Inspect full first row of video frame.

oscilloscope=x=0.5:y=0:s=1

Inspect full last row of video frame.

oscilloscope=x=0.5:y=1:s=1

Inspect full 5th line of video frame of height 1080.

oscilloscope=x=0.5:y=5/1080:s=1

Inspect full last column of video frame.

oscilloscope=x=1:y=0.5:s=1:t=1