perf(worker): 封面抽帧三优化 — blackdetect黑屏规避+单次ffmpeg批量抽帧+并发上传+CJK字体兜底

1. 黑屏检测（blackdetect）：抽帧前先用 ffmpeg blackdetect(d=0.3,pic_th=0.98,pix_th=0.10) 扫描成片黑屏区间，
   seek 点落在黑屏内时偏移到最近非黑屏位置；整段全黑则保留中点并打 warning 日志。避免封面/首帧落到黑屏。
2. 封面批量抽帧+并发上传：5次串行 ffmpeg -ss seek 改成单次 ffmpeg select between(t,...) 一次输出 5 帧；
   5帧上传 OSS 用 ThreadPoolExecutor 并发（max_workers=min(8,N)）。目标封面阶段从 ~3.1s 压到 <1.5s。
   单次 select 失败/命中不足自动回退到单帧 -ss seek 兜底，保证鲁棒性。
3. Worker Dockerfile 加 fonts-noto-cjk 安装与 fc-cache：
   - 在 worker.Dockerfile apt-get install 显式加 fonts-noto-cjk + fontconfig（base 镜像漂移兜底）
   - build 时 fc-cache -fv + fc-match 'Noto Sans CJK SC' 校验，确保 fc-match 能解析到 Noto，
     不再依赖 PIL 直读 ttf 兜底路径。

apps/worker/video_processing/thumbnail_generator.py

@@ -1,7 +1,10 @@
 """视频封面抽帧工具 — 从视频中抽取帧作为封面，支持标题文字叠加。
 
-统一封面管道（P1 优化后默认本地路径）：
-- 默认路径：本地 ffmpeg -ss 单帧 seek 抽取 + cv2 质量评分（清晰度/亮度/色彩），1-2s 完成
+封面管道（P2 优化后）：
+- 黑屏检测：ffmpeg blackdetect 扫描黑屏区间，抽帧点自动避开黑屏
+- 单次 ffmpeg select 抽多帧：一次 ffmpeg 进程用 select 滤镜输出 5 帧，避免 5 次起停进程
+- 并发上传：5 帧用 ThreadPoolExecutor 并行上传 OSS，目标封面阶段 <1.5s
+- 质量评分：cv2 清晰度/亮度/色彩三维评分选最佳帧
 - 可选 MediaKit 路径：配置 MEDIAKIT_COVER_ENABLED=true 时启用火山 MediaKit SceneChange 抽帧
 - 从已渲染视频抽帧：标题已通过 ASS 字幕烧进视频，帧天然带标题，无需再叠加。
 - 从源素材抽帧（API E2 兜底）：源素材无标题，通过 Pillow 在帧上绘制标题文字。
@@ -10,7 +13,9 @@
 from __future__ import annotations
 
 import logging
+import re
 import tempfile
+from concurrent.futures import ThreadPoolExecutor, as_completed
 from pathlib import Path
 from typing import Optional
 
@@ -173,6 +178,225 @@ def generate_and_upload_thumbnail(
         Path(tmp.name).unlink(missing_ok=True)
 
