29.97/59.94 的由來

Ah, More Math! 29.97 and 59.94!

原則上，NTSC 的圖場率是每秒 1/60 格。（NTSC 為美國（含北美地區）、日本與台灣等地區的電視系統規格；圖場率，就是每秒可以呈現的影像格數）這個數值是根據在北美地區 AC 交流電源的頻率 60Hz 而來的。（台灣地區的交流電源頻率也是 60Hz； 1/50 或是 50Hz 是在 PAL 規格地區所採用的，例如歐洲、中國大陸等地區使用。）不幸的是，當初工程師在制定影像規格時只是針對黑白的影像訊號所設計的，並沒有針對彩色影像來作規劃。所以當彩色電視機出現時，才在訊號上做了一些改變。為了技術原則，調整比原來的格率還要再慢上 0.1% 的速率。這個工作方式超過 29.97fps，直到 59.94fps 的圖場率。

Originally, the field rate of NTSC was 1/60 of a second. This number was chosen to match AC power-line frequencies of 60Hz in North America (1/50 or 50Hz, in PAL). Unfortunately, the engineers who designed the specification did so for a black-and-white video signal, and they did not plan ahead for color. So when color television arrived, they had to make a change in the signal. For technical reasons, this turned out to be a 0.1 percent slowdown in the frame rate. This work out to 29.97fps, leading to a field rate of 59.94fps. (The actual calculation for frames per second is 30x1000/1001, which equals 29.97002997003. For fields, the calculation is 60x1000/1001, which equals 59.940059944006.)

The Article from Final Cut Pro Workflows - The Independent Studio Handbook, Focal Press