fix(player): 使用高清首帧并稳定切集占位

test/playback/sprite_thumbnail_axis_test.dart

@@ -199,19 +199,26 @@ void main() {
       'title': 'episode',
       'isFree': true,
       'thumbnailsUrl': 'https://cdn.test/thumbnails.vtt?e=1&s=x',
+      'posterUrl': 'https://cdn.test/poster.jpg?e=1&s=x',
     });
     final ticket = PlayTicket.fromJson(const {
       'episodeId': '11',
       'accessible': true,
       'accessType': 'FREE',
       'thumbnailsUrl': 'https://cdn.test/thumbnails.vtt?e=1&s=x',
+      'posterUrl': 'https://cdn.test/poster.jpg?e=1&s=x',
     });
 
     expect(episode.thumbnailsUrl, ticket.thumbnailsUrl);
+    expect(episode.posterUrl, ticket.posterUrl);
     expect(
       episode.withVideoUrl('file:///video.mp4').thumbnailsUrl,
       episode.thumbnailsUrl,
     );
+    expect(
+      episode.withVideoUrl('file:///video.mp4').posterUrl,
+      episode.posterUrl,
+    );
   });
 }