Line number
Specifies the line number to trigger on. An absolute line number system is used, meaning that the lines from field 1 are numbered 1 —> x, and the lines from field 2 are labeled x+1 —> y.
The number of lines available depends on the format. For NTSC, the valid range is 1 to 525. For PAL and SECAM, the valid range is 1 to 625.