diff --git a/examples/port_datasets/droid_rlds/slurm_aggregate_shards.py b/examples/port_datasets/droid_rlds/slurm_aggregate_shards.py
index d2f2dfdf..6d124097 100644
--- a/examples/port_datasets/droid_rlds/slurm_aggregate_shards.py
+++ b/examples/port_datasets/droid_rlds/slurm_aggregate_shards.py
@@ -26,7 +26,7 @@ from datatrove.pipeline.base import PipelineStep
 from examples.port_datasets.droid_rlds.port_droid import DROID_SHARDS
 from lerobot.common.datasets.aggregate import validate_all_metadata
 from lerobot.common.datasets.lerobot_dataset import LeRobotDatasetMetadata
-from lerobot.common.datasets.utils import write_episode, write_episode_stats, write_info, write_task
+from lerobot.common.datasets.utils import write_episode, legacy_write_episode_stats, write_info, legacy_write_task
 from lerobot.common.utils.utils import init_logging
 
 
@@ -124,11 +124,11 @@ class AggregateDatasets(PipelineStep):
         for episode_index, episode_stats in tqdm.tqdm(
             aggr_meta.episodes_stats.items(), desc="Write episodes stats"
         ):
-            write_episode_stats(episode_index, episode_stats, aggr_meta.root)
+            legacy_write_episode_stats(episode_index, episode_stats, aggr_meta.root)
 
         # create a new task jsonl with updated episode_index using write_task
         for task_index, task in tqdm.tqdm(aggr_meta.tasks.items(), desc="Write tasks"):
-            write_task(task_index, task, aggr_meta.root)
+            legacy_write_task(task_index, task, aggr_meta.root)
 
         write_info(aggr_meta.info, aggr_meta.root)
 
diff --git a/lerobot/common/datasets/aggregate.py b/lerobot/common/datasets/aggregate.py
index 8761def9..df74e767 100644
--- a/lerobot/common/datasets/aggregate.py
+++ b/lerobot/common/datasets/aggregate.py
@@ -5,7 +5,7 @@ import pandas as pd
 import tqdm
 
 from lerobot.common.datasets.lerobot_dataset import LeRobotDataset, LeRobotDatasetMetadata
-from lerobot.common.datasets.utils import write_episode, write_episode_stats, write_info, write_task
+from lerobot.common.datasets.utils import write_episode, legacy_write_episode_stats, write_info, legacy_write_task
 from lerobot.common.utils.utils import init_logging
 
 
@@ -136,11 +136,11 @@ def aggregate_datasets(repo_ids: list[str], aggr_repo_id: str, aggr_root=None):
 
     # create a new episode_stats jsonl with updated episode_index using write_episode_stats
     for episode_index, episode_stats in aggr_meta.episodes_stats.items():
-        write_episode_stats(episode_index, episode_stats, aggr_meta.root)
+        legacy_write_episode_stats(episode_index, episode_stats, aggr_meta.root)
 
     # create a new task jsonl with updated episode_index using write_task
     for task_index, task in aggr_meta.tasks.items():
-        write_task(task_index, task, aggr_meta.root)
+        legacy_write_task(task_index, task, aggr_meta.root)
 
     write_info(aggr_meta.info, aggr_meta.root)
 
diff --git a/lerobot/common/datasets/backward_compatibility.py b/lerobot/common/datasets/backward_compatibility.py
index d1b8926a..25678eed 100644
--- a/lerobot/common/datasets/backward_compatibility.py
+++ b/lerobot/common/datasets/backward_compatibility.py
@@ -33,6 +33,18 @@ If you encounter a problem, contact LeRobot maintainers on [Discord](https://dis
 or open an [issue on GitHub](https://github.com/huggingface/lerobot/issues/new/choose).
 """
 
+V30_MESSAGE = """
+The dataset you requested ({repo_id}) is in {version} format.
+While current version of LeRobot is backward-compatible with it, the version of your dataset still uses global
+stats instead of per-episode stats. Update your dataset stats to the new format using this command:
+```
+python lerobot/common/datasets/v30/convert_dataset_v21_to_v30.py --repo-id={repo_id}
+```
+
+If you encounter a problem, contact LeRobot maintainers on [Discord](https://discord.com/invite/s3KuuzsPFb)
+or open an [issue on GitHub](https://github.com/huggingface/lerobot/issues/new/choose).
+"""
+
 FUTURE_MESSAGE = """
 The dataset you requested ({repo_id}) is only available in {version} format.
 As we cannot ensure forward compatibility with it, please update your current version of lerobot.
@@ -44,7 +56,12 @@ class CompatibilityError(Exception): ...
 
 class BackwardCompatibilityError(CompatibilityError):
     def __init__(self, repo_id: str, version: packaging.version.Version):
-        message = V2_MESSAGE.format(repo_id=repo_id, version=version)
+        if version.major == 3:
+            message = V30_MESSAGE.format(repo_id=repo_id, version=version)
+        elif version.major == 2:
+            message = V2_MESSAGE.format(repo_id=repo_id, version=version)
+        else:
+            raise NotImplementedError("Contact the maintainer on [Discord](https://discord.com/invite/s3KuuzsPFb).")
         super().__init__(message)
 
