get_song: fix signatureTimestamp (#196)

ytmusicapi/helpers.py

@@ -3,6 +3,7 @@
 from http.cookies import SimpleCookie
 from hashlib import sha1
 import time
+from datetime import date
 from functools import wraps
 import locale
 from ytmusicapi.constants import *
@@ -102,6 +103,10 @@ def get_authorization(auth):
     return "SAPISIDHASH " + unix_timestamp + "_" + sha_1.hexdigest()
 
 
+def get_datestamp():
+    return (date.today() - date.fromtimestamp(0)).days
+
+
 def to_int(string):
     number_string = string.split(' ')[0]
     try:

ytmusicapi/mixins/browsing.py

@@ -542,11 +542,13 @@ def get_album(self, browseId: str) -> Dict:
 
         return album
 
-    def get_song(self, videoId: str) -> Dict:
+    def get_song(self, videoId: str, signatureTimestamp: int = None) -> Dict:
         """
         Returns metadata and streaming information about a song or video.
 
         :param videoId: Video id
+        :param signatureTimestamp: Provide the current YouTube signatureTimestamp.
+            If not provided a default value will be used, which might result in invalid streaming URLs
         :return: Dictionary with song metadata.
 
         Example::
@@ -702,10 +704,13 @@ def get_song(self, videoId: str) -> Dict:
 
         """
         endpoint = 'player'
+        if not signatureTimestamp:
+            signatureTimestamp = get_datestamp() - 1
+
         params = {
             "playbackContext": {
                 "contentPlaybackContext": {
-                    "signatureTimestamp": 18766
+                    "signatureTimestamp": signatureTimestamp
                 }
             },
             "video_id": videoId