 
+def _detect_black_intervals(
+    video_path: str,
+    duration: float,
+    *,
+    black_min_duration: float = 0.3,
+    picture_black_ratio_th: float = 0.98,
+    pixel_black_th: float = 0.10,
+    timeout: int = 30,
+) -> list[tuple[float, float]]:
+    """用 ffmpeg blackdetect 扫描黑屏区间，返回 [(start, end), ...]。"""
+    from video_processing.ffmpeg_utils import FFMPEG_BIN, run_ffmpeg
+
+    if duration <= 0:
+        return []
+    cmd = [
+        FFMPEG_BIN,
+        "-nostdin",
+        "-i",
+        video_path,
+        "-vf",
+        (f"blackdetect=d={black_min_duration:.2f}:pic_th={picture_black_ratio_th:.2f}:pix_th={pixel_black_th:.2f}"),
+        "-an",
+        "-f",
+        "null",
+        "-",
+    ]
+    try:
+        _, stderr = run_ffmpeg(cmd, capture_output=True, timeout=timeout)
+    except Exception as e:
+        logger.warning("[thumbnail] blackdetect 失败，忽略黑屏规避: %s", e)
+        return []
+
+    intervals: list[tuple[float, float]] = []
+    pattern = re.compile(
+        r"black_start:(\d+(?:\.\d+)?)\s+black_end:(\d+(?:\.\d+)?)\s+black_duration:(\d+(?:\.\d+)?)",
+    )
+    for m in pattern.finditer(stderr or ""):
+        try:
+            bs = float(m.group(1))
+            be = float(m.group(2))
+            intervals.append((bs, be))
+        except ValueError:
+            continue
+    intervals.sort()
+    if intervals:
+        logger.info("[thumbnail] blackdetect 发现 %d 段黑屏: %s", len(intervals), intervals[:5])
+    return intervals
+
+
+def _adjust_seek_points_avoid_black(
+    seek_points: list[float],
+    black_intervals: list[tuple[float, float]],
+    duration: float,
+    *,
+    tolerance: float = 0.25,
+) -> list[float]:
+    """把落在黑屏区间的 seek 点偏移到最近的非黑屏位置。
+
+    策略：
+    - 若点在黑屏内，先尝试向前偏移到黑屏起点 - tolerance，再尝试向后偏移到黑屏终点 + tolerance；
+    - 若整个视频全黑（偏移后 <0 或 >duration），保留原点但日志标记警告；
+    - 偏移后若点与已有点重合（误差 <0.3s），做微调去重。
+    """
+    if not black_intervals or not seek_points:
+        return list(seek_points)
+
+    def in_black(t: float) -> tuple[float, float] | None:
+        for bs, be in black_intervals:
+            if bs <= t <= be:
+                return (bs, be)
+        return None
+
+    adjusted: list[float] = []
+    for t in seek_points:
+        seg = in_black(t)
+        if seg is None:
+            adjusted.append(max(0.0, min(duration, t)))
+            continue
+        bs, be = seg
+        # 先尝试向前
+        forward_t = bs - tolerance
+        if forward_t >= 0.0 and in_black(forward_t) is None:
+            adjusted.append(forward_t)
+            continue
+        # 再尝试向后
+        backward_t = be + tolerance
+        if backward_t <= duration and in_black(backward_t) is None:
+            adjusted.append(backward_t)
+            continue
+        # 整段 clip 全黑？保留中点但标记
+        logger.warning(
+            "[thumbnail] seek 点 %.2fs 落在黑屏区间 [%.2f,%.2f] 且无法偏移，保留原位置（可能是全黑片段）",
+            t,
+            bs,
+            be,
+        )
+        adjusted.append(max(0.0, min(duration, t)))
+
+    # 去重：相邻点若 <0.3s 则拉开
+    adjusted.sort()
+    deduped: list[float] = []
+    for t in adjusted:
+        if not deduped or abs(t - deduped[-1]) >= 0.3:
+            deduped.append(t)
+        else:
+            # 往后挪 0.5s
+            nt = t + 0.5
+            if nt <= duration and in_black(nt) is None:
+                deduped.append(nt)
+            else:
+                deduped.append(t)
+    return [round(max(0.0, min(duration, t)), 3) for t in deduped[: len(seek_points)]]
+
+
+def _extract_frames_single_pass(
+    video_path: str,
+    seek_points: list[float],
+    out_dir: str,
+    *,
+    prefix: str = "frame",
+    width: int = -1,
