Video Resolution – Mistakes Were Made

The Most Important Thing

Width and height.  Simple, yet so important.  NTSC, PAL, D1, HD; all defined by resolution.  In pre-web days, or in early web days (anyone else use Mosaic?) it was not much of an issue.  An editor brought the video in, edited it and laid it back to tape  (on a side note, does anyone want to buy a Sony BVH-2000 cheap?).  Our editor may know that the video is 720×480 or he may not.  Since it’s always the same resolution throughout the process, it doesn’t really matter to him.

Skip ahead to web video.  Now the video needs a smaller resolution and our editor has a lot to learn.  CIF, QCIF, 320×240 or 128×96(!).  Most of them never did learn, and most people dealing with video still don’t have a grip on the concept.

Video Is Not 720 Pixels Wide

  • The largest online retailer in the world recently sent me specs for placing video on their site. They suggested a width of 720 pixels.  They got it wrong.
  • A major film studio recently contacted me, asking why a trailer was “squished.”  A designer had encoded the video to 720×270.  He got it wrong.

There’s one thing that you should know.  Standard Definition Video, in the real world, is not 720 pixels wide.  If you are about to put video on your site at 720×480 or 720×360, stop now.  Yes, D1 NTSC resolution is 720×480 on the tape and in your editing system and on your DVD, but…it is meant to be played back at 640×480.  This is the standard 4:3 resolution of your analog television set.  If the video is letterboxed to 16:9, it should be played back at 640×360.

*There is only one NTSC exception to this:  anamorphic video.  In most cases this will be a 16:9 video fitting the entire 720×480 frame.  Anamorphic video of this sort can be resized to to 720×404 or played back at 852×480.

In the first case above, they assumed that 720 was the standard width of video.  They did not realize that most video will have to be stretched in some direction to meet their specs.  720×480 would be stretched to 720×540.  720×360 (after stripping out the letterboxing) would be stretched to 720×404.

In the second case, the designer simply took a 720×480 trailer, stripped out the 2.35 Widescreen letterboxing and encoded.  The files looked fine at 640×270.

Video Resolutions Are Always Even (at least)

Video compression works geometrically.  The early codecs, MPEG-1 and MPEG-2 worked on a 16×16 basis.  The best resolutions used a width and height divisible by 16.  720×480, 320×240, 512×384 and etc.  Later, usable resolutions expanded to include resolutions divisible by eight and four.

Today, one can only ask for even.

  • I was recently asked by a major online site for FLVs at 400×277 and 130×89.  They got it wrong.
  • The major media company in the world asks for FLV at 364×205.  They got it wrong.

How did they get it wrong.  They may have understood that video should be 4:3 or 16:9 or 2.35:1.  They then chose their width and tried to figure out the correct height.  In the second case, that would be 364*9/16=204.75.  Their mistake was rounding up to an odd integer.  The correct move would be to round down to 204, conveniently divisible by 4.

In the first case, they are all over the map.  400 width in a 16:9 should have gotten them 400×225, easily rounded down to 224 (beautifully divisible by 16).

Wrapping Up

Hopefully this information will be helpful for Designers and Execs trying to make decisions about their online video.  Summing up:

  • The largest 4:3 online resolution available from NTSC is 640×480.  The largest 16:9 resolution available from letterboxed NTSC is 640×360.  Anything larger is a stretch (literally).
  • All online video resolutions should be (at a minimum) even in width and height.  Divisible by 4, 8 or 16 is better and better.

I am available for consultation on these issues:

wcaulfield@metroencoding.com

No charge to clients of Metro Encoding.

Published by

William

Know lots of stuff about (mostly) meaningless things.

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