This has been discussed a lot in the past. The problem is that that connector being AV (audio and video) needs a video source to work if not it mutes the sound. The normal 4 ring jack fits and if you pull it out slightly it has been known for the video to think it has a signal and unblank the display and play but this is unreliable and may cause the display to work at the wrong frequency. In the past this would break a monitor!! I haven't yet tried a video mp4 player to see if it puts a signal on to the video line when playing mp3s but that may work.