Document custom frame output root

README.md

@@ -50,18 +50,14 @@ bash scripts/extract_vlac2_release_raw_archives.sh /path/to/data
 ### 2. Extract frames
 
 ```bash
-python scripts/extract_vlac2_release_frames.py --data-root /path/to/data
+python scripts/extract_vlac2_release_frames.py \
+  --data-root /path/to/data \
+  --frames-root /path/to/data_extracted_frames
 ```
 
-This command reads raw videos from `/path/to/data` and writes extracted frames to `_extracted_frames/` under the release directory. The output location is fixed by the release package and does not need to be specified explicitly. Only the benchmark-designated main camera stream is materialized.
+This command reads raw videos from `/path/to/data` and writes extracted frames to `/path/to/data_extracted_frames`. Only the benchmark-designated main camera stream is materialized.
 
-For example, if the release directory is:
-
-```text
-/path/to/release
-```
-
-and the raw videos are unpacked to:
+For example, if the raw videos are unpacked to:
 
 ```text
 /path/to/release/data
@@ -70,9 +66,11 @@ and the raw videos are unpacked to:
 then the extracted frames will be written to:
 
 ```text
-/path/to/release/_extracted_frames
+/path/to/release/data_extracted_frames
 ```
 
+If `--frames-root` is omitted, frames are written to `_extracted_frames/` under the release directory by default.
+
 ### 3. Use the benchmark splits
 
 The benchmark JSON files are pre-generated and can be used directly. No benchmark reconstruction is required.
@@ -88,7 +86,7 @@ Replace `__VLAC2_FRAMES_ROOT__` with the absolute path to the extracted-frame di
 For example, if frames are extracted to:
 
 ```text
-/path/to/release/_extracted_frames
+/path/to/release/data_extracted_frames
 ```
 
 then:
@@ -100,7 +98,7 @@ __VLAC2_FRAMES_ROOT__/...
 should be resolved as:
 
 ```text
-/path/to/release/_extracted_frames/...
+/path/to/release/data_extracted_frames/...
 ```
 
 ## Notes