Open up Avidemux and drag your video into it.

For main stages timing starts on the second-to-last full white frame, which is 0.00. We look for that frame and press "A".

Go to the first frame Mario grabs the star and press "B". The time in the bottom right is the single star time.

For bowser courses with no star grab timing starts on the second-to-last full black frame, which is 0.00. We look for that frame and press "A".

Go to the first frame the black star border appears and press "B". The time in the bottom right is the single star time. The timing for this in particular is identical to XCam.

For bowser courses with star grab and all other secret stars timing starts on the second-to-last full black/white frame, which is 0.00. We look for that frame and press "A".

Go to the first frame Mario grabs the star and press "B". The time in the bottom right is the single star time.