Different amount of frames for same track

Question

In the jukebox.c example of libspotify I count all frames of the current track in the music_delivery callback. When end_of_track is called the frames count is different each time I played the same track. So end_of_track is called several seconds after the song is over. And this timespan differs for each playback.

How can I determine if the song is really over? Do I have to take the duration of the song in seconds and multiply it with the sample rate to take care when the song is over?

Why are more frames delivered than necessary for the track? And why is end_of_track not called on the real end of it? Or I am missing something?

Answer 1

end_of_track is called when libspotify has finished delivering audio frames for that track. This is not information about playback - every playback implementation I've seen keeps an internal buffer between libspotify and the sound driver.

Depending on where you're counting, this will account for the difference you're seeing. Since the audio code is outside of libspotify, you need to keep track of what's actually going to the sound driver yourself and stop playback, skip to the next track or whatever you need to do accordingly. end_of_track is basically there to let you know that you can close any output streams you may have from the delivery callback to your audio code or something along those lines.