 
diff --git a/lerobot/common/datasets/lerobot_dataset.py b/lerobot/common/datasets/lerobot_dataset.py
index 4fb71b3b..51eec779 100644
--- a/lerobot/common/datasets/lerobot_dataset.py
+++ b/lerobot/common/datasets/lerobot_dataset.py
@@ -17,15 +17,16 @@ import contextlib
 import logging
 import shutil
 from pathlib import Path
+import tempfile
 from typing import Callable
-
 import datasets
 import numpy as np
 import packaging.version
 import PIL.Image
+import pandas as pd
 import torch
 import torch.utils
-from datasets import concatenate_datasets, load_dataset
+from datasets import concatenate_datasets, load_dataset, Dataset
 from huggingface_hub import HfApi, snapshot_download
 from huggingface_hub.constants import REPOCARD_NAME
 from huggingface_hub.errors import RevisionNotFoundError
@@ -34,37 +35,57 @@ from lerobot.common.constants import HF_LEROBOT_HOME
 from lerobot.common.datasets.compute_stats import aggregate_stats, compute_episode_stats
 from lerobot.common.datasets.image_writer import AsyncImageWriter, write_image
 from lerobot.common.datasets.utils import (
+    DEFAULT_EPISODES_PATH,
+    DEFAULT_EPISODES_STATS_PATH,
     DEFAULT_FEATURES,
     DEFAULT_IMAGE_PATH,
+    EPISODES_DIR,
+    EPISODES_STATS_DIR,
     INFO_PATH,
-    TASKS_PATH,
+    LEGACY_TASKS_PATH,
     append_jsonlines,
     backward_compatible_episodes_stats,
     check_delta_timestamps,
     check_timestamps_sync,
     check_version_compatibility,
+    concat_video_files,
     create_empty_dataset_info,
     create_lerobot_dataset_card,
     embed_images,
+    get_chunk_file_indices,
     get_delta_indices,
     get_episode_data_index,
     get_features_from_robot,
+    get_hf_dataset_size_in_mb,
     get_hf_features_from_features,
+    get_latest_parquet_path,
+    get_latest_video_path,
+    get_parquet_num_frames,
+    get_pd_dataframe_size_in_mb,
     get_safe_version,
+    get_video_duration_in_s,
+    get_video_size_in_mb,
     hf_transform_to_torch,
     is_valid_version,
+    legacy_load_episodes,
+    legacy_load_episodes_stats,
     load_episodes,
     load_episodes_stats,
     load_info,
+    load_nested_dataset,
     load_stats,
+    legacy_load_tasks,
     load_tasks,
+    update_chunk_file_indices,
     validate_episode_buffer,
     validate_frame,
     write_episode,
-    write_episode_stats,
+    legacy_write_episode_stats,
     write_info,
     write_json,
+    write_tasks,
 )
+from lerobot.common.datasets.v30.convert_dataset_v21_to_v30 import get_parquet_file_size_in_mb
 from lerobot.common.datasets.video_utils import (
     VideoFrame,
     decode_video_frames_torchvision,
@@ -105,12 +126,9 @@ class LeRobotDatasetMetadata:
         check_version_compatibility(self.repo_id, self._version, CODEBASE_VERSION)
         self.tasks, self.task_to_task_index = load_tasks(self.root)
         self.episodes = load_episodes(self.root)
-        if self._version < packaging.version.parse("v2.1"):
-            self.stats = load_stats(self.root)
-            self.episodes_stats = backward_compatible_episodes_stats(self.stats, self.episodes)
-        else:
-            self.episodes_stats = load_episodes_stats(self.root)
-            self.stats = aggregate_stats(list(self.episodes_stats.values()))
+        self.episodes_stats = load_episodes_stats(self.root)
+        # TODO(rcadene): https://huggingface.slack.com/archives/C02V51Q3800/p1743517952388249?thread_ts=1742896075.499119&cid=C02V51Q3800
+        # self.stats = aggregate_stats(list(self.episodes_stats.values()))
 
     def pull_from_repo(
         self,
@@ -132,17 +150,19 @@ class LeRobotDatasetMetadata:
         return packaging.version.parse(self.info["codebase_version"])
 
     def get_data_file_path(self, ep_index: int) -> Path:
-        ep_chunk = self.get_episode_chunk(ep_index)
-        fpath = self.data_path.format(episode_chunk=ep_chunk, episode_index=ep_index)
+        chunk_idx = self.episodes[f"data/chunk_index"][ep_index]
+        file_idx = self.episodes[f"data/file_index"][ep_index]
+        fpath = self.data_path.format(chunk_index=chunk_idx, file_index=file_idx)
         return Path(fpath)
 
     def get_video_file_path(self, ep_index: int, vid_key: str) -> Path:
-        ep_chunk = self.get_episode_chunk(ep_index)
-        fpath = self.video_path.format(episode_chunk=ep_chunk, video_key=vid_key, episode_index=ep_index)
+        chunk_idx = self.episodes[f"{vid_key}/chunk_index"][ep_index]
+        file_idx = self.episodes[f"{vid_key}/file_index"][ep_index]
+        fpath = self.video_path.format(video_key=vid_key, chunk_index=chunk_idx, file_index=file_idx)
         return Path(fpath)
 
-    def get_episode_chunk(self, ep_index: int) -> int:
-        return ep_index // self.chunks_size
+    # def get_episode_chunk(self, ep_index: int) -> int:
+    #     return ep_index // self.chunks_size
 
     @property
     def data_path(self) -> str:
@@ -209,40 +229,85 @@ class LeRobotDatasetMetadata:
         """Total number of different tasks performed in this dataset."""
         return self.info["total_tasks"]
 
