[eqvinox]

> There's no need to synchronize the time with other sources,

The problem isn't synchronicity, it's syntonicity, albeit only to a limited degree. What you need to know is: how much is your local audio sample clock off from the source audio clock, and from your (distinct) video output clock.

But microseconds precision is indeed perfectly fine, ideally with some way to get simultaneous timestamps from the different clocks at least for the local clocks.

I don't see PTP playing into this either, if anything the associated hardware timestamping features might be a "nice to have to make it perfect", but noone I know wires the audio clock into the PTP timestamping unit.