In music player apps, the next button will change the track and play the next track in the playlist. But on pressing the previous button the track is not changed. Instead the current track starts from the beginning. And if previous button is pressed again then it will go to the previous track in the playlist.
I was curious if there is a reason behind this.
The timeline is represented linearly. Start -> End.
If you would have noticed most of the players also have the Fast Forward and Rewind buttons as the same as Next and Previous buttons.
Suppose if the user is almost near the end of the track and wants to play the song from the first: User can
(a). rewind (by pressing and holding the Previous tract button) all the way up to the start
(b). Press the previous button (let us say the player would play the previous track instead of the same track) and press the next button to come back to the same track.
(c). Press the previous button (and the player plays the track from first)
The most intuitive of the 3 options is the obvious (c).
Also it is more intuitive if the user presses next button to move the end of the track (which is obviously the start of next track) and back previous button to move to the start of the track.
I hope this makes sense!!
It is perhaps unfortunate that they're called the Previous and Next buttons given it seems to lead to such confusion. “Back” and “forward” may have been better names. But in any case, the answer to your question is that ease of use and practicality trumps logic for this UX. You want a UI that makes the most common tasks easiest to do.
Among the most common tasks for users are:
To replay a song they’re listening too (e.g., because they got interrupted and didn’t hit pause, or maybe they just really like that song).
To skip the song they’re listening too (usually because they just don’t feel like hearing that song right now, not because they necessarily want to get to the next one, which may be unknown if they’re in shuffle mode).
Thus, it makes sense to have a couple buttons that support these tasks with a single press. It’s much less common for a user to want to skip back to a previous song or skip ahead two songs. It's good to support these tasks in some way, but also okay that they take additional effort (two presses).
Actually, “previous” and “next” are logical and consistent names, if you think of them as moving the user to the previous and next break between songs. However, I doubt users would naturally think in those terms.
BTW, I wouldn't say ease-of-use/task-support always trumps logic or consistency. It depends on how illogical or inconsistent the UI is. In this case it's a pretty mild inconsistency and readily mitigated. If any users expected Previous to go to the previous song, and found instead it went to the beginning of the current song, it would be easy and obvious enough to correct and recover by hitting Previous again. But it would be better still to rename the controls.