-    @property
-    def total_chunks(self) -> int:
-        """Total number of chunks (groups of episodes)."""
-        return self.info["total_chunks"]
-
     @property
     def chunks_size(self) -> int:
-        """Max number of episodes per chunk."""
+        """Max number of files per chunk."""
         return self.info["chunks_size"]
+    
+    @property
+    def files_size_in_mb(self) -> int:
+        """Max size of file in mega bytes."""
+        return self.info["files_size_in_mb"]
 
     def get_task_index(self, task: str) -> int | None:
         """
         Given a task in natural language, returns its task_index if the task already exists in the dataset,
         otherwise return None.
         """
-        return self.task_to_task_index.get(task, None)
+        return self.tasks.index[task] if task in self.tasks.index else None
+    
+    def has_task(self, task: str) -> bool:
+        return task in self.task_to_task_index
 
-    def add_task(self, task: str):
-        """
-        Given a task in natural language, add it to the dictionary of tasks.
-        """
-        if task in self.task_to_task_index:
-            raise ValueError(f"The task '{task}' already exists and can't be added twice.")
+    def save_episode_tasks(self, tasks: list[str]):
+        new_tasks = [task for task in tasks if not self.has_task(task)]
 
-        task_index = self.info["total_tasks"]
-        self.task_to_task_index[task] = task_index
-        self.tasks[task_index] = task
-        self.info["total_tasks"] += 1
+        for task in new_tasks:
+            task_index = len(self.tasks)
+            self.tasks.loc[task] = task_index
 
-        task_dict = {
-            "task_index": task_index,
-            "task": task,
-        }
-        append_jsonlines(task_dict, self.root / TASKS_PATH)
+        if len(new_tasks) > 0:
+            # Update on disk
+            write_tasks(self.tasks, self.root)
+
+    def _save_episode(self, episode_dict: dict):
+        ep_dataset = Dataset.from_dict(episode_dict)
+        ep_size_in_mb = get_hf_dataset_size_in_mb(ep_dataset)
+
+        # Access latest parquet file information
+        latest_path = get_latest_parquet_path(self.root / EPISODES_DIR)
+        latest_size_in_mb = get_parquet_file_size_in_mb(latest_path)
+        chunk_idx, file_idx = get_chunk_file_indices(latest_path)
+
+        if latest_size_in_mb + ep_size_in_mb >= self.meta.files_size_in_mb:
+            # Create new parquet file
+            chunk_idx, file_idx = update_chunk_file_indices(chunk_idx, file_idx, self.meta.chunks_size)
+            new_path = self.root / DEFAULT_EPISODES_PATH.format(chunk_index=chunk_idx, file_index=file_idx)
+            new_path.parent.mkdir(parents=True, exist_ok=True)
+            ep_df.to_parquet(new_path, index=False)
+        else:
+            # Update latest parquet file with new row
+            ep_df = pd.DataFrame(ep_dataset)
+            latest_df = pd.concat([latest_df, ep_df], ignore_index=True) # RAM
+            latest_df.to_parquet(latest_path, index=False)
+
+        # Update the Hugging Face dataset by reloading it.
+        # This process should be fast because only the latest Parquet file has been modified.
+        # Therefore, only this file needs to be converted to PyArrow; the rest is loaded from the PyArrow memory-mapped cache.
+        self.episodes = load_episodes(self.root)
+
+    def _save_episode_stats(self, episodes_stats: dict):
+        ep_dataset = Dataset.from_dict(episodes_stats)
+        ep_size_in_mb = get_hf_dataset_size_in_mb(ep_dataset)
+
+        # Access latest parquet file information
+        latest_path = get_latest_parquet_path(self.root / EPISODES_STATS_DIR)
+        latest_size_in_mb = get_parquet_file_size_in_mb(latest_path)
+        chunk_idx, file_idx = get_chunk_file_indices(latest_path)
+
+        if latest_size_in_mb + ep_size_in_mb >= self.meta.files_size_in_mb:
+            # Create new parquet file
+            chunk_idx, file_idx = update_chunk_file_indices(chunk_idx, file_idx, self.meta.chunks_size)
+            new_path = self.root / DEFAULT_EPISODES_STATS_PATH.format(chunk_index=chunk_idx, file_index=file_idx)
+            new_path.parent.mkdir(parents=True, exist_ok=True)
+            ep_df.to_parquet(new_path, index=False)
+        else:
+            # Update latest parquet file with new row
+            ep_df = pd.DataFrame(ep_dataset)
+            latest_df = pd.concat([latest_df, ep_df], ignore_index=True) # RAM
+            latest_df.to_parquet(latest_path, index=False)
+
+        self.episodes_stats = load_episodes_stats(self.root)
 
     def save_episode(
         self,
@@ -250,19 +315,14 @@ class LeRobotDatasetMetadata:
         episode_length: int,
         episode_tasks: list[str],
         episode_stats: dict[str, dict],
+        episode_metadata: dict,
     ) -> None:
+        # Update info
         self.info["total_episodes"] += 1
         self.info["total_frames"] += episode_length
-
-        chunk = self.get_episode_chunk(episode_index)
-        if chunk >= self.total_chunks:
-            self.info["total_chunks"] += 1
-
         self.info["splits"] = {"train": f"0:{self.info['total_episodes']}"}
-        self.info["total_videos"] += len(self.video_keys)
         if len(self.video_keys) > 0:
             self.update_video_info()
-
         write_info(self.info, self.root)
 
         episode_dict = {
@@ -270,12 +330,12 @@ class LeRobotDatasetMetadata:
             "tasks": episode_tasks,
             "length": episode_length,
         }
-        self.episodes[episode_index] = episode_dict
-        write_episode(episode_dict, self.root)
+        episode_dict.update(episode_metadata)
+        self._save_episode(episode_dict)
+        self._save_episode_stats(episode_stats)
 
