I'm not really into mp3, but not too long ago there was talk that at least one of the download sites was offering "limited play" downloads. You rent them for a specific period of time, (or number of plays?,) and when the time is up that tune ceases to be playable.

I can see that a "timestamp" could be included in the downloaded file, but for it to have any meaning to a playback device the player would have to look for it, recognize it, and block the tune.

Lack of personal interest prevented my following the status of this, but the warning was given that some download services are considering your payment as a "time limited rental" and not a purchase of the file. One would have to read the EULA for the download site to know, I suppose.

John