fix(P0): unified横屏pad取整+错误日志增强+legacy导入+素材created_at (#522)

Co-authored-by: xiaoxia <dev@xiaoxiajianji.com>
Co-committed-by: xiaoxia <dev@xiaoxiajianji.com>

apps/worker/video_processing/unified_render_service.py

@@ -1008,7 +1008,7 @@ class UnifiedRenderService:
         else:
             # main / broll: 等比缩放 + 居中留黑边（保持原始比例，不裁剪内容）
             filters.append(f"scale={self.output_width}:{self.output_height}" ":force_original_aspect_ratio=decrease")
-            filters.append(f"pad={self.output_width}:{self.output_height}:(ow-iw)/2:(oh-ih)/2:black")
+            filters.append(f"pad={self.output_width}:{self.output_height}:trunc((ow-iw)/2):trunc((oh-ih)/2):black")
 
         # 调色滤镜
         color_grade = ColorGradeConfig.from_dict(clip.config.get("color_grade"))
@@ -1112,12 +1112,15 @@ class UnifiedRenderService:
         try:
             run_ffmpeg(command)
         except subprocess.CalledProcessError as e:
+            stderr_text = (e.stderr or "").strip()
+            stderr_tail = stderr_text[-1500:] if len(stderr_text) > 1500 else stderr_text
             logger.error(
-                "直通渲染失败: plan_id=%s clip=%s exit_code=%d\nvf=%s",
+                "直通渲染失败: plan_id=%s clip=%s exit_code=%d\nvf=%s\nstderr(last 1500):\n%s",
                 self.plan.id,
                 clip.clip_id,
                 e.returncode,
                 vf_str[:2000],
+                stderr_tail,
             )
             raise
 
@@ -1342,7 +1345,7 @@ class UnifiedRenderService:
                 filters.append(
                     f"scale={self.output_width}:{self.output_height}" ":force_original_aspect_ratio=decrease"
                 )
-                filters.append(f"pad={self.output_width}:{self.output_height}:(ow-iw)/2:(oh-ih)/2:black")
+                filters.append(f"pad={self.output_width}:{self.output_height}:trunc((ow-iw)/2):trunc((oh-ih)/2):black")
 
             # 调色滤镜（每个 clip 独立的 color grade 配置）
             color_grade = ColorGradeConfig.from_dict(clip.config.get("color_grade"))
@@ -1576,12 +1579,15 @@ class UnifiedRenderService:
         try:
             run_ffmpeg(command)
         except subprocess.CalledProcessError as e:
-            # 额外记录 filter_complex，方便排查滤镜链构建问题
+            # 额外记录 filter_complex + stderr，方便排查滤镜链构建问题
+            stderr_text = (e.stderr or "").strip()
+            stderr_tail = stderr_text[-1500:] if len(stderr_text) > 1500 else stderr_text
             logger.error(
-                "渲染失败: plan_id=%s exit_code=%d\nfilter_complex:\n%s",
+                "渲染失败: plan_id=%s exit_code=%d\nfilter_complex:\n%s\nstderr(last 1500):\n%s",
                 self.plan.id,
                 e.returncode,
                 filter_complex[:5000],
+                stderr_tail,
             )
             raise