-        self.episodes_stats[episode_index] = episode_stats
         self.stats = aggregate_stats([self.stats, episode_stats]) if self.stats else episode_stats
-        write_episode_stats(episode_index, episode_stats, self.root)
+        # TODO: write stats
 
     def update_video_info(self) -> None:
         """
@@ -340,8 +400,11 @@ class LeRobotDatasetMetadata:
 
             features = {**features, **DEFAULT_FEATURES}
 
-        obj.tasks, obj.task_to_task_index = {}, {}
-        obj.episodes_stats, obj.stats, obj.episodes = {}, {}, {}
+        obj.tasks = None
+        obj.episodes_stats = None
+        obj.episodes = None
+        # TODO(rcadene) stats
+        obj.stats = {}
         obj.info = create_empty_dataset_info(CODEBASE_VERSION, fps, robot_type, features, use_videos)
         if len(obj.video_keys) > 0 and not use_videos:
             raise ValueError()
@@ -486,29 +549,17 @@ class LeRobotDataset(torch.utils.data.Dataset):
         self.meta = LeRobotDatasetMetadata(
             self.repo_id, self.root, self.revision, force_cache_sync=force_cache_sync
         )
-        if self.episodes is not None and self.meta._version >= packaging.version.parse("v2.1"):
-            episodes_stats = [self.meta.episodes_stats[ep_idx] for ep_idx in self.episodes]
-            self.stats = aggregate_stats(episodes_stats)
 
         # Load actual data
         try:
             if force_cache_sync:
                 raise FileNotFoundError
-            assert all((self.root / fpath).is_file() for fpath in self.get_episodes_file_paths())
             self.hf_dataset = self.load_hf_dataset()
         except (AssertionError, FileNotFoundError, NotADirectoryError):
             self.revision = get_safe_version(self.repo_id, self.revision)
             self.download_episodes(download_videos)
             self.hf_dataset = self.load_hf_dataset()
 
-        self.episode_data_index = get_episode_data_index(self.meta.episodes, self.episodes)
-
-        # Check timestamps
-        timestamps = torch.stack(self.hf_dataset["timestamp"]).numpy()
-        episode_indices = torch.stack(self.hf_dataset["episode_index"]).numpy()
-        ep_data_index_np = {k: t.numpy() for k, t in self.episode_data_index.items()}
-        check_timestamps_sync(timestamps, episode_indices, ep_data_index_np, self.fps, self.tolerance_s)
-
         # Setup delta_indices
         if self.delta_timestamps is not None:
             check_delta_timestamps(self.delta_timestamps, self.fps, self.tolerance_s)
@@ -592,11 +643,10 @@ class LeRobotDataset(torch.utils.data.Dataset):
         """
         # TODO(rcadene, aliberts): implement faster transfer
         # https://huggingface.co/docs/huggingface_hub/en/guides/download#faster-downloads
-        files = None
         ignore_patterns = None if download_videos else "videos/"
+        files = None
         if self.episodes is not None:
             files = self.get_episodes_file_paths()
-
         self.pull_from_repo(allow_patterns=files, ignore_patterns=ignore_patterns)
 
     def get_episodes_file_paths(self) -> list[Path]:
@@ -609,31 +659,21 @@ class LeRobotDataset(torch.utils.data.Dataset):
                 for ep_idx in episodes
             ]
             fpaths += video_files
-
+        # episodes are stored in the same files, so we return unique paths only
+        fpaths = list(set(fpaths))
         return fpaths
 
     def load_hf_dataset(self) -> datasets.Dataset:
         """hf_dataset contains all the observations, states, actions, rewards, etc."""
-        if self.episodes is None:
-            path = str(self.root / "data")
-            # TODO(rcadene): load_dataset convert parquet to arrow.
-            # set num_proc to accelerate this conversion
-            hf_dataset = load_dataset("parquet", data_dir=path, split="train")
-        else:
-            files = [str(self.root / self.meta.get_data_file_path(ep_idx)) for ep_idx in self.episodes]
-            hf_dataset = load_dataset("parquet", data_files=files, split="train")
-
-        # TODO(aliberts): hf_dataset.set_format("torch")
-        hf_dataset.set_transform(hf_transform_to_torch)
+        hf_dataset = load_nested_dataset(self.root / "data")
+        hf_dataset.set_format("torch")
         return hf_dataset
 
     def create_hf_dataset(self) -> datasets.Dataset:
         features = get_hf_features_from_features(self.features)
         ft_dict = {col: [] for col in features}
         hf_dataset = datasets.Dataset.from_dict(ft_dict, features=features, split="train")
-
-        # TODO(aliberts): hf_dataset.set_format("torch")
-        hf_dataset.set_transform(hf_transform_to_torch)
+        hf_dataset.set_format("torch")
         return hf_dataset
 
