[FFmpeg-user] Why is it possible to set a timecode with 24:00:00:00 and beyond?

[Christoph Gerstbauer]

Am 13.01.2016 um 22:30 schrieb Dave Rice:
>> On Jan 13, 2016, at 9:25 AM, Bouke / VideoToolShed <bouke at videotoolshed.com> wrote:
>>> On Jan 13, 2016, at 14:17, Robert Krüger <krueger at lesspain.de> wrote:
>>>
>>> On Wed, Jan 13, 2016 at 12:53 PM, Christoph Gerstbauer <
>>> christophgerstbauer at gmail.com> wrote:
>>>
>>>> FFmpeg allows me to set a timecode of 24:00:00:00 and beyond.
>>>>
>>>> e.g "-timecode 24:00:00:00"
>>>>
>>>> When I make an MXF D10 for example, the value of 24:00:00:00 is still in
>>>> the file.
>>>> Most but not all programs ignore this and display 00:00:00:00 correctly.
>>>>
>>>> Here are some sample extractions of the timecode offset value in different
>>>> mxf d10 files generated by ffmpeg:
>>>>
>>>> PAL 25fps:
>>>>
>>>> -timecode 12:34:56:11  -> in file: 11477b hex -> 1132411 dec
>>>>
>>>> -timecode 10:00:00:00 -> in file: 0dbba0 hex -> 900000 dec
>>>>
>>>> -timecode 20:00:00:00 -> in file: 1b7740 hex -> 1800000 dec
>>>>
>>>> -timecode 23:59:59:24 -> in file: 20f57f hex -> 2159999 dec
>>>>
>>>> -timecode 24:00:00:00 -> in file: 20f580 hex -> 2160000 dec -> 24h
>>>>
>>>> -timecode 24:00:00:01 -> in file: 20f581 hex -> 2160001 dec
>>>>
>>>> -timecode 25:00:00:00 -> in file: 225510 hex -> 2250000 dec -> 25h
>>>>
>>>>
>>>> NTSC 30fps
>>>>
>>>> -timecode 23:59:59;29 -> in file: 2782df hex -> 2589407 dec
>>>>
>>>> -timecode 24:00:00;00 -> in file: 2782e0 hex -> 2589408 dec
>>>>
>>>>
>>>> Why is this possible to set a timecode after 23:59:59:XX?
>>>> Is there a usecase?
>>>>
>>> I wasn't able to find any official spec that says what the limit for the
>>> hour part is but since it in the general case does not define a time of day
>>> but an offset, why limit it to 25 hours and not use the full 100? On a
>>> side-note, I have not come across a real-world use case for a timecode of
>>> that magnitude either.
>>>
>> Some forms of TC just lack the space to store higher numbers IIRC (LTC / VITC, perhaps also in MpegII frame headers)
>> But there is logic in not going higher, as it is ‘time’.
>> For a real world use case, in the old days of tape, a reelname most of the time corresponded with the hour.
>> So a production with more than 24 tapes needed better administration in reel names that had to be written on the tape and box.
> FWIW QuickTime timecode flags includes a "24 hour max" flag to clarify when it is and is not enabled in a timecode track, but >24 hour values are certainly allowed in the QuickTime spec. https://developer.apple.com/library/mac/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html <https://developer.apple.com/library/mac/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html>
> Dave Rice
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> ffmpeg-user at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/ffmpeg-user

Hello Dave,

as seen in SMPTE S012M Time and Control Code from 1999:

Page 2 of 21 pages:

"4.2 Time address of a frame
Each frame shall be identified by a unique and complete
address consisting of an hour, minute, second,
and frame number. Refer to ANSI/SMPTE 258M for
standard formats used to display frame-based time.
The hours, minutes, and seconds follow the ascending
progression of a 24-hour clock beginning with 0
hours, 0 minutes, and 0 seconds to 23 hours, 59
minutes, and 59 seconds. "

It would be interesting what would be mentioned in the newest SMPTE 
version about timecode.
Does anyone have this standard paper? (Year 2014)

Best Regards
Christoph