Fade Between Two Music Tracks in-progress in Pygame

Question

My intention is to have two music tracks, which are similar in nature, fade between each other at various times. When such a fade occurs, one music track should fade from full volume to muted in a short period of time, and, simultaneously, the other track should fade from 0 to 100 and continue playing from the same time index. They must be able to do this dynamically at any time - when a certain action occurs, the fade will occur and the new track will start playing at the same position that the other one left off at.

This might be plausible by either using volume manipulation or by starting and stopping the music (however, it appears that only a "fadeout" option exists, and there is a lack of a "fadein" option). How can I do this? What is the best method, if any, that exists? If it is impossible using Pygame, alternatives to Pygame are acceptable.

Answer 1

This isn't exactly an answer to the question, but for future-googlers I wrote a script to fade-in my music from volume 0 in the morning and this is what I used:

max_volume = 40 
current_volume = 0

# set the volume to the given percent using amixer
def set_volume_to(percent):
    subprocess.call(["amixer", "-D", "pulse", "sset", "Master", 
                     str(percent) + "%", "stdout=devnull"])

# play the song and fade in the song to the max_volume 
def play_song(song_file):
    global current_volume
    print("Song starting: " + song_file)
    pygame.mixer.music.load(song_file)
    pygame.mixer.music.play()

    # gradually increase volume to max
    while pygame.mixer.music.get_busy():
        if current_volume < max_volume: 
            set_volume_to(current_volume)
            current_volume += 1

        pygame.time.Clock().tick(1)

 play_song("foo.mp3")