     @property
@@ -664,15 +704,15 @@ class LeRobotDataset(torch.utils.data.Dataset):
             return get_hf_features_from_features(self.features)
 
     def _get_query_indices(self, idx: int, ep_idx: int) -> tuple[dict[str, list[int | bool]]]:
-        ep_start = self.episode_data_index["from"][ep_idx]
-        ep_end = self.episode_data_index["to"][ep_idx]
+        ep_start = self.meta.episodes["data/from_index"][ep_idx]
+        ep_end = self.meta.episodes["data/to_index"][ep_idx]
         query_indices = {
-            key: [max(ep_start.item(), min(ep_end.item() - 1, idx + delta)) for delta in delta_idx]
+            key: [max(ep_start, min(ep_end - 1, idx + delta)) for delta in delta_idx]
             for key, delta_idx in self.delta_indices.items()
         }
         padding = {  # Pad values outside of current episode range
             f"{key}_is_pad": torch.BoolTensor(
-                [(idx + delta < ep_start.item()) | (idx + delta >= ep_end.item()) for delta in delta_idx]
+                [(idx + delta < ep_start) | (idx + delta >= ep_end) for delta in delta_idx]
             )
             for key, delta_idx in self.delta_indices.items()
         }
@@ -687,7 +727,7 @@ class LeRobotDataset(torch.utils.data.Dataset):
         for key in self.meta.video_keys:
             if query_indices is not None and key in query_indices:
                 timestamps = self.hf_dataset.select(query_indices[key])["timestamp"]
-                query_timestamps[key] = torch.stack(timestamps).tolist()
+                query_timestamps[key] = timestamps.tolist()
             else:
                 query_timestamps[key] = [current_ts]
 
@@ -695,7 +735,7 @@ class LeRobotDataset(torch.utils.data.Dataset):
 
     def _query_hf_dataset(self, query_indices: dict[str, list[int]]) -> dict:
         return {
-            key: torch.stack(self.hf_dataset.select(q_idx)[key])
+            key: self.hf_dataset.select(q_idx)[key]
             for key, q_idx in query_indices.items()
             if key not in self.meta.video_keys
         }
@@ -708,9 +748,15 @@ class LeRobotDataset(torch.utils.data.Dataset):
         """
         item = {}
         for vid_key, query_ts in query_timestamps.items():
+            # Episodes are stored sequentially on a single mp4 to reduce the number of files.
+            # Thus we load the start timestamp of the episode on this mp4 and,
+            # shift the query timestamp accordingly.
+            from_timestamp = self.meta.episodes[f"{vid_key}/from_timestamp"][ep_idx]
+            shifted_query_ts = [from_timestamp + ts for ts in query_ts]
+
             video_path = self.root / self.meta.get_video_file_path(ep_idx, vid_key)
             frames = decode_video_frames_torchvision(
-                video_path, query_ts, self.tolerance_s, self.video_backend
+                video_path, shifted_query_ts, self.tolerance_s, self.video_backend
             )
             item[vid_key] = frames.squeeze(0)
 
@@ -749,7 +795,9 @@ class LeRobotDataset(torch.utils.data.Dataset):
 
         # Add task as a string
         task_idx = item["task_index"].item()
-        item["task"] = self.meta.tasks[task_idx]
+        if self.meta.tasks["task_index"][task_idx] != task_idx:
+            raise ValueError("Sanity check on task index failed.")
+        item["task"] = self.meta.tasks["task"][task_idx]
 
         return item
 
@@ -779,6 +827,9 @@ class LeRobotDataset(torch.utils.data.Dataset):
             image_key=image_key, episode_index=episode_index, frame_index=frame_index
         )
         return self.root / fpath
+    
+    def _get_image_file_dir(self, episode_index: int, image_key: str) -> Path:
+        return self._get_image_file_path(episode_index, image_key, frame_index=0).parent
 
     def _save_image(self, image: torch.Tensor | np.ndarray | PIL.Image.Image, fpath: Path) -> None:
         if self.image_writer is None:
@@ -858,11 +909,8 @@ class LeRobotDataset(torch.utils.data.Dataset):
         episode_buffer["index"] = np.arange(self.meta.total_frames, self.meta.total_frames + episode_length)
         episode_buffer["episode_index"] = np.full((episode_length,), episode_index)
 
-        # Add new tasks to the tasks dictionary
-        for task in episode_tasks:
-            task_index = self.meta.get_task_index(task)
-            if task_index is None:
-                self.meta.add_task(task)
+        # Update tasks and task indices with new tasks if any
+        self.meta.save_episode_tasks(episode_tasks)
 
         # Given tasks in natural language, find their corresponding task indices
         episode_buffer["task_index"] = np.array([self.meta.get_task_index(task) for task in tasks])
@@ -874,51 +922,107 @@ class LeRobotDataset(torch.utils.data.Dataset):
                 continue
             episode_buffer[key] = np.stack(episode_buffer[key])
 
+        # Wait for image writer to end, so that episode stats over images can be computed
         self._wait_image_writer()
-        self._save_episode_table(episode_buffer, episode_index)
         ep_stats = compute_episode_stats(episode_buffer, self.features)
 
-        if len(self.meta.video_keys) > 0:
-            video_paths = self.encode_episode_videos(episode_index)
-            for key in self.meta.video_keys:
-                episode_buffer[key] = video_paths[key]
+        ep_metadata = self._save_episode_data(episode_buffer, episode_index)
+        for video_key in self.meta.video_keys:
+            ep_metadata.update(self._save_episode_video(video_key, episode_index))
+        
+        # `meta.save_episode` neeed to be executed after encoding the videos
+        self.meta.save_episode(episode_index, episode_length, episode_tasks, ep_stats, ep_metadata)
 
