fix: use YouTube-provided thumbnail URLs instead of hardcoded hq720.jpg

Videos without hq720.jpg thumbnails caused mass 404 errors.
Now preserves the actual thumbnail URL from YouTube's API response,
falls back to hqdefault.jpg only when no thumbnail is provided.
Also picks highest quality thumbnail from API (thumbnails[-1])
and adds progressive fallback for subscription/download functions.

server.py

@@ -99,7 +99,6 @@ def proxy_site(env, start_response, video=False):
         if response.status >= 400:
             print('Error: YouTube returned "%d %s" while routing %s' % (
                 response.status, response.reason, url.split('?')[0]))
-
         total_received = 0
         retry = False
         while True:

youtube/channel.py

@@ -406,12 +406,12 @@ def post_process_channel_info(info):
     info['avatar'] = util.prefix_url(info['avatar'])
     info['channel_url'] = util.prefix_url(info['channel_url'])
     for item in info['items']:
-        # For playlists, use first_video_id for thumbnail, not playlist id
+        # Only set thumbnail if YouTube didn't provide one
+        if not item.get('thumbnail'):
             if item.get('type') == 'playlist' and item.get('first_video_id'):
-            item['thumbnail'] = "https://i.ytimg.com/vi/{}/hq720.jpg".format(item['first_video_id'])
+                item['thumbnail'] = "https://i.ytimg.com/vi/{}/hqdefault.jpg".format(item['first_video_id'])
-        elif item.get('type') == 'video':
+            elif item.get('type') == 'video' and item.get('id'):
-            item['thumbnail'] = "https://i.ytimg.com/vi/{}/hq720.jpg".format(item['id'])
+                item['thumbnail'] = "https://i.ytimg.com/vi/{}/hqdefault.jpg".format(item['id'])
-        # For channels and other types, keep existing thumbnail
         util.prefix_urls(item)
         util.add_extra_html_info(item)
     if info['current_tab'] == 'about':

youtube/comments.py

@@ -150,7 +150,7 @@ def post_process_comments_info(comments_info):
         util.URL_ORIGIN, '/watch?v=', comments_info['video_id'])
     comments_info['video_thumbnail'] = concat_or_none(
         settings.img_prefix, 'https://i.ytimg.com/vi/',
-        comments_info['video_id'], '/hq720.jpg'
+        comments_info['video_id'], '/hqdefault.jpg'
     )
 
 

youtube/playlist.py

@@ -106,8 +106,8 @@ def get_playlist_page():
     for item in info.get('items', ()):
         util.prefix_urls(item)
         util.add_extra_html_info(item)
-        if 'id' in item:
+        if 'id' in item and not item.get('thumbnail'):
-            item['thumbnail'] = f"{settings.img_prefix}https://i.ytimg.com/vi/{item['id']}/hq720.jpg"
+            item['thumbnail'] = f"{settings.img_prefix}https://i.ytimg.com/vi/{item['id']}/hqdefault.jpg"
 
         item['url'] += '&list=' + playlist_id
         if item['index']:

youtube/static/js/common.js

@@ -121,11 +121,12 @@ window.addEventListener('DOMContentLoaded', function() {
  * Priority: hq720.jpg -> sddefault.jpg -> hqdefault.jpg -> mqdefault.jpg -> default.jpg
  */
 function thumbnail_fallback(img) {
-    const src = img.src || img.dataset.src;
+    // Once src is set (image was loaded or attempted), always work with src
+    const src = img.src;
     if (!src) return;
 
     // Handle YouTube video thumbnails
-    if (src.includes('/i.ytimg.com/')) {
+    if (src.includes('/i.ytimg.com/') || src.includes('/i.ytimg.com%2F')) {
         // Extract video ID from URL
         const match = src.match(/\/vi\/([^/]+)/);
         if (!match) return;
@@ -138,36 +139,32 @@ function thumbnail_fallback(img) {
             'hq720.jpg',
             'sddefault.jpg',
             'hqdefault.jpg',
-            'mqdefault.jpg',
-            'default.jpg'
         ];
 
         // Find current quality and try next fallback
         for (let i = 0; i < fallbacks.length; i++) {
             if (src.includes(fallbacks[i])) {
-                // Try next quality
                 if (i < fallbacks.length - 1) {
-                    const newSrc = imgPrefix + 'https://i.ytimg.com/vi/' + videoId + '/' + fallbacks[i + 1];
+                    img.src = imgPrefix + 'https://i.ytimg.com/vi/' + videoId + '/' + fallbacks[i + 1];
-                    if (img.dataset.src) {
-                        img.dataset.src = newSrc;
                 } else {
-                        img.src = newSrc;
+                    // Last fallback failed, stop retrying
-                    }
+                    img.onerror = null;
-                }
+                }
-                break;
+                return;
             }
         }
+        // Unknown quality format, stop retrying
+        img.onerror = null;
     }
     // Handle YouTube channel avatars (ggpht.com)
     else if (src.includes('ggpht.com') || src.includes('yt3.ggpht.com')) {
-        // Try to increase avatar size (s88 -> s240)
         const newSrc = src.replace(/=s\d+-c-k/, '=s240-c-k-c0x00ffffff-no-rj');
         if (newSrc !== src) {
-            if (img.dataset.src) {
-                img.dataset.src = newSrc;
-            } else {
             img.src = newSrc;
+        } else {
+            img.onerror = null;
         }
-        }
+    } else {
+        img.onerror = null;
     }
 }

youtube/subscriptions.py

@@ -1089,12 +1089,26 @@ def serve_subscription_thumbnail(thumbnail):
             f.close()
             return flask.Response(image, mimetype='image/jpeg')
 
