[Lumiera] Audio editing

hendrik at topoi.pooq.com hendrik at topoi.pooq.com
Sun Jul 5 21:45:31 CEST 2009


On Sun, Jul 05, 2009 at 05:15:38PM +0200, Christian Thaeter wrote:
> Ichthyostega wrote:
> >> Juan Pablo Bouza wrote:
> >>> ...that it didn´t support frame rates with fractions, such as 23.976....
> > 
> > Christian Thaeter schrieb:
> >> Just a note: using floating point for framerates is almost always a bad idea.
> >> Rational numbers (numerator/demominator) are much better...
> > 
> > And additionally, could you please enlighten me what would be the prospective
> > use of such a fractional frame rate for audio? For everything I am aware off,
> > the frame rate was fixed to a limited set of values dictated by hardware,
> > eg. 8000, 44100, 48000, 96000, 192000, etc.

Then you might want exact numbers like 78334/48000.

> > 
> > But maybe I'm overlooking an interesting use case here?
> 
> That are sample rates, dunno if one wants to call single audio samples a
> frame :)...
> 
> Anyway, video frame rates coming into play when one wants to sync audio
> with video which was the case here. Even worse, a lot of (consumer)
> cameras clock drift depending on temperature, moon-phase and mood, the
> audio sample rate is not exactly 48kHz but some Hz more or less (i'd
> guess frame rates may drift too). Some people told me that this gives
> noticeable audio desyncs depending if the camera was warm or cold. We'll
> face endless fun with such things :). I think some automation for
> frame/sample rate fine adjustment controling some noise gate
> (extend/compact silent phases) or frame drop (or doubling) might be a
> forseeable tool to correct that.

So the audio sample rate and the video frame rate need to be driven by 
the same timer.  If this is'nt done in a videw camera, the camera is 
designed broken.  It we're talking about synching independently 
recorded audi and video (like comparing different people's recordings 
of the Kennedy assassination), it takes real work in the editor.  But 
using floating point for anything but compatibility with another 
application's floating point just introduces additional errors.

-- hendrik



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