BCD Time format

quantum · 11th September 2003, 21:45

I see times displayed in ifoedit such as 2:06:21.13

Does the last number represent 13/100 of a second? I have never seen a value above 29 for number after the period.

2COOL · 11th September 2003, 22:25

Quote:

Originally posted by quantum
Does the last number represent 13/100 of a second?

That's correct.

mpucoder · 12th September 2003, 02:27

The last number in the timecode is the frame number within that second. For NTSC this is 0 to 29, for PAL 0 to 24.

2COOL · 12th September 2003, 02:33

@mpucoder

I was wondering where you were hiding? I knew you couldn't resist answering a technical question.

quantum · 12th September 2003, 04:43

Quote:

The last number in the timecode is the frame] number within that second. For NTSC this is 0 to 29, for PAL 0 to 24.

Does this mean in addition to the specified time? Example:

0:00:01.15

One second and 15 frames (NTSC).

Does that position it at frame 45?

mpucoder · 12th September 2003, 16:51

Yes, in addition to the time. It is safe to say 00:00:01.15 is 1 second and 15 frames, but not to say 45 frames. The reason for this is that the true frame rate is 29.97 (actually that's approximate, too*) so NTSC uses drop frame timecode. Frame numbers 0 and 1 are dropped whenever needed to adjust the timecode to the actual elapsed time. It is common to drop these frames at the start of every minute not divisible by 10. This gives 18 dropped frame numbers (not frames) every 10 minutes, so that the (29.97 * 10 * 60) 17982 frames are "counted" as 18000.

*Actual NTSC framerate is determined by the color subcarrier frequency (3.579545MHz). Each horizontal line is exactly 227.5 cycles of this frequency, and there are 525 lines per frame. So the framerate is 3579545 / 227.5 / 525 = 29.97002617
That small difference creeps up on timecodes and does result in skipped drop counts.

11th September 2003, 21:45	#1 \| Link
quantum Registered User Join Date: Nov 2002 Location: USA Posts: 528	BCD Time format I see times displayed in ifoedit such as 2:06:21.13 Does the last number represent 13/100 of a second? I have never seen a value above 29 for number after the period.

12th September 2003, 02:33	#4 \| Link
2COOL PGC Navigator in Training Join Date: Oct 2002 Location: NTSC Land Posts: 3,552	@mpucoder I was wondering where you were hiding? I knew you couldn't resist answering a technical question. __________________ 2COOL

12th September 2003, 16:51	#6 \| Link
mpucoder Moderator Join Date: Oct 2001 Posts: 3,530	Yes, in addition to the time. It is safe to say 00:00:01.15 is 1 second and 15 frames, but not to say 45 frames. The reason for this is that the true frame rate is 29.97 (actually that's approximate, too) so NTSC uses drop frame timecode. Frame numbers 0 and 1 are dropped whenever needed to adjust the timecode to the actual elapsed time. It is common to drop these frames at the start of every minute not divisible by 10. This gives 18 dropped frame numbers* (not frames) every 10 minutes, so that the (29.97 * 10 * 60) 17982 frames are "counted" as 18000. Actual NTSC framerate is determined by the color subcarrier frequency (3.579545MHz). Each horizontal line is exactly 227.5 cycles of this frequency, and there are 525 lines per frame. So the framerate is 3579545 / 227.5 / 525 = 29.97002617 That small difference creeps up on timecodes and does result in skipped drop counts. Last edited by mpucoder; 12th September 2003 at 16:59.*

12th September 2003, 02:27	#3 \| Link
mpucoder Moderator Join Date: Oct 2001 Posts: 3,530	The last number in the timecode is the frame number within that second. For NTSC this is 0 to 29, for PAL 0 to 24.