# Loading

## Hugging Face metadata

```python
from datasets import load_dataset

repo = "deepdeltalab/CausalCascade"
rq2 = load_dataset(repo, "rq2_pairs", split="test")
print(rq2.select_columns("counterfactual_reference_video_path")[0])
```

The `base_scenes` and `rq2_pairs` viewers display native `Image` and `Video`
columns. The `counterfactuals` viewer contains metadata and media paths.
Image bytes are
embedded in Parquet; video columns reference MP4 files in this repository
using `hf://datasets/deepdeltalab/CausalCascade@main/` URIs.
The separate `*_path` columns remain repository-relative strings.

To inspect metadata without decoding native media:

```python
rq2_metadata = rq2.remove_columns([
    "factual_initial_frame", "counterfactual_initial_frame",
    "factual_reference_video", "counterfactual_reference_video",
])
```

Native video decoding through `datasets` requires its compatible TorchCodec
dependencies. The wrapper below uses OpenCV and removes the viewer columns
before reading rows, so it retains its existing lazy-loading behavior.

## Lazy PyTorch loading

Clone the dataset repository and install its lightweight wrapper:

```bash
pip install -e ".[video]"
```

```python
from torch.utils.data import DataLoader
from causalcascade import CausalCascadeDataset, collate_fn

dataset = CausalCascadeDataset(
    repo_id="deepdeltalab/CausalCascade",
    subset="rq2_pairs",
    split="test",
    decode_images=True,
    decode_video=True,
    video_size=(480, 854),  # (height, width)
    video_frame_stride=2,
    load_annotations=True,
)

loader = DataLoader(dataset, batch_size=1, num_workers=4, collate_fn=collate_fn)
for batch in loader:
    factual_video = batch["factual_reference_video"]
    counterfactual_video = batch["counterfactual_reference_video"]
    break
```

Videos are decoded only inside `__getitem__`. `video_size`, `video_frame_stride`, and `video_max_frames` control memory use without changing the stored reference videos. Because videos may have different lengths, `collate_fn` stacks equal-shaped tensors and otherwise returns a list. Set `decode_video=False` to keep path strings without downloading videos.

The example's resizing and frame stride are loading conveniences, not the evaluation protocol. Use the complete stored rollouts and the companion metric code for official motion evaluation. For RQ2, use the matched Level 1 prompts and both factual/counterfactual references in each row; an edit instruction describes the intervention and is not a replacement generation prompt.

For a local checkout, replace `repo_id` with `local_root="/path/to/CausalCascade"`.