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

Robert Kr├╝ger krueger at lesspain.de
Wed Jan 13 15:13:37 CET 2016


On Wed, Jan 13, 2016 at 3:06 PM, Phil Rhodes <phil_rhodes at rocketmail.com>
wrote:

> I'd be a very careful here.
> Linear timecode (which is fundamentally an audio signal) cannot represent
> a value of more than two in the tens-of-hours position, because only two
> bits are allocated to it. Although other systems may be more forgiving, LTC
> is still very commonly used.
> Furthermore, the standards which specify various types of MXF refer to
> "timecode time addresses" which mirror LTC timecode in that they "consist
> of 64 data bits... 26 bits specify hours, minutes, seconds and frames...
> The combination of these values is the time address of the SMPTE 12M-1
> timecode value. "
> At least some types of MXF will therefore suffer the same limitation.
> The standard I have always referred to is SMPTE-12M (now two documents). I
> don't have access to my copy of 12M right now, and I can't recall if it
> specifically disallows time beyond 24 hours, but I would suggest that the
> safest approach to reject hours > 24 as it is far from universally
> supported. Whenever I have written implementations of 12M, which I have
> done at least three times, I have rejected hours > 24 on this basis.
> P
> __
>

Thanks a lot for the explanation.

Robert


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