[Ardour-Dev] Ardour Timecode

[Fons Adriaensen]

On Thu, Nov 01, 2012 at 09:59:01PM +0100, Robin Gareus wrote:

> a)  At 30fps the intention of dropframe timecode is to drop 108 frames per realtime hour.
> b)  At 30fps the intention of dropframe timecode is to drop 108 frames per 1.001 realtime hours.

It should have done (a) but it does (b).

DF means to skip the first two frames of every minute, except the first
minute of every ten. That means on average 18 frames for every 18000.
That would compensate exactly for an NTSC color frame rate of 30 * 0.999,
and it's an easy mistake to assume that *is* the actual rate. But it isn't,
it's 30 / 1.001, a difference of one PPM.

It's a mess, and even more so if you consider that the frame rate correction
wasn't necessary at all - they could have adjusted the sound subcarrier for
the same effect (avoiding visible interference from the color subcarrier).

Ciao,

-- 
FA

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It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)