What number comes next 2 12 1112 31112 132112 1113122112 311311222112?

13211321322112

This line describes the last line. Each two digits describes how often a number repeats. One three, two one's, one three, two one's, three two's, three two's, two one's, one two.

The problem with the sequence provided is the fourth set where there has been a typo (31112) should be (3112).