Automatic music rating based on listening habits

I've created a Winamp-like music player in Delphi. Not so complex, of course. Just a simple one.

But now I would like to add a more complex feature: Songs in the library should be automatically rated based on the user's listening habits.

This means: The application should "understand" if the user likes a song or not. And not only whether he/she likes it but also how much.

My approach so far (data which could be used):

• Simply measure how often a song was played per time. Start counting time when the song was added to the library so that recent songs don't have any disadvantage.
• Measure how long a song was played on average (minutes).
• Starting a song but directly change to another one should have a bad influence on the ranking since the user didn't seem to like the song.
• ...

Could you please help me with this problem? I would just like to have some ideas. I don't need the implementation in Delphi.

Measure how long a song was played on average (minutes).

I don't think this is a good metric, because a long song would gain an unfair advantage over a short song. You should use a percentage instead:

avg. time played / total song length