+    height: int = -1,
+    q: int = 2,
+    timeout: int = 30,
+) -> list[tuple[float, str]]:
+    """单次 ffmpeg 用 select 滤镜抽出 seek_points 对应的多帧。
+
+    ffmpeg -i input -vf "select='between(t,t1-0.03,t1+0.03)+between(t,t2-0.03,t2+0.03)+...',scale=...,format=yuvj420p"
+           -vsync vfr -q:v 2 out_dir/prefix_%02d.jpg
+
+    返回 [(seek_t, output_path), ...]，按输出帧序号升序。若输出帧数 < seek_points 数量，
+    不足部分用 extract_first_frame 兜底（保证返回数量 == len(seek_points)）。
+    """
+    from video_processing.ffmpeg_utils import FFMPEG_BIN, run_ffmpeg
+
+    out_dir_p = Path(out_dir)
+    out_dir_p.mkdir(parents=True, exist_ok=True)
+
+    # 构造 select 表达式：每个 seek 点用 ±30ms 窗口命中
+    # between(t, a, b) 返回 1 表示 t 在 [a,b] 内；多个 between 相加即为"任一命中"
+    select_terms = []
+    for t in seek_points:
+        a = max(0.0, t - 0.03)
+        b = t + 0.04
+        select_terms.append(f"between(t,{a:.3f},{b:.3f})")
+    select_expr = "+".join(select_terms)
+
+    if width > 0 or height > 0:
+        w_str = str(width) if width > 0 else "-1"
+        h_str = str(height) if height > 0 else "-1"
+        scale_filter = f"scale={w_str}:{h_str}:force_original_aspect_ratio=decrease"
+        vf = f"select='{select_expr}',{scale_filter},format=yuvj420p"
+    else:
+        vf = f"select='{select_expr}',format=yuvj420p"
+
+    out_pattern = str(out_dir_p / f"{prefix}_%02d.jpg")
+    cmd = [
+        FFMPEG_BIN,
+        "-y",
+        "-i",
+        video_path,
+        "-vf",
+        vf,
+        "-vsync",
+        "vfr",
+        "-q:v",
+        str(q),
+        out_pattern,
+    ]
+
+    results: list[tuple[float, str]] = []
+    single_pass_ok = False
+    try:
+        run_ffmpeg(cmd, capture_output=True, timeout=timeout)
+        # 读取输出文件
+        for i in range(1, len(seek_points) + 1):
+            fp = out_dir_p / f"{prefix}_{i:02d}.jpg"
+            if fp.exists() and fp.stat().st_size > 0:
+                results.append((seek_points[i - 1] if i - 1 < len(seek_points) else 0.0, str(fp)))
+        if len(results) >= len(seek_points):
+            single_pass_ok = True
+        else:
+            logger.warning(
+                "[thumbnail] 单次 ffmpeg 抽帧仅命中 %d/%d 帧，不足部分用单帧 seek 兜底",
+                len(results),
+                len(seek_points),
+            )
+    except Exception as e:
+        logger.warning("[thumbnail] 单次 ffmpeg select 抽帧失败，回退到单帧 seek: %s", e)
+
+    # 兜底：对缺失/失败的帧用 extract_first_frame 补抽
+    if not single_pass_ok:
+        # 清理不完整结果
+        for _, fp in results:
+            try:
+                Path(fp).unlink(missing_ok=True)
+            except Exception:
+                pass
+        results = []
+        for i, st in enumerate(seek_points):
+            fp = out_dir_p / f"{prefix}_fallback_{i:02d}.jpg"
+            try:
+                extract_first_frame(
+                    video_path,
+                    output_path=str(fp),
+                    seek_seconds=st,
+                    min_seek_seconds=0.5,
+                    timeout=timeout,
+                )
+                if fp.exists() and fp.stat().st_size > 0:
+                    results.append((st, str(fp)))
+                else:
+                    logger.warning("[thumbnail] 兜底单帧抽帧也失败 idx=%d t=%.2f", i, st)
+            except Exception as e:
+                logger.warning("[thumbnail] 兜底单帧抽帧异常 idx=%d t=%.2f: %s", i, st, e)
+
+    return results[: len(seek_points)]
+
+
 def _compute_clip_boundary_seek_points(
     duration: float,
     clip_boundaries: Optional[list[tuple[float, float]]] = None,
@@ -310,10 +534,11 @@ def extract_and_upload_cover_frames(
 ) -> list[dict]:
     """从视频中抽取多帧作为封面候选，通过质量评分选出最佳帧，上传到 OSS。
 
