[opendtv] A bit OT: 24 Frames Drop Frame Timecode
- From: "Russ Wood" <russ.wood@xxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 30 Nov 2007 09:44:51 -0000
Hi from a long-time lurker from across the pond. I don't know where
else to ask this question but I hope there are some experts on here with
the answer.
24 fps video derives from the film world and in order to make it easily
transmittable in a US TV environment this is often resampled at 23.976
fps.
When 29.97 fps video is used the timecode is often drop-frame to make
elapsed times closer to real time.
The company I work for (Softel) makes captioning workstations among
other things and we are being asked by our customers to use 23.976
drop-frame timecode. The algorithm for 29.97 drop-frame is not really
applicable for 23.976 so what algorithm should we use? Is there a
standard anywhere that defines this.
The following algorithm gives a drift of < 1 frame per 24 hours:-
1) When the seconds digits are 59 go direct from hh:mm:59:23 to
hh:mm:00:01
2) When the minute least significant digit is even go direct from
hh:mm:59:23 to hh:mm:00:02
2a) Except when the minute digits are 00 or 16 or 30 or 44 (Note
15 and 45 are not even numbers)
2b) And hour is not 00 or 03 or 06 or 09 or 12 or 15 or 18 or 21
I don't know of any equipment out there that actually generates or reads
23.976 DF timecode but our customers are nevertheless asking for DF.
Russ Wood - Softel Ltd. Pangbourne UK
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