[Kdenlive-devel] Feature request: Sync External Audio Automatically

[Gabriel Gazzán]

Record a fast bouncing ball, chances are that you will catch it in contact
with the floor in *none* of the frames of the video.
Where will you put the sound fx? The only way to put this kind of sound fx
right is to have more than *frame* presicion! People who animate, like me,
have learned this a long ago.
That said I know there might be technocal problems in implementing this
functionality, and I totally undestand that this could not make it into
Kdenlive soon. That's perfectly ok.

g


2012/2/10 Simon A. Eugster <simon.eu at gmail.com>

> On 02/09/2012 04:45 AM, Brian Matherly wrote:
> >> 2012/2/8 Gabriel Gazzán<gabcorreo at gmail.com>:
> >
> >>> I think frame level accuracy is usually "not enough" precision, as also
> >>
> >> it is good enough for me
> >
> >
> > It really depends on your use case.
> >
> > The ITU did a study and found that the threshold of detectability of lip
> sync errors is about +45 ms to –125 ms (audio early to audio late) and that
> the threshold of acceptability is about +90 ms to –185 ms. Apparently it is
> generally more tolerable for the audio to be slightly delayed than for it
> to be slightly early.
> >
> >
> > If you only synchronize on video frame boundaries, then the worst case
> scenario would be +20ms or -20ms for 25fps video (that is +/- 1/2 video
> frame). The ITU research supports Dan's comment that most people can't even
> detect that much error. That may be acceptable if your project will be
> consumed directly. But if the output of your project is destined for
> further processing (like being transcoded by another system, or being sent
> through a broadcast chain), the down stream systems may add to the AV sync
> error. If the error stacks up, it could exceed the thresholds of
> detectability or possibly even the threshold of acceptability.
> >
> > So the amount of A/V error that is appropriate for your project depends
> on what you plan on doing with it.
> >
> > ~BM
>
> Thanks a lot for this information!
> Did they also test detectability of sync errors of hard sound effects?
> Could it be lower there?
> Maybe I'm a little too sensitive here, I hate watching videos in German
> since they usually are badly synched (obviously ... different language)
> and I often have to force myself to look somewhere else than to the
> actors' faces in the first minutes.
> So we could start with frame accuracy first.
> Also, thanks Dan for the hints.
>
> Simon
>
>
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