user3643: If I have an interview or lecture style video and the audio is out of sync, by how much can it be out of sync before the average person would easily notice?
I'm currently trying to create an HTML5 player that sometimes has the video and audio in separate elements, meaning the video and the audio buffer and play at separate times. I've developed a decent code that keeps them synced (it's a harder problem then it should be). The current code pauses the video and the audio elements if they are off by 0.1 seconds, adjusts the time of the video element to the audio element, waits for oncanplay event, then plays both. My question is whether 0.1 seconds off in audio/video sync is too much. Would a common user notice a 0.1 seconds sync disparity? What's the highest I can go before the common user might notice the lips don't quite match the voice? Does any large organization have an official standard on this?

user14523: There are, in fact, several standards on audio/video or lip sync. The problem is, they can't all agree on what the acceptable error is. What is well understood is that if the audio lags the video it is less noticeable, because that is natural. Something that is further away will be seen before it is heard. In the list below, a negative number is the audio lagging the video and positive is the audio leading the video.

ATSC IS-191: -45ms to 15ms
EBU R37-2007: -60ms to 40ms
ITU BT.1359-1: -125ms to 45ms
ITU BR.265-9: -22ms to 22ms

ITU BT.1359 was based off studies done with average viewers, but relied on significantly older technology. The ATSC and EBU recommendations rely on expert opinions. The methodologies don't give you a hint at which one is right. I've worked at facilities that used -2 frames to 1 frame (roughly -33ms to 16ms at 60fps) as an easy to remember guideline with very few viewer complaints about lip sync.
Even with the disagreement, 0.1s (100ms) of error will almost always be noticeable, unfortunately.

3643: <p>If I have an interview or lecture style video and the audio is out of sync, by how much can it be out of sync before the average person would easily notice?</p>

<p>I'm currently trying to create an HTML5 player that sometimes has the video and audio in separate elements, meaning the video and the audio buffer and play at separate times. I've developed a decent code that keeps them synced (it's a harder problem then it should be). The current code pauses the video and the audio elements if they are off by 0.1 seconds, adjusts the time of the video element to the audio element, waits for <code>oncanplay</code> event, then plays both. My question is whether 0.1 seconds off in audio/video sync is too much. Would a common user notice a 0.1 seconds sync disparity? What's the highest I can go before the common user might notice the lips don't quite match the voice? Does any large organization have an official standard on this?</p>
 14523: <p>There are, in fact, several standards on audio/video or lip sync. The problem is, they can't all agree on what the acceptable error is. What is well understood is that if the audio lags the video it is less noticeable, because <a href="https://web.archive.org/web/20150328054944/https://www.smpte.org/sites/default/files/2013-12-10-Lip-Sync-Briscoe-V2-Handout.pdf" rel="nofollow noreferrer">that is natural</a>. Something that is further away will be seen before it is heard. In the list below, a negative number is the audio lagging the video and positive is the audio leading the video.</p>
<ul>
<li><strong><a href="https://www.webcitation.org/60UbU5Ziv" rel="nofollow noreferrer">ATSC IS-191</a>:</strong> -45ms to 15ms</li>
<li><strong><a href="https://tech.ebu.ch/docs/r/r037.pdf" rel="nofollow noreferrer">EBU R37-2007</a>:</strong> -60ms to 40ms</li>
<li><strong><a href="https://www.itu.int/rec/R-REC-BT.1359-1-199811-I/en" rel="nofollow noreferrer">ITU BT.1359-1</a>:</strong> -125ms to 45ms</li>
<li><strong><a href="https://www.itu.int/rec/R-REC-BR.265-9-200402-W/en" rel="nofollow noreferrer">ITU BR.265-9</a>:</strong> -22ms to 22ms</li>
</ul>
<p>ITU BT.1359 was based off studies done with average viewers, but relied on significantly older technology. The ATSC and EBU recommendations rely on expert opinions. The methodologies don't give you a hint at which one is right. I've worked at facilities that used -2 frames to 1 frame (roughly -33ms to 16ms at 60fps) as an easy to remember guideline with very few viewer complaints about lip sync.</p>
<p>Even with the disagreement, 0.1s (100ms) of error will almost always be noticeable, unfortunately.</p>
