An IdArray is an array of 32 bit, big endian unsigned integers. Each Id typically represents a track. An empty IdArray indicates an rray with no elements i.e. no tracks are available.
For example the IdArray of:
0x00 0x00 0x00 0x02 0x00 0x00 0x01 0x14 0x00 0x00 0x00 0x13
contains 3 ids with the values of 2, 276, and 19 in that order.