@client.command(pass_context=True)
async def tube(ctx, url):
    server = ctx.message.server
    voice_client = client.voice_client_in(server)

    player = await voice_client.create_ytdl_player(url, after=lambda: check_queues(server.id))
    players[server.id] = player

    player.start()

def check_queues(server_id):
    if queues[server_id] != []:
        player = queues[server_id].pop(0)
        players[server_id] = player
        player.start()