-        # `meta.save_episode` be executed after encoding the videos
-        self.meta.save_episode(episode_index, episode_length, episode_tasks, ep_stats)
-
-        ep_data_index = get_episode_data_index(self.meta.episodes, [episode_index])
-        ep_data_index_np = {k: t.numpy() for k, t in ep_data_index.items()}
-        check_timestamps_sync(
-            episode_buffer["timestamp"],
-            episode_buffer["episode_index"],
-            ep_data_index_np,
-            self.fps,
-            self.tolerance_s,
-        )
-
-        video_files = list(self.root.rglob("*.mp4"))
-        assert len(video_files) == self.num_episodes * len(self.meta.video_keys)
-
-        parquet_files = list(self.root.rglob("*.parquet"))
-        assert len(parquet_files) == self.num_episodes
+        # TODO(rcadene): remove? there is only one episode in the episode buffer, no need for ep_data_index
+        # ep_data_index = get_episode_data_index(self.meta.episodes, [episode_index])
+        # ep_data_index_np = {k: t.numpy() for k, t in ep_data_index.items()}
+        # check_timestamps_sync(
+        #     episode_buffer["timestamp"],
+        #     episode_buffer["episode_index"],
+        #     ep_data_index_np,
+        #     self.fps,
+        #     self.tolerance_s,
+        # )
 
+        # TODO(rcadene): images are also deleted in clear_episode_buffer
         # delete images
         img_dir = self.root / "images"
         if img_dir.is_dir():
             shutil.rmtree(self.root / "images")
 
-        if not episode_data:  # Reset the buffer
+        if not episode_data:
+            # Reset episode buffer
             self.episode_buffer = self.create_episode_buffer()
 
-    def _save_episode_table(self, episode_buffer: dict, episode_index: int) -> None:
-        episode_dict = {key: episode_buffer[key] for key in self.hf_features}
-        ep_dataset = datasets.Dataset.from_dict(episode_dict, features=self.hf_features, split="train")
+    def _save_episode_data(self, episode_buffer: dict) -> None:
+        # Convert buffer into HF Dataset
+        ep_dict = {key: episode_buffer[key] for key in self.hf_features}
+        ep_dataset = datasets.Dataset.from_dict(ep_dict, features=self.hf_features, split="train")
         ep_dataset = embed_images(ep_dataset)
-        self.hf_dataset = concatenate_datasets([self.hf_dataset, ep_dataset])
-        self.hf_dataset.set_transform(hf_transform_to_torch)
-        ep_data_path = self.root / self.meta.get_data_file_path(ep_index=episode_index)
-        ep_data_path.parent.mkdir(parents=True, exist_ok=True)
-        ep_dataset.to_parquet(ep_data_path)
+        ep_size_in_mb = get_hf_dataset_size_in_mb(ep_dataset)
+        ep_num_frames = len(ep_dataset)
+
+        # Access latest parquet file information
+        latest_path = get_latest_parquet_path(self.root / "data")
+        latest_size_in_mb = get_parquet_file_size_in_mb(latest_path)
+        latest_num_frames = get_parquet_num_frames(latest_path)
+        chunk_idx, file_idx = get_chunk_file_indices(latest_path)
+
+        if latest_size_in_mb + ep_size_in_mb >= self.meta.files_size_in_mb:
+            # Create new parquet file
+            chunk_idx, file_idx = update_chunk_file_indices(chunk_idx, file_idx, self.meta.chunks_size)
+            new_path = self.meta.data_path.format(chunk_index=chunk_idx, file_index=file_idx)
+            new_path.parent.mkdir(parents=True, exist_ok=True)
+            ep_df.to_parquet(new_path, index=False)
+        else:
+            # Update latest parquet file with new rows
+            ep_df = pd.DataFrame(ep_dataset)
+            latest_df = pd.concat([latest_df, ep_df], ignore_index=True) # RAM
+            latest_df.to_parquet(latest_path, index=False)
+
+        # Update the Hugging Face dataset by reloading it.
+        # This process should be fast because only the latest Parquet file has been modified.
+        # Therefore, only this file needs to be converted to PyArrow; the rest is loaded from the PyArrow memory-mapped cache.
+        self.hf_dataset = self.load_hf_dataset()
+
+        metadata = {
+            "data/chunk_index": chunk_idx,
+            "data/file_index": file_idx,
+            "data/from_index": latest_num_frames,
+            "data/to_index": latest_num_frames + ep_num_frames,
+        }
+        return metadata
+
+    def _save_episode_video(self, video_key: str, episode_index: int):
+        # Encode episode frames into a temporary video
+        ep_path = self._encode_temporary_episode_video(video_key, episode_index)
+        ep_size_in_mb = get_video_size_in_mb(ep_path)
+        ep_duration_in_s = get_video_duration_in_s(ep_path)
+
+        # Access latest video file information
+        latest_path = get_latest_video_path(self.root / "videos", video_key)
+        latest_size_in_mb = get_video_size_in_mb(latest_path)
+        latest_duration_in_s = get_video_duration_in_s(latest_path)
+        chunk_idx, file_idx = get_chunk_file_indices(latest_path)
+
+        if latest_size_in_mb + ep_size_in_mb >= self.meta.files_size_in_mb:
+            # Move temporary episode video to a new video file in the dataset
+            chunk_idx, file_idx = update_chunk_file_indices(chunk_idx, file_idx, self.meta.chunks_size)
+            new_path = self.meta.video_path.format(video_key=video_key, chunk_index=chunk_idx, file_index=file_idx)
+            new_path.parent.mkdir(parents=True, exist_ok=True)
+            ep_path.replace(new_path)
+        else:
+            # Update latest video file
+            concat_video_files([latest_path, ep_path], self.root, video_key, chunk_idx, file_idx)
+
+        metadata = {
+            "episode_index": episode_index,
+            f"{video_key}/chunk_index": chunk_idx,
+            f"{video_key}/file_index": file_idx,
+            f"{video_key}/from_timestamp": latest_duration_in_s,
+            f"{video_key}/to_timestamp": latest_duration_in_s + ep_duration_in_s,
+        }
+        return metadata
 
