新增剪接點轉場: 畫面淡出淡入 + 聲音恆定功率交叉淡化

- 畫面用 FFmpeg xfade(預設 fadeblack 淡出到黑再淡入),逐段串接並正確計算 offset
- 聲音用 acrossfade 等功率曲線(c1=qsin:c2=qsin)= 恆定功率,與畫面同步重疊
- 開啟轉場會自動重新編碼;偵測到 NVIDIA 顯卡時用 h264_nvenc 硬體加速 4K
- 新增 config 參數: transition / transition_duration / video_transition
- 轉場長度自動夾到比最短片段小,避免 xfade 出錯;單一片段時免轉場直接無損切出
- 已實測 3 段 4K 片段串接,輸出時長與音畫同步皆正確;同步更新 README

本次調整由 Claude Opus 4.8 (1M context) 協助開發與處理。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -93,10 +93,18 @@ python auto_remove_redlight.py 01.MOV 03.MOV 05.MOV
 | `min_keep` | `0.8` | 保留片段短於此秒數即丟棄 |
 | `use_gpu` | `true` | 是否使用 GPU（無 CUDA 時自動退回 CPU） |
 | `reencode` | `false` | `false` = 無損快剪；`true` = 重新編碼，切點精準到幀但較慢 |
+| `transition` | `true` | 剪接點是否加轉場（淡出淡入 + 恆定功率交叉淡化）。**開啟會強制重新編碼**，有 NVIDIA 顯卡時自動用 NVENC 加速 |
+| `transition_duration` | `0.5` | 轉場長度（秒），畫面與聲音共用以維持同步 |
+| `video_transition` | `fadeblack` | 畫面轉場類型：`fadeblack`=淡出到黑再淡入；`fade`=交叉溶接；其餘見 FFmpeg `xfade` 文件 |
 | `base_dir` | `E:\\videos` | 影片根目錄 |
 
 > 參數優先順序：**命令列參數 > config.json > 程式內建預設**
 
+### 關於轉場與無損
+
+- `transition: false` → 使用 FFmpeg `-c copy` 串流複製，**畫質無損、速度快**，但剪接點是硬切。
+- `transition: true` → 在每個剪接點加上**畫面淡出淡入**（`xfade`）與**聲音恆定功率交叉淡化**（`acrossfade`，`c1=qsin:c2=qsin`）。此模式必須重新編碼（非無損），4K 影片較耗時，建議搭配 NVIDIA 顯卡用 NVENC 加速。
+
 ---
 
 ## 輸出結果

auto_remove_redlight.py

@@ -117,6 +117,17 @@ REENCODE        = False             # False = 無損 -c copy(切點對齊關鍵
 PROGRESS_EVERY  = 60                # 進度回報: 每處理幾秒影片印一行目前時速 (秒)。
                                     #   純顯示用,改小只是印多幾行,不影響速度與偵測精度
 
+# --- 剪接點轉場(淡出淡入 / 恆定功率交叉淡化)------------------
+# 注意: 一旦開啟轉場,就「必須重新編碼」(濾鏡無法用 -c copy),非無損且較慢。
+#       有 NVIDIA 顯卡時會自動用 NVENC 硬體編碼加速 4K。
+TRANSITION          = True          # 是否在每個剪接點加轉場。False = 維持無損快剪
+TRANSITION_DURATION = 0.5           # 轉場長度 (秒)。畫面與聲音共用同一長度,確保同步
+VIDEO_TRANSITION    = "fadeblack"   # 畫面轉場 (FFmpeg xfade 類型):
+                                    #   fadeblack = 淡出到黑再淡入(較接近「淡出淡入」)
+                                    #   fade      = 交叉溶接(兩段直接互溶)
+                                    #   其它如 dissolve, smoothleft... 見 ffmpeg xfade 文件
+                                    # 聲音固定用 acrossfade 等功率曲線(c1=qsin:c2=qsin)=恆定功率
+
 # --- 批次模式 -----------------------------------------------
 # 會被當成影片來處理的副檔名(小寫比較)
 VIDEO_EXTS = {".mov", ".mp4", ".m4v", ".avi", ".mkv", ".mts", ".m2ts", ".insv"}
@@ -465,6 +476,109 @@ def ffmpeg_cut_concat(input_path: str, keeps: List[Tuple[float, float]],
         shutil.rmtree(tmpdir, ignore_errors=True)  # 清掉暫存檔
 
