Add Spotify volume normalization to Google Cast devices

turnitdown.py

#!/usr/bin/python3
#
# turnitdown.py - normalize Spotify playback volume on Google Cast devices
#
# Dependencies: pychromecast, spotipy
#
# Usage: register a Spotify app and put the credentials in the
# SPOTIPY_CLIENT_ID and SPOTIPY_CLIENT_SECRET environment variables.
# Then just launch the script. It will autodetect all cast devices
# on the network.

import logging
import time
import pychromecast
import spotipy
from spotipy.oauth2 import SpotifyClientCredentials

VOLUME_RANGE = 34.0
MAX_VOL = 1.0
MIN_VOL = 0.001
WIGGLE = 0.01
FUDGE = 0.001

class VolumeFixer(pychromecast.controllers.media.MediaStatusListener):
    def __init__(self, sp, cc):
        self.sp = sp
        self.cc = cc
        self.last_track = None
        self.last_loudness = None
        self.ref_vol = None

    def new_media_status(self, status: pychromecast.controllers.media.MediaStatus):
        if status.content_type != "application/x-spotify.track":
            return

        track = status.content_id
        if track == self.last_track:
            return
        
        try:
            af = self.sp.audio_features([track])
            loudness = af[0]["loudness"]
        except:
            return

        if self.last_loudness is None:
            self.last_loudness = loudness

        cur_vol = self.cc.status.volume_level
        cur_ref = self.last_loudness + VOLUME_RANGE * (cur_vol - 1)
        
        if (self.ref_vol is None or
            (cur_vol > (MIN_VOL + FUDGE) and cur_ref > (self.ref_vol + WIGGLE)) or
            (cur_vol < (MAX_VOL - FUDGE) and cur_ref < (self.ref_vol - WIGGLE))):
            self.ref_vol = cur_ref

        new_vol = min(MAX_VOL, max(MIN_VOL, (self.ref_vol - loudness) / VOLUME_RANGE + 1))
        
        print(f"[{self.cc.device.friendly_name}] Playing {status.title} ({track}) loudness {loudness} volume {cur_vol} -> {new_vol} (ref: {self.ref_vol})")
        
        self.cc.set_volume(new_vol)
        self.last_loudness = loudness
        self.last_track = track

sp = spotipy.Spotify(auth_manager=SpotifyClientCredentials())

print("Locating chromecasts...")

chromecasts, browser = pychromecast.get_chromecasts()

print("Found chromecasts:")
for cc in chromecasts:
    print(f" - {cc.device.friendly_name} ({cc.device.cast_type})")
    cc.wait()
    cc.media_controller.register_status_listener(VolumeFixer(sp, cc))

print("Waiting for events...")

while True:
    time.sleep(1)