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

[Simon A. Eugster]

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