-    默认路径（P1优化）：本地 ffmpeg 单帧 seek 抽帧 + cv2 评分，预期 <2s 完成。
-    - 基于 clip 分段边界取各段中间帧（clip_boundaries 参数），效果优于均匀抽帧
-    - 无边界信息时均匀分布（10%~90% 之间）
-    - 所有帧本地 cv2 清晰度/亮度/色彩三维评分，最高分自动选出
+    P2 优化：
+    - 先用 ffmpeg blackdetect 扫描黑屏区间，seek 点自动避开黑屏
+    - 单次 ffmpeg select 抽 num_frames 帧（避免 5 次起停 ffmpeg 进程）
+    - 多帧 OSS 上传用 ThreadPoolExecutor 并发，目标封面阶段 <1.5s
+    - cv2 清晰度/亮度/色彩三维评分选最佳帧
 
     Fallback（MEDIAKIT_COVER_ENABLED=true）：火山 MediaKit SceneChange 抽帧（~60-90s）。
 
@@ -381,46 +606,81 @@ def extract_and_upload_cover_frames(
                 if len(candidates) >= num_frames:
                     logger.info("[thumbnail] MediaKit 抽帧完成: %d 帧", len(candidates))
 
-        # ── 默认路径：本地 ffmpeg 单帧 seek ───────────────────────────
+        # ── 默认路径：本地 ffmpeg 单次 select 抽帧 + 并发上传 ──────────────
         if len(candidates) < num_frames:
             if candidates:
                 logger.info("[thumbnail] MediaKit 不足 %d 帧，本地 ffmpeg 补充", num_frames)
             else:
-                logger.info("[thumbnail] 使用本地 ffmpeg 抽帧（num=%d, duration=%.1fs）", num_frames, duration)
+                logger.info(
+                    "[thumbnail] 使用本地 ffmpeg 抽帧（num=%d, duration=%.1fs）",
+                    num_frames,
+                    duration,
+                )
 
+            # 1) 计算 seek 点
             seek_points = _compute_clip_boundary_seek_points(duration, clip_boundaries, num_frames)
 