 
+def has_audio(path: str) -> bool:
+    """用 ffprobe 判斷影片是否有音訊軌。出錯時保守假設『有』。"""
+    if shutil.which("ffprobe") is None:
+        return True
+    try:
+        out = subprocess.run(
+            ["ffprobe", "-v", "error", "-select_streams", "a",
+             "-show_entries", "stream=index", "-of", "csv=p=0", path],
+            capture_output=True, text=True)
+        return bool(out.stdout.strip())
+    except Exception:
+        return True
+
+
+def ffmpeg_cut_concat_xfade(input_path: str, keeps: List[Tuple[float, float]],
+                            output_path: str, use_gpu: bool,
+                            tmp_parent: Optional[str] = None) -> None:
+    """
+    把 keeps 各片段接起來,並在「每個剪接點」加上轉場:
+      - 畫面: xfade(VIDEO_TRANSITION,例如 fadeblack 淡出淡入)
+      - 聲音: acrossfade 等功率曲線(c1=qsin:c2=qsin)= 恆定功率交叉淡化
+    兩者重疊長度相同(TRANSITION_DURATION),因此畫面與聲音同步。
+
+    ※ 轉場需要重新編碼(濾鏡無法 -c copy)。有 NVIDIA 顯卡時用 h264_nvenc 硬體加速。
+    """
+    n = len(keeps)
+    durs = [e - s for (s, e) in keeps]
+
+    # 只有一段 → 沒有剪接點,不需轉場,直接無損切出
+    if n == 1:
+        s, e = keeps[0]
+        run_cmd(["ffmpeg", "-y", "-ss", f"{s:.3f}", "-t", f"{e - s:.3f}",
+                 "-i", input_path, "-c", "copy",
+                 "-avoid_negative_ts", "make_zero", output_path])
+        print(f"[INFO] 完成(單一片段,免轉場)! 輸出檔案: {output_path}")
+        return
+
+    # 轉場長度不能 >= 任何片段,否則 xfade/acrossfade 會出錯 → 夾到安全值
+    d = min(TRANSITION_DURATION, min(durs) - 0.1)
+    if d <= 0.05:
+        print("[WARN] 片段太短,改用無轉場拼接。")
+        ffmpeg_cut_concat(input_path, keeps, output_path, reencode=True,
+                          tmp_parent=tmp_parent)
+        return
+
+    audio = has_audio(input_path)
+
+    # 每個保留片段當成一個輸入(同一來源檔多次 -ss/-t 取段)
+    cmd: List[str] = ["ffmpeg", "-y"]
+    for (s, e) in keeps:
+        cmd += ["-ss", f"{s:.3f}", "-t", f"{e - s:.3f}", "-i", input_path]
+
+    # --- 組 filter_complex ---
+    parts: List[str] = []
+
+    # 畫面: 先把每段正規化(統一時間基準/格式),再逐段 xfade
+    for i in range(n):
+        parts.append(f"[{i}:v]settb=AVTB,format=yuv420p[v{i}]")
+    prev = "v0"
+    run_len = durs[0]
+    for j in range(1, n):
+        offset = run_len - d                      # 轉場在「目前累積長度 - d」處開始
+        out = f"vx{j}"
+        parts.append(
+            f"[{prev}][v{j}]xfade=transition={VIDEO_TRANSITION}:"
+            f"duration={d:.3f}:offset={offset:.3f}[{out}]")
+        prev = out
+        run_len = run_len + durs[j] - d           # xfade 後總長
+    vlabel = prev
+
+    # 聲音: 逐段 acrossfade(等功率 = 恆定功率)
+    alabel = None
+    if audio:
+        prev_a = "0:a"
+        for j in range(1, n):
+            out = f"ax{j}"
+            parts.append(
+                f"[{prev_a}][{j}:a]acrossfade=d={d:.3f}:c1=qsin:c2=qsin[{out}]")
+            prev_a = out
+        alabel = prev_a
+
+    filtergraph = ";".join(parts)
+
+    # --- 編碼器: 有 GPU 用 NVENC,否則 libx264 ---
+    if use_gpu:
+        venc = ["-c:v", "h264_nvenc", "-preset", "p5", "-cq", "19"]
+    else:
+        venc = ["-c:v", "libx264", "-preset", "medium", "-crf", "18"]
+
+    cmd += ["-filter_complex", filtergraph, "-map", f"[{vlabel}]"]
+    if audio:
+        cmd += ["-map", f"[{alabel}]", "-c:a", "aac", "-b:a", "256k"]
+    else:
+        cmd += ["-an"]
+    cmd += venc + ["-pix_fmt", "yuv420p", output_path]
+
+    print(f"    轉場拼接 {n} 段(轉場 {d:.2f}s,畫面={VIDEO_TRANSITION},"
+          f"聲音=恆定功率,編碼={'NVENC' if use_gpu else 'x264'})...")
+    print("    ※ 4K 重新編碼較久,請耐心等候。")
+    run_cmd(cmd)
+    print(f"[INFO] 完成! 輸出檔案: {output_path}")
+
+
 # ---------- preview: 輸出 ROI 預覽圖 ----------
 
 def save_preview(video_path: str, roi: Tuple[int, int, int, int],
@@ -761,9 +875,15 @@ def process_one(video_path: str, roi: Tuple[int, int, int, int],
         return {"file": stem, "status": "skipped_no_keep",
                 "removed": removed_total}
 
-    # 4. FFmpeg 無損切割 + 拼接(暫存放在輸出同顆硬碟)
+    # 4. FFmpeg 切割 + 拼接
-    ffmpeg_cut_concat(video_path, keeps, out_path, args.reencode,
+    if TRANSITION and len(keeps) >= 1:
-                      tmp_parent=out_dir)
+        # 有轉場: xfade 淡出淡入 + acrossfade 恆定功率(需重新編碼)
+        ffmpeg_cut_concat_xfade(video_path, keeps, out_path,
+                                use_gpu=args.gpu, tmp_parent=out_dir)
+    else:
+        # 無轉場: 維持無損快剪
+        ffmpeg_cut_concat(video_path, keeps, out_path, args.reencode,
+                          tmp_parent=out_dir)
     return {"file": stem, "status": "ok", "output": out_path,
             "removed": removed_total, "redlights": len(removals)}
 
@@ -787,6 +907,9 @@ _CONFIG_KEYS = {
     "min_keep":        "MIN_KEEP",
     "use_gpu":         "USE_GPU",
     "reencode":        "REENCODE",
+    "transition":         "TRANSITION",
+    "transition_duration": "TRANSITION_DURATION",
+    "video_transition":   "VIDEO_TRANSITION",
     "base_dir":        "BASE_DIR",
 }
 

config.json

@@ -17,5 +17,8 @@
   "min_keep": 0.8,
   "use_gpu": true,
   "reencode": false,
+  "transition": true,
+  "transition_duration": 0.5,
+  "video_transition": "fadeblack",
   "base_dir": "E:\\videos"
 }