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Filed under: Distribution •Hardware •Production •

Favorite Technical References

The video industry has saddled us users with some truly ugly numbers to deal with (such as 720x480, 29.97, and so forth) when working with digital video. Making matters worse, these numbers are often misquoted or misunderstood.

Thankfully, there are a few web sites out there with some truly valuable, correct information on digital video standards. Here are the sites we refer to most often when we need to know the inside scoop:

• Chris Pirazzi’s lurkertech site is one of the best repositories of information about how digital video works, including pixel aspect ratios, interlacing, frame rates, and the such.
• A wonderful companion to lurkertech is the IceFloe document Chris Pirazzi wrote for Apple on how to handle digital video inside QuickTime.
• The Advanced Television Standards Committee (ATSC) is the group that unleashed the high-definition digital video standards upon the world. Here is the link for all of their standards. The full high-def spec is described in A/53. To get straight to the meat of the frame rate and frame size issues, download their companion Guide to Use of the ATSC DTV Standard (A/54) and go to page 24, focusing on Tables 5.1 and 5.2 and their surrounding text. (Oh, by the way: Did you catch the comment back on the A/53 page that “the version adopted by the FCC is not necessarily the current version of the Standard”? Gotta love dueling standards committees…)
• I also regularly visit the web site of fellow PVC founder Adam Wilt - it is full of useful information and advice (such as what scroll rates to avoid with text).

When you read these documents in details, you find some interesting facts - facts that you wish all companies in this field were aware of! Such as:

• The real pixel aspect ratio for standard definition NTSC formats such as D1 and DV is 10:11, not 9:10. Too bad virtually all software uses 9:10… As a result, “perfect” circles created inside the computer will be ever so slightly off from perfect circles shot with a camera.
• The real NTSC video frame rate is 30,000/1001 instead of 29.97 (2997/100). You guessed it: Most software actually uses 29.97. If you feed a video capture that is properly tagged as 30,000/1001 into one of these systems, you may eventually get a repeated frame - in some cases, the very first frame! Realted to this, a common cure for voodoo inside After Effects is to explicitly conform all supposedly “29.97” sources to exactly 29.97 fps in the Interpret Footage dialog; this fixes a lot of mysterious clip duration and speed problems:
  

They say knowledge is power…although to be honest, when confronted with all of this information, sometimes I wonder if ignorance is indeed bliss (at least in the short term).

But ultimately, knowing how everything actually works means you can solve your problems and get back to being creative, rather than wondering what voodoo technical curse is going to haunt you next!

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