The following result are calculated for lip synchronization which is concidered to be *"the most noticeable a/v sync error"*.


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[Wikipedia][1] says 

> For television applications, audio should lead video by no more than 15 milliseconds and audio should lag video by no more than 45 milliseconds. For film, acceptable lip sync is considered to be no more than 22 milliseconds in either direction.


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[The Media and Acoustics Perception Lab][2] says 

> The results of the experiment determined that the average audio leading threshold for a/v sync detection was 185.19 ms, with a standard deviation of 42.32 ms


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[The ATSC][3] says 

> At first glance it seems loose: +90 ms to -185 ms as a “Window of
Acceptability”

and 

>  - Undetectable from -100 ms to +25 ms
>  - Detectable at -125 ms & +45 ms
>  - Becomes unacceptable at -185 ms & +90 ms

> (– Sound delayed,+ Sound advanced)


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**To conclude**

The results aren't so far from one another.
It seems that the maximum acceptable delay is around 150ms, which is 9 frames at 60 frame per second.



  [1]: http://en.wikipedia.org/wiki/Audio_to_video_synchronization
  [2]: http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4599253&url=http://ieeexplore.ieee.org/iel5/11/4604792/04599253.pdf?arnumber=4599253
  [3]:http://www.atsc.org/cms/pdf/audio_seminar/12%20-%20JONES%20-%20Audio%20and%20Video%20synchronization-Status.pdf