Clarify frame extraction scope in README

README.md

@@ -47,7 +47,9 @@ bash scripts/unpack_data.sh /path/to/data
 
 Several large archives are distributed as multi-part files to satisfy Hub file-size limits. `unpack_data.sh` detects these parts automatically and streams them into a single extraction pass.
 
-### 2. Extract frames for a selected benchmark JSON
+### 2. Extract frames
+
+To extract frames only for one or more selected benchmark JSON files:
 
 ```bash
 python scripts/extract_vlac2_release_frames.py \
@@ -56,7 +58,15 @@ python scripts/extract_vlac2_release_frames.py \
   --benchmark-json benchmark_style_all/test_expert_seen/video_progress_benchmark_file.json
 ```
 
-The frame extractor decodes only the episodes referenced by the provided benchmark JSON file(s), rather than scanning the full raw-data release.
+This decodes only the episodes referenced by the provided benchmark JSON file(s), rather than scanning the full raw-data release.
+
+If `--benchmark-json` is omitted, the extractor scans all benchmark JSON files under `benchmark_style_all/`, collects all referenced records, and extracts the corresponding `main_path` videos:
+
+```bash
+python scripts/extract_vlac2_release_frames.py \
+  --data-root /path/to/data \
+  --frames-root /path/to/data_extracted_frames
+```
 
 ### 3. Use the benchmark JSON files