It was completely wrong. mpv will buffer data ahead of where the CD
currently is playing. When enough data was buffered into the next track,
the track info is printed regardless of where the stream position
actually is. Depending on the user settings, you can get mpv to buffer
minutes ahead. Printing a message when the track changes might be nice,
but this isn't the right place to do it. Some other mechanism would need
to be leveraged, but I'm not going to bother figuring it out.