YouTube offers different playback speed options for users. This allows users to increase or decrease the speed of the video content. Given the actual duration and playback speed of the video, calculate the playback duration of the video.
playbackDuration("00:30:00", 2) ➞ "00:15:00"
playbackDuration("01:20:00", 1.5) ➞ "00:53:20"
playbackDuration("51:20:09", 0.5) ➞ "102:40:18"