     def clear_episode_buffer(self) -> None:
         episode_index = self.episode_buffer["episode_index"]
@@ -958,34 +1062,26 @@ class LeRobotDataset(torch.utils.data.Dataset):
         if self.image_writer is not None:
             self.image_writer.wait_until_done()
 
-    def encode_videos(self) -> None:
+    # TODO(rcadene): this method is currently not used
+    # def encode_videos(self) -> None:
+    #     """
+    #     Use ffmpeg to convert frames stored as png into mp4 videos.
+    #     Note: `encode_video_frames` is a blocking call. Making it asynchronous shouldn't speedup encoding,
+    #     since video encoding with ffmpeg is already using multithreading.
+    #     """
+    #     for ep_idx in range(self.meta.total_episodes):
+    #         self.encode_episode_videos(ep_idx)
+
+    def _encode_temporary_episode_video(self, video_key: str, episode_index: int) -> dict:
         """
         Use ffmpeg to convert frames stored as png into mp4 videos.
         Note: `encode_video_frames` is a blocking call. Making it asynchronous shouldn't speedup encoding,
         since video encoding with ffmpeg is already using multithreading.
         """
-        for ep_idx in range(self.meta.total_episodes):
-            self.encode_episode_videos(ep_idx)
-
-    def encode_episode_videos(self, episode_index: int) -> dict:
-        """
-        Use ffmpeg to convert frames stored as png into mp4 videos.
-        Note: `encode_video_frames` is a blocking call. Making it asynchronous shouldn't speedup encoding,
-        since video encoding with ffmpeg is already using multithreading.
-        """
-        video_paths = {}
-        for key in self.meta.video_keys:
-            video_path = self.root / self.meta.get_video_file_path(episode_index, key)
-            video_paths[key] = str(video_path)
-            if video_path.is_file():
-                # Skip if video is already encoded. Could be the case when resuming data recording.
-                continue
-            img_dir = self._get_image_file_path(
-                episode_index=episode_index, image_key=key, frame_index=0
-            ).parent
-            encode_video_frames(img_dir, video_path, self.fps, overwrite=True)
-
-        return video_paths
+        temp_path = Path(tempfile.mkdtemp()) / f"{video_key}_{episode_index:3d}.mp4"
+        img_dir = self._get_image_file_dir(episode_index, video_key)
+        encode_video_frames(img_dir, temp_path, self.fps, overwrite=True)
+        return temp_path
 
     @classmethod
     def create(
@@ -1030,7 +1126,6 @@ class LeRobotDataset(torch.utils.data.Dataset):
         obj.image_transforms = None
         obj.delta_timestamps = None
         obj.delta_indices = None
-        obj.episode_data_index = None
         obj.video_backend = video_backend if video_backend is not None else "pyav"
         return obj
 
diff --git a/lerobot/common/datasets/utils.py b/lerobot/common/datasets/utils.py
index 7e297b35..59a6d9a7 100644
--- a/lerobot/common/datasets/utils.py
+++ b/lerobot/common/datasets/utils.py
@@ -21,40 +21,62 @@ from collections.abc import Iterator
 from itertools import accumulate
 from pathlib import Path
 from pprint import pformat
+import subprocess
+import tempfile
 from types import SimpleNamespace
-from typing import Any
+from typing import Any, Tuple
 
 import datasets
 import jsonlines
 import numpy as np
 import packaging.version
+import pandas
 import torch
 from datasets.table import embed_table_storage
 from huggingface_hub import DatasetCard, DatasetCardData, HfApi
 from huggingface_hub.errors import RevisionNotFoundError
 from PIL import Image as PILImage
 from torchvision import transforms
+from datasets import Dataset, concatenate_datasets
 
 from lerobot.common.datasets.backward_compatibility import (
     V21_MESSAGE,
+    V30_MESSAGE,
     BackwardCompatibilityError,
     ForwardCompatibilityError,
 )
 from lerobot.common.robot_devices.robots.utils import Robot
 from lerobot.common.utils.utils import is_valid_numpy_dtype_string
 from lerobot.configs.types import DictLike, FeatureType, PolicyFeature
+import pyarrow.parquet as pq
 
-DEFAULT_CHUNK_SIZE = 1000  # Max number of episodes per chunk
+DEFAULT_CHUNK_SIZE = 1000  # Max number of files per chunk
+DEFAULT_FILE_SIZE_IN_MB = 500.0  # Max size per file
+
+# Keep legacy for `convert_dataset_v21_to_v30.py`
+LEGACY_EPISODES_PATH = "meta/episodes.jsonl"
+LEGACY_STATS_PATH = "meta/stats.json"
+LEGACY_EPISODES_STATS_PATH = "meta/episodes_stats.jsonl"
+LEGACY_TASKS_PATH = "meta/tasks.jsonl"
+LEGACY_DEFAULT_VIDEO_PATH = "videos/chunk-{episode_chunk:03d}/{video_key}/episode_{episode_index:06d}.mp4"
+LEGACY_DEFAULT_PARQUET_PATH = "data/chunk-{episode_chunk:03d}/episode_{episode_index:06d}.parquet"
+
+# TODO
+DEFAULT_IMAGE_PATH = "images/{image_key}/episode_{episode_index:06d}/frame_{frame_index:06d}.png"
+
+EPISODES_DIR = "meta/episodes"
+EPISODES_STATS_DIR = "meta/episodes_stats"
+TASKS_DIR = "meta/tasks"
+DATA_DIR = "data"
+VIDEO_DIR = "videos"
 
