Recall that for historical reasons NTSC uses a frame rate of $29.97 \mathrm{fps}$.
But usually we capture video at 30 (or sometimes just 15) fps. To make these values jibe, a "drop frame" format is used. Naturally, however, one does not like to physically drop actual frames, so instead a few time codes are dropped per several minutes: we skip one time code assigned to frames every so often.
Devise a scheme for doing this so that we end up dropping an integer number of time codes per an integer number of minutes.

Question

Recall that for historical reasons NTSC uses a frame rate of $29.97 \mathrm{fps}$. 
But usually we capture video at 30 (or sometimes just 15) fps. To make these values jibe, a "drop frame" format is used. Naturally, however, one does not like to physically drop actual frames, so instead a few time codes are dropped per several minutes: we skip one time code assigned to frames every so often. 
Devise a scheme for doing this so that we end up dropping an integer number of time codes per an integer number of minutes.

Quizplus · Accepted Answer

The Answer is In 5 minutes, use not

5 * 60 * 30=9000

, but just

5 * 60 * 29.97=8991=9000-9

frames. This is sometimes phrased in terms of

10 \mathrm{~min}

: in 10 minutes, use not

10 * 60 * 30=18000

, but just

10 * 60 * 29.97=17982=18000

18 frames.

Recall That for Historical Reasons NTSC Uses a Frame Rate 29.97fps29.97 \mathrm{fps}29.97fps

Recall That for Historical Reasons NTSC Uses a Frame Rate $29.97 \mathrm{fps}$