-    url = f"https://i.ytimg.com/vi/{video_id}/hq720.jpg"
+    image = None
+    for quality in ('hq720.jpg', 'sddefault.jpg', 'hqdefault.jpg'):
+        url = f"https://i.ytimg.com/vi/{video_id}/{quality}"
         try:
             image = util.fetch_url(url, report_text="Saved thumbnail: " + video_id)
+            break
+        except util.FetchError as e:
+            if '404' in str(e):
+                continue
+            print("Failed to download thumbnail for " + video_id + ": " + str(e))
+            flask.abort(500)
         except urllib.error.HTTPError as e:
+            if e.code == 404:
+                continue
             print("Failed to download thumbnail for " + video_id + ": " + str(e))
             flask.abort(e.code)
+
+    if image is None:
+        flask.abort(404)
+
     try:
         f = open(thumbnail_path, 'wb')
     except FileNotFoundError:

youtube/util.py

@@ -542,11 +542,19 @@ class RateLimitedQueue(gevent.queue.Queue):
 
 
 def download_thumbnail(save_directory, video_id):
-    url = f"https://i.ytimg.com/vi/{video_id}/hq720.jpg"
     save_location = os.path.join(save_directory, video_id + ".jpg")
+    for quality in ('hq720.jpg', 'sddefault.jpg', 'hqdefault.jpg'):
+        url = f"https://i.ytimg.com/vi/{video_id}/{quality}"
         try:
             thumbnail = fetch_url(url, report_text="Saved thumbnail: " + video_id)
+        except FetchError as e:
+            if '404' in str(e):
+                continue
+            print("Failed to download thumbnail for " + video_id + ": " + str(e))
+            return False
         except urllib.error.HTTPError as e:
+            if e.code == 404:
+                continue
             print("Failed to download thumbnail for " + video_id + ": " + str(e))
             return False
         try:
@@ -557,6 +565,8 @@ def download_thumbnail(save_directory, video_id):
         f.write(thumbnail)
         f.close()
         return True
+    print("No thumbnail available for " + video_id)
+    return False
 
 
 def download_thumbnails(save_directory, ids):

youtube/watch.py

@@ -628,12 +628,12 @@ def get_watch_page(video_id=None):
 
     # prefix urls, and other post-processing not handled by yt_data_extract
     for item in info['related_videos']:
-        # For playlists, use first_video_id for thumbnail, not playlist id
+        # Only set thumbnail if YouTube didn't provide one
+        if not item.get('thumbnail'):
             if item.get('type') == 'playlist' and item.get('first_video_id'):
-            item['thumbnail'] = "https://i.ytimg.com/vi/{}/hq720.jpg".format(item['first_video_id'])
+                item['thumbnail'] = "https://i.ytimg.com/vi/{}/hqdefault.jpg".format(item['first_video_id'])
-        elif item.get('type') == 'video':
+            elif item.get('type') == 'video' and item.get('id'):
-            item['thumbnail'] = "https://i.ytimg.com/vi/{}/hq720.jpg".format(item['id'])
+                item['thumbnail'] = "https://i.ytimg.com/vi/{}/hqdefault.jpg".format(item['id'])
-        # For other types, keep existing thumbnail or skip
         util.prefix_urls(item)
         util.add_extra_html_info(item)
     for song in info['music_list']:
@@ -641,9 +641,9 @@ def get_watch_page(video_id=None):
     if info['playlist']:
         playlist_id = info['playlist']['id']
         for item in info['playlist']['items']:
-            # Set high quality thumbnail for playlist videos
+            # Only set thumbnail if YouTube didn't provide one
-            if item.get('type') == 'video' and item.get('id'):
+            if not item.get('thumbnail') and item.get('type') == 'video' and item.get('id'):
-                item['thumbnail'] = "https://i.ytimg.com/vi/{}/hq720.jpg".format(item['id'])
+                item['thumbnail'] = "https://i.ytimg.com/vi/{}/hqdefault.jpg".format(item['id'])
             util.prefix_urls(item)
             util.add_extra_html_info(item)
             if playlist_id:

youtube/yt_data_extract/common.py

@@ -369,9 +369,9 @@ def extract_item_info(item, additional_info={}):
         ['detailedMetadataSnippets', 0, 'snippetText'],
     ))
     info['thumbnail'] = normalize_url(multi_deep_get(item,
-        ['thumbnail', 'thumbnails', 0, 'url'],      # videos
+        ['thumbnail', 'thumbnails', -1, 'url'],      # videos (highest quality)
-        ['thumbnails', 0, 'thumbnails', 0, 'url'],  # playlists
+        ['thumbnails', 0, 'thumbnails', -1, 'url'],  # playlists
-        ['thumbnailRenderer', 'showCustomThumbnailRenderer', 'thumbnail', 'thumbnails', 0, 'url'], # shows
+        ['thumbnailRenderer', 'showCustomThumbnailRenderer', 'thumbnail', 'thumbnails', -1, 'url'], # shows
     ))
 
     info['badges'] = []

youtube/yt_data_extract/everything_else.py

@@ -229,7 +229,7 @@ def extract_playlist_metadata(polymer_json):
     if metadata['first_video_id'] is None:
         metadata['thumbnail'] = None
     else:
-        metadata['thumbnail'] = f"https://i.ytimg.com/vi/{metadata['first_video_id']}/hq720.jpg"
+        metadata['thumbnail'] = f"https://i.ytimg.com/vi/{metadata['first_video_id']}/hqdefault.jpg"
 
     metadata['video_count'] = extract_int(header.get('numVideosText'))
     metadata['description'] = extract_str(header.get('descriptionText'), default='')