A script I use to preview looping music

loop

#!/usr/bin/env python3

import pyglet

class LoopingGroup(pyglet.media.SourceGroup):
    def _advance(self):
        if not self._sources: return
        print('loop seek!')
        source = self._sources[0]
        super()._advance()
        source.seek(0)
        self._sources.append(source)

def make_looper(source):
    out = LoopingGroup()
    out.add(source)
    return out

class Music:
    def __init__(self, intro, loop):
        if intro: self.intro = pyglet.media.load(intro)
        self.loop = make_looper(pyglet.media.load(loop))

        self.group = pyglet.media.SourceGroup()
        if intro: self.group.add(self.intro)
        self.group.add(self.loop)

    def queue(self, player):
        player.queue(self.group)

def main(argv):
    intro = None
    loop = None

    while argv:
        el = argv.pop(0)
        if el == '-i' or el == '--intro':
            intro = argv.pop(0)
        elif not loop:
            loop = el
        else:
            print('usage: loop [-i INTRO_FILE] LOOP_FILE')
            exit(1)

    player = pyglet.media.Player()
    Music(intro, loop).queue(player)
    player.play()
    pyglet.app.run()


if __name__ == '__main__':
    from sys import argv
    main(argv[1:])