An example of how to track the percentage of multimedia file being played.

TrackerMain.kt

import java.util.BitSet

const val MIN = 6
const val SEC = 11

fun countSec(m: Int, s: Int): Int {
    return (60 * m) + s
}

val COUNT_SEC = countSec(MIN, SEC)

val arr = BitSet(COUNT_SEC)
var start = 0
var end = 0
var isPlayed = false

fun play(sec: Int) {
    checkSecIsValid(sec)
    isPlayed = true
    start = sec
}

fun stop(sec: Int) {
    checkSecIsValid(sec)
    isPlayed = false
    end = sec
    arr.set(start, end+1, true)
}

fun scroll(from: Int, to: Int) {
    checkSecIsValid(from)
    checkSecIsValid(to)
    if (isPlayed) {
        end = from
        arr.set(start, end+1, true)
        start = to
    }
}

@UseExperimental(kotlin.ExperimentalStdlibApi::class)
fun calculate(arr: BitSet, totalSec: Int) : Double {
    val longArray = arr.toLongArray()
    var bc = 0;
    for (l in longArray) {
        bc += l.countOneBits()
    }
    return (bc.toDouble() / totalSec) * 100
}

fun display(arr: BitSet) {
    println("(start,end): (" + start + ", " + end + ")");
    for(i in 0..COUNT_SEC) {
        print(if (arr.get(i)) 1 else 0);
    }
    println("");
}

fun checkSecIsValid(sec: Int) {
    if (sec < 0 || sec > COUNT_SEC) {
        throw IllegalArgumentException(sec.toString() + " is out of (0.." + COUNT_SEC + ")")
    }
}

fun main() {
    println("Arr count: " + arr.size())
    play(0)
    display(arr)
    stop(14)
    display(arr)
    scroll(14, 40)
    display(arr)
    play(40)
    display(arr)
    stop(42)
    display(arr)
    scroll(42, 1)
    display(arr)
    play(1)
    display(arr)
    stop(300)
    display(arr)
    println("Calc: " + calculate(arr, COUNT_SEC) + " %")
}