[Ardour-Dev] Ardour Timecode

Robin Gareus robin at gareus.org
Fri Nov 2 01:29:42 PDT 2012

On 11/01/2012 11:19 PM, John Emmas wrote:
> I'm not sure if this comment from Reuben is stipulated in a
> specification somewhere but it makes some sense....

Just when I thought we had it all worked out... :)

> On 31 Oct 2012, at 05:04, Reuben Martin wrote:
>> Most editors lock to the DF timing. But then after the content is
>> rendered and played out for broadcast, it's played out at the
>> 30/1.001 rate.
> Consider that an error of 3.6mS per hour would accumulate to an error
> of 1 whole frame every 9.25 hours or so.  Therefore you'd expect that
> to be correctable in the dropframe specification.  But it isn't
> Which suggests that for the purposes of production, editing and
> number calculation, 29.97 is assumed to be the actual frame rate
> (precisely, not approximately).  Only when the picture actually gets
> transmitted does the rate become slightly faster, at (30 *1000 /
> 1001).

Wouldn't that also imply that audio is resampled on transmission - or
A/V sync is broken.

> That makes considerable sense 

Not to me. Simplify one end, complicate another.

> - as well as implying that Avid's
> 2997/100 frame rate is correct - at least as far as the _calculated_
> timecode values are concerned.  Interesting....

It indeed addresses the issue of having multiple reels shot on different
days (> 24h timecode). The resulting master is usually < 120 mins.
Correcting the playout speed of the latter is easier than dealing with
offsets throughout the project.

In fact it makes no real difference when the material is shot with
rec-run timecode which is still very common. The audio is re-aligned for
each take and takes are rarely longer than a minute.

But now that freerun (time-of-day) timecode is finally taking over, this
could lead to problems: Cameras generate timecode at the shutter speed
which for all professional cameras [that I read the manual for] is at a
/1.001 rate [when using fractional frame rates].

If a NLE imports this at 30 * 999 / 1000 there will already be offsets
to the audio at the beginning of the edit process. -- 2013 the year of
the clapper. Luckily most films are still shot at 23.986ndf :)


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