-            for i, seek_t in enumerate(seek_points):
-                tmp = tempfile.NamedTemporaryFile(suffix=".jpg", delete=False)
-                tmp.close()
-                _temp_paths.append(tmp.name)
-                try:
-                    frame_path = extract_first_frame(
-                        video_path,
-                        output_path=tmp.name,
-                        seek_seconds=seek_t,
-                        min_seek_seconds=0.5,
-                    )
+            # 2) 黑屏检测 + 偏移 seek 点
+            black_intervals = _detect_black_intervals(video_path, duration) if duration > 0 else []
+            if black_intervals:
+                seek_points = _adjust_seek_points_avoid_black(seek_points, black_intervals, duration)
+                logger.info("[thumbnail] 黑屏规避后 seek 点: %s", seek_points)
+
+            # 3) 单次 ffmpeg select 抽出所有帧（带失败兜底到单帧 seek）
+            with tempfile.TemporaryDirectory(prefix="thumb_") as frame_dir:
+                t1 = time.monotonic()
+                frame_results = _extract_frames_single_pass(
+                    video_path,
+                    seek_points,
+                    frame_dir,
+                    prefix="frame",
+                )
+                logger.info("[thumbnail] 抽帧耗时: %.2fs (%d 帧)", time.monotonic() - t1, len(frame_results))
+
+                # 4) 标题叠加（本地，CPU 很快）
+                for _st, fp in frame_results:
                     if title_text and title_text.strip():
-                        apply_title_overlay(
-                            frame_path,
-                            title_text,
-                            color=title_color,
-                            position=title_position,
-                            font_size=title_font_size,
-                        )
-                    storage_key = f"covers/{plan_id}/{task_id}/frame_{i}.jpg"
-                    url = upload_to_oss(frame_path, storage_key)
-                    if url:
-                        candidates.append(
-                            {
-                                "url": url,
-                                "position": seek_t,
-                                "image_path": tmp.name,
-                            }
-                        )
-                except Exception as e:
-                    logger.warning("[thumbnail] 封面候选帧 %d 提取失败: %s", i, e)
+                        try:
+                            apply_title_overlay(
+                                fp,
+                                title_text,
+                                color=title_color,
+                                position=title_position,
+                                font_size=title_font_size,
+                            )
+                        except Exception as e:
+                            logger.warning("[thumbnail] 标题叠加失败 %s: %s", fp, e)
+
+                # 5) 并发上传 OSS（线程池并发）
+                t2 = time.monotonic()
+
+                def _upload_one(idx: int, st: float, fp: str) -> dict | None:
+                    try:
+                        storage_key = f"covers/{plan_id}/{task_id}/frame_{idx}.jpg"
+                        url = upload_to_oss(fp, storage_key)
+                        if url:
+                            return {"url": url, "position": st, "image_path": fp}
+                        logger.warning("[thumbnail] 上传失败 idx=%d", idx)
+                    except Exception as e:
+                        logger.warning("[thumbnail] 上传异常 idx=%d t=%.2f: %s", idx, st, e)
+                    return None
+
+                upload_results: list[dict | None] = [None] * len(frame_results)
+                max_workers = min(8, max(2, len(frame_results)))
+                with ThreadPoolExecutor(max_workers=max_workers) as pool:
+                    future_map = {pool.submit(_upload_one, i, st, fp): i for i, (st, fp) in enumerate(frame_results)}
+                    for fut in as_completed(future_map):
+                        i = future_map[fut]
+                        try:
+                            upload_results[i] = fut.result()
+                        except Exception as e:
+                            logger.warning("[thumbnail] 上传 feature 异常 idx=%d: %s", i, e)
+                logger.info("[thumbnail] 并发上传耗时: %.2fs", time.monotonic() - t2)
+
+                for r in upload_results:
+                    if r is not None:
+                        _temp_paths.append(r["image_path"])
+                        candidates.append(r)
 
         # ── 阶段 2：质量评分 ────────────────────────────────────────────
         if len(candidates) > 1:

infra/docker/worker.Dockerfile

@@ -10,6 +10,20 @@ FROM xiaoxia-registry.cn-hangzhou.cr.aliyuncs.com/xiaoxiakeji/saas-worker-base:l
 # 构建参数：版本号（CI 传入 commit hash）
 ARG APP_VERSION=dev
 
+# 使用阿里云镜像加速
+RUN sed -i 's|deb.debian.org|mirrors.aliyun.com|g' /etc/apt/sources.list.d/debian.sources 2>/dev/null || \
+    sed -i 's|deb.debian.org|mirrors.aliyun.com|g' /etc/apt/sources.list 2>/dev/null || true
+
+# CJK 字体保障：确保 fonts-noto-cjk 已安装（base 镜像漂移兜底）+ 重建字体缓存
+# 验证 fc-match 能正确解析 Noto Sans CJK SC，避免 PIL 直读 ttf 兜底
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    fonts-noto-cjk \
+    fontconfig \
+    && rm -rf /var/lib/apt/lists/* \
+    && fc-cache -fv \
+    && fc-match 'Noto Sans CJK SC' | grep -qi 'noto' \
+    && echo "[font] fc-match Noto Sans CJK SC: $(fc-match 'Noto Sans CJK SC' | head -1)"
+
 # 创建非 root 用户
 RUN groupadd -r celery \
     && useradd -r -g celery -d /app -s /sbin/nologin celery \