title: Subtracting time w/ AWK
body: <p>What I'm trying to achieve is the difference between chapter 1 start time and chapter 2 start time and so on subtracting each chapter start time from the next in the array e.g. 00:05:57 - 00:01:03 = 00:04:54</p>
  
  <pre><code>$ cat ChapterStart 
  00:00:00 00:01:03 00:05:57 00:08:27 00:11:58 00:14:50 00:20:19 00:25:06 00:33:17 00:38:21 00:42:30 00:46:11 00:51:33 01:00:04 01:00:56 01:04:15 01:09:13 01:16:51 01:20:03 01:27:58
  </code></pre>
  
  <p>This simply doesn't work:</p>
  
  <pre><code>#!/bin/bash
  awk 'BEGIN{
  {
   for(i=1;i&lt;=NF;i++){
      m=split($i,t,":")
      n=split($(i+1),w,":")
      chap = (t[1]*3600) + (t[2]*60) + t[3]
      chap_next = (w[1]*3600) + (w[2]*60) + w[3]
      duration = (chap_next - chap)
      print $duration
      }
   }
  }'ChapterStart
  </code></pre>
  
  <p>Any suggestions?  </p>