Here is a simpler approach to your problem:

while (<DATA>) {
   next if /^\s*$/;
   print("#$1 "), next if /^(\d+)$/;
   print("$1;$2;$3;$4 $5;$6;$7;$8\n"), next
      if /^(\d+):(\d+):(\d+),(\d+) --> (\d+):(\d+):(\d+),(\d+)$/;
   print;
}

__DATA__
1
00:00:38,585 --> 00:00:40,519
What's wrong?

2
00:00:40,554 --> 00:00:43,148
I think I hit something.
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