[ie/bigo] Support --wait-for-video (#15463)

Authored by: olipfei

yt_dlp/extractor/bigo.py

@@ -1,5 +1,5 @@
 from .common import InfoExtractor
-from ..utils import ExtractorError, urlencode_postdata
+from ..utils import ExtractorError, UserNotLive, urlencode_postdata
 
 
 class BigoIE(InfoExtractor):
@@ -40,7 +40,7 @@ class BigoIE(InfoExtractor):
         info = info_raw.get('data') or {}
 
         if not info.get('alive'):
-            raise ExtractorError('This user is offline.', expected=True)
+            raise UserNotLive(video_id=user_id)
 
         formats, subs = self._extract_m3u8_formats_and_subtitles(
             info.get('hls_src'), user_id, 'mp4', 'm3u8')

yt_dlp/extractor/twitch.py

@@ -680,6 +680,10 @@ class TwitchPlaylistBaseIE(TwitchBaseIE):
                 }],
                 f'Downloading {self._NODE_KIND}s GraphQL page {page_num}',
                 fatal=False)
+            # Avoid extracting random/unrelated entries when channel_name doesn't exist
+            # See https://github.com/yt-dlp/yt-dlp/issues/15450
+            if traverse_obj(page, (0, 'data', 'user', 'id', {str})) == '':
+                raise ExtractorError(f'Channel "{channel_name}" not found', expected=True)
             if not page:
                 break
             edges = try_get(