feat: adaptive keyframe count based on video duration

- Replace fixed 5-8 keyframe limit with duration-based adaptive sizing
- Candidate frames: clamp(duration_min × 2, 30, 120)
- Keyframe cap: clamp(duration / 150s, 8, 30)
- 30min video → 12 keyframes (was 8), 60min → 24, 120min → 30
- Short videos (<12min) still get floor of 8 keyframes
- Add Ollama keep-alive config doc to PROGRESS.md (OLLAMA_KEEP_ALIVE=-1)
- Update config.yaml and config.yaml.example with new video params

fam-edge/config/config.yaml

@@ -13,11 +13,15 @@ server:
   port: 5000
   max_concurrent_tasks: 1
 
-# 关键帧筛选参数
+# 关键帧筛选参数（自适应：帧数随视频时长动态计算）
 video:
-  candidate_frames: 30
-  min_key_frames: 5
-  max_key_frames: 8
+  candidate_per_minute: 2      # 每分钟粗抽候选帧数
+  candidate_min: 30            # 候选帧下限（短视频保底）
+  candidate_max: 120           # 候选帧上限（超长视频截断）
+  key_frame_interval_sec: 150  # 关键帧间隔（秒），每2.5分钟1张
+  min_key_frames: 5            # 关键帧下限（帧差不足时补足到此数）
+  max_key_frames_floor: 8      # 关键帧上限的下限（短视频保底）
+  max_key_frames_cap: 30       # 关键帧上限（超长视频截断）
   mse_threshold: 500
   jpeg_quality: 80
   max_long_edge: 1024