[DanCooper]

Image 3: Real Mediainfo from the file. It shows that the MKV has 3 audio tracks, not just one.

Ok, indeen that's strange/wrong. Can you send me a snipped of this video, e.g. created with ffmpeg?

Code:

ffmpeg -ss 00:01:00 -i input.mp4 -to 00:02:00 -c copy output.mp4

-i: This specifies the input file. In that case, it is (input.mp4).
-ss: Used with -i, this seeks in the input file (input.mp4) to position.
00:01:00: This is the time your trimmed video will start with.
-to: This specifies duration from start (00:01:40) to end (00:02:12).
00:02:00: This is the time your trimmed video will end with.
-c copy: This is an option to trim via stream copy. (NB: Very fast)
The timing format is: hh:mms