Understanding "AV sync issue" at timestamp 0:00:00

[idaGaNnHUL]

Hopefully a fairly straightforward question: what does an overlapping frame notice at timestamp 0:00:00 imply about the underlying content? Here's an example:

Code: Select all

AV sync issue in stream 3 at 0:00:00 : 0 frame(s) dropped to reduce audio skew to +21.666ms
AV sync issue in stream 7 at 0:00:00 : 0 frame(s) dropped to reduce audio skew to +21.666ms
AV sync issue in stream 8 at 0:00:00 : 0 frame(s) dropped to reduce audio skew to +21.666ms
AV sync issue in stream 9 at 0:00:00 : 0 frame(s) dropped to reduce audio skew to +21.666ms
AV sync issue in stream 3,7,8,9 at 0:00:00 with duration of 21.666ms : encountered overlapping frame, audio skew is +21.666ms

There are lots of threads about AV sync across the forum, and the closest to an explanation I've come is this post from 2021. It's fairly speculative though, and it would be good to understand if its assumptions are correct or not.

Any insight would be very welcome. I want to be clear that the above seems to cause me no problems in practice, and that I'm asking primarily out of a desire to understand it. Thanks!