feat: 上传时自动检测 HEVC 编码并转码为 1080p H.264

解决 4K HEVC 素材在浏览器 WebCodecs 硬件解码时输出黑帧的问题。

改动范围：仅 ingest.py（+88 行）
- metadata 提取后检测 codec 是否为 hevc/h265/hvh1
- HEVC 素材自动转码：H.264 CRF18 + 1080p + yuv420p + faststart
- 转码产物上传 OSS，storage_key 指向 _h264.mp4
- 转码后重新提取 metadata（新 codec/size/分辨率）
- 非 HEVC 素材（H.264 等）不做任何处理
- 转码失败降级使用原始文件，不阻塞上传流程
- 超时 300s，临时文件 finally 清理

apps/worker/worker_app/tasks/ingest.py

@@ -233,6 +233,94 @@ def ingest_asset(job_id: str) -> dict:
                         job_id,
                         thumb_err,
                     )
+
+            # ── HEVC 自动转码为 1080p H.264 ──────────────────────────────
+            # 浏览器 WebCodecs 硬件解码 HEVC 输出黑帧，上传时自动转码
+            # 失败时降级使用原始文件，不阻塞上传流程
+            if (
+                media_type == "video"
+                and extract_success
+                and local_file
+                and local_file.exists()
+            ):
+                codec = (metadata.get("codec") or "").lower()
+                if codec in ("hevc", "h265", "hvh1"):
+                    logger.info(
+                        "检测到 HEVC 编码 (codec=%s)，启动转码: job_id=%s",
+                        codec, job_id,
+                    )
+                    _tc_tmp = None
+                    try:
+                        _tc_tmp = Path(tempfile.mktemp(suffix="_h264.mp4"))
+                        _cmd = [
+                            "ffmpeg", "-y",
+                            "-i", str(local_file),
+                            "-c:v", "libx264",
+                            "-preset", "fast",
+                            "-crf", "18",
+                            "-vf",
+                            "scale='if(gt(ih,1080),-2,iw)':'if(gt(ih,1080),1080,ih)'",
+                            "-pix_fmt", "yuv420p",
+                            "-c:a", "aac",
+                            "-b:a", "128k",
+                            "-movflags", "+faststart",
+                            str(_tc_tmp),
+                        ]
+                        _proc = subprocess.run(
+                            _cmd, capture_output=True, text=True, timeout=300,
+                        )
+                        if (
+                            _proc.returncode == 0
+                            and _tc_tmp.exists()
+                            and _tc_tmp.stat().st_size > 0
+                        ):
+                            from video_processing.oss_helpers import upload_to_oss
+
+                            _p = Path(job.storage_key)
+                            _new_key = str(
+                                _p.parent / (_p.stem + "_h264" + _p.suffix)
+                            )
+                            _url = upload_to_oss(_tc_tmp, _new_key)
+                            if _url:
+                                job.storage_key = _new_key
+                                metadata, extract_success = (
+                                    extract_media_metadata(
+                                        str(_tc_tmp), media_type,
+                                    )
+                                )
+                                logger.info(
+                                    "HEVC→H.264 转码完成: job_id=%s key=%s",
+                                    job_id, _new_key[:80],
+                                )
+                            else:
+                                logger.warning(
+                                    "转码文件上传 OSS 失败，使用原始文件: job_id=%s",
+                                    job_id,
+                                )
+                        else:
+                            _tail = (
+                                _proc.stderr[-300:] if _proc.stderr else ""
+                            )
+                            logger.warning(
+                                "FFmpeg 转码失败 rc=%s，降级原始文件: job_id=%s",
+                                _proc.returncode, job_id,
+                            )
+                    except subprocess.TimeoutExpired:
+                        logger.warning(
+                            "FFmpeg 转码超时 (300s)，降级原始文件: job_id=%s",
+                            job_id,
+                        )
+                    except Exception as _e:
+                        logger.warning(
+                            "HEVC 转码异常（降级原始文件）: job_id=%s err=%s",
+                            job_id, _e,
+                        )
+                    finally:
+                        if _tc_tmp and _tc_tmp.exists():
+                            try:
+                                _tc_tmp.unlink()
+                            except OSError:
+                                pass
         finally:
             if local_file and local_file.exists():
                 try: