, but the same general information will still apply.
N.B. Picture Aspect Ratios are written in this format: Horizontal : Vertical
Televisions are currently made with two picture aspect ratios: 4:3, and 16:9 (widescreen). Now lets take a look at the resolutions used by DVD-Videos, VideoCDs, and SVCDs:
DVD-Video: 720x576 / 704x576 / 352x576 / 352x288
VideoCD: 352x288
SVCD: 480x576 / 352x576
You’re probably now sitting there thinking “But how can that possibly be right? My SVCDs would be squashed up horizontally if those resolutions were correct, yet they appear in their correct shape on my TV!” Well the answer is this:
All of these media are encoded in MPEG1 or MPEG2 format. All MPEG files carry a piece of information called a DAR (Display Aspect Ratio) Flag, which states the aspect ratio the video should be played back at (either 4:3 or 16:9). DVD players and good software MPEG players (such as Cyberlink’s PowerDVD and InterActual Player) read these DAR Flags, and resize the video to fit the stated aspect ratio. So a movie with a resolution 720x576, carrying a DAR Flag of 16:9, will be resized to 1024x576 on playback (1024:576 cancels down to 16:9) and would fill a 16:9 television correctly. If it’s DAR Flag was 4:3, however, the video would be resized to 768x576 (768:576 cancels down to 4:3) and fill the 4:3 television.
If you play your MPEG file in Windows Media Player, however, you’ll probably find your movies look squished. This is because WMP currently ignores DAR Flags altogether. Hopefully Microsoft will add DAR Flag-reading functionality to their player soon.
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