fix(player): 修复竖滑上一集不自动播放

lib/pages/player/widgets/player_opening_frame.dart

@@ -8,25 +8,33 @@ import 'package:flutter/material.dart';
 import '../../../core/config/app_config.dart';
 import '../../../core/data/services/sprite_thumbnail_asset_loader.dart';
 import '../../../core/data/services/sprite_thumbnail_axis.dart';
+import '../../../core/theme/app_colors.dart';
+import '../../../core/widgets/remote_image.dart';
 import 'scrub_preview_card.dart';
 
-/// 无雪碧图地址时不垫帧，交还给纯黑底。
-Widget? playerOpeningFrame(String? thumbnailsUrl) {
+/// 封面立即可见，雪碧图首帧解码完成后再覆盖封面。
+Widget? playerOpeningFrame(String? thumbnailsUrl, {String? posterUrl}) {
   final url = thumbnailsUrl?.trim() ?? '';
-  if (url.isEmpty) return null;
-  return PlayerOpeningFrame(thumbnailsUrl: url);
+  final poster = posterUrl?.trim() ?? '';
+  if (url.isEmpty && poster.isEmpty) return null;
+  return PlayerOpeningFrame(
+    thumbnailsUrl: url.isEmpty ? null : url,
+    posterUrl: poster.isEmpty ? null : poster,
+  );
 }
 
-/// 解码出视频画面前，用本集雪碧图第一帧垫底。
+/// 视频解码前依次使用封面和雪碧图首帧，最终由父层黑色兜底。
 class PlayerOpeningFrame extends StatefulWidget {
   const PlayerOpeningFrame({
     super.key,
-    required this.thumbnailsUrl,
+    this.thumbnailsUrl,
+    this.posterUrl,
     this.loader,
     this.cache,
   });
 
-  final String thumbnailsUrl;
+  final String? thumbnailsUrl;
+  final String? posterUrl;
   final SpriteThumbnailAssetLoader? loader;
   final OpeningFrameCache? cache;
 
@@ -55,8 +63,10 @@ class _PlayerOpeningFrameState extends State<PlayerOpeningFrame> {
 
   Future<void> _load() async {
     final serial = ++_serial;
+    final thumbnailsUrl = widget.thumbnailsUrl;
+    if (thumbnailsUrl == null) return;
     final frame = await (widget.cache ?? OpeningFrameCache.shared).load(
-      widget.thumbnailsUrl,
+      thumbnailsUrl,
       loader: widget.loader,
     );
     if (!mounted || serial != _serial) return;
@@ -66,11 +76,25 @@ class _PlayerOpeningFrameState extends State<PlayerOpeningFrame> {
   @override
   Widget build(BuildContext context) {
     final frame = _frame;
-    if (frame == null) return const SizedBox.expand();
-    return SpriteCropPreview(
-      key: const Key('player-opening-sprite'),
-      image: frame.image,
-      sourceRect: frame.sourceRect,
+    final posterUrl = widget.posterUrl;
+    return Stack(
+      fit: StackFit.expand,
+      children: [
+        const ColoredBox(color: AppColors.mediaBlack),
+        if (posterUrl != null)
+          RemoteImage(
+            posterUrl,
+            key: const Key('player-opening-poster'),
+            fit: BoxFit.cover,
+            fallbackColor: AppColors.mediaBlack,
+          ),
+        if (frame != null)
+          SpriteCropPreview(
+            key: const Key('player-opening-sprite'),
+            image: frame.image,
+            sourceRect: frame.sourceRect,
+          ),
+      ],
     );
   }
 }