[HELP] Audio/video out of sync in output

[Selur]

I can see the combing effect though which I've read is a good indicator of interlaced content.

You also see combing artifacts on telecined content.
To know what your content is (interlaced, telecined, some other pull-down, progressive, mix of those) you need to look at the fields, easy way to do this is to look at the source:
When there are no combing artifacts then the clip is progressive.
When there are only combing artifacts on some scenes you got mixed content. -> more analysis needed
When there are combing artifacts: -> more analysis needed
For analysis you bob deinterlace the content and look whether there are duplicates.
no duplicates: the content is normal interlaced
duplicates that follow a pattern: some pull-down, or frame duplication; if you are lucky just telecined or simple frame duplication. (see: https://en.wikipedia.org/wiki/Telecine)
duplicates that do not follow a patter: manual scripting is needed to properly handle this

Isn't the 10s sample enough for identifying?

I can tell you from the 10s that that sample is properly interlaced content.
(when bobbed each interpolated frame is different from it's predecessor)
So your source is probably NTSC interlaced, but you should look out for that if you convert NTSC->PAL.

Cu Selur