$position = 10;
$id3_end = 10 + $id3_size;
while ($position < $id3_end) {
   seek FH, $position, SEEK_SET;
   # read $frame_id, $frame_size, and $frame_flags
   $position += 10 + $frame_size;
   last if $frame_id =~ /\W/ || $position > $id3_end;
   # do something with $frame_id
}