 INFO_PATH = "meta/info.json"
-EPISODES_PATH = "meta/episodes.jsonl"
-STATS_PATH = "meta/stats.json"
-EPISODES_STATS_PATH = "meta/episodes_stats.jsonl"
-TASKS_PATH = "meta/tasks.jsonl"
-
-DEFAULT_VIDEO_PATH = "videos/chunk-{episode_chunk:03d}/{video_key}/episode_{episode_index:06d}.mp4"
-DEFAULT_PARQUET_PATH = "data/chunk-{episode_chunk:03d}/episode_{episode_index:06d}.parquet"
-DEFAULT_IMAGE_PATH = "images/{image_key}/episode_{episode_index:06d}/frame_{frame_index:06d}.png"
+CHUNK_FILE_PATTERN = "chunk-{chunk_index:03d}/file-{file_index:03d}"
+DEFAULT_EPISODES_PATH = EPISODES_DIR + "/" + CHUNK_FILE_PATTERN + ".parquet"
+DEFAULT_EPISODES_STATS_PATH = EPISODES_STATS_DIR + "/" + CHUNK_FILE_PATTERN + ".parquet"
+DEFAULT_TASKS_PATH = TASKS_DIR + "/" + CHUNK_FILE_PATTERN + ".parquet"
+DEFAULT_DATA_PATH = DATA_DIR + "/" + CHUNK_FILE_PATTERN + ".parquet"
+DEFAULT_VIDEO_PATH = VIDEO_DIR + "/{video_key}/" + CHUNK_FILE_PATTERN + ".mp4"
 
 DATASET_CARD_TEMPLATE = """
 ---
@@ -75,6 +97,88 @@ DEFAULT_FEATURES = {
 }
 
 
+def get_hf_dataset_size_in_mb(hf_ds: Dataset) -> int:
+    return hf_ds.data.nbytes / (1024 ** 2)
+
+def get_pd_dataframe_size_in_mb(df: pandas.DataFrame) -> int:
+    memory_usage_bytes = df.memory_usage(deep=True).sum()
+    return memory_usage_bytes / (1024 ** 2)
+
+def get_chunk_file_indices(path: Path) -> Tuple[int, int]:
+    if not path.stem.startswith("file-") or not path.parent.name.startswith("chunk-"):
+        raise ValueError(f"Path does not follow {CHUNK_FILE_PATTERN}: '{path}'")
+
+    chunk_index = int(path.parent.replace("chunk-", ""))
+    file_index = int(path.stem.replace("file-", ""))
+    return chunk_index, file_index
+
+def update_chunk_file_indices(chunk_idx: int, file_idx: int, chunks_size: int):
+    if file_idx == chunks_size - 1:
+        file_idx = 0
+        chunk_idx += 1
+    else:
+        file_idx += 1
+    return chunk_idx, file_idx
+
+
+def load_nested_dataset(pq_dir: Path) -> Dataset:
+    """ Find parquet files in provided directory {pq_dir}/chunk-xxx/file-xxx.parquet
+        Convert parquet files to pyarrow memory mapped in a cache folder for efficient RAM usage
+        Concatenate all pyarrow references to return HF Dataset format
+    """
+    # TODO(rcadene): set num_proc to accelerate conversion to pyarrow
+    return concatenate_datasets([Dataset.from_parquet(str(path)) for path in sorted(pq_dir.glob("*/*.parquet"))])
+
+def get_latest_parquet_path(pq_dir: Path) -> Path:
+    return sorted(pq_dir.glob("*/*.parquet"))[-1]
+
+def get_latest_video_path(pq_dir: Path, video_key: str) -> Path:
+    return sorted(pq_dir.glob(f"{video_key}/*/*.mp4"))[-1]
+
+def get_parquet_num_frames(parquet_path):
+    metadata = pq.read_metadata(parquet_path)
+    return metadata.num_rows
+
+def get_video_size_in_mb(mp4_path: Path):
+    file_size_bytes = mp4_path.stat().st_size
+    file_size_mb = file_size_bytes / (1024 ** 2)
+    return file_size_mb
+
+def concat_video_files(paths_to_cat, new_root, video_key, chunk_idx, file_idx):
+    # Create a text file with the list of files to concatenate
+    with tempfile.NamedTemporaryFile(mode='w', delete=False, suffix='.txt') as f:
+        temp_file_path = f.name
+        for ep_path in paths_to_cat:
+            f.write(f"file '{str(ep_path)}'\n")
+
+    output_path = new_root / DEFAULT_VIDEO_PATH.format(video_key=video_key, chunk_index=chunk_idx, file_index=file_idx)
+    output_path.parent.mkdir(parents=True, exist_ok=True)
+    command = [
+        'ffmpeg',
+        '-y',
+        '-f', 'concat',
+        '-safe', '0',
+        '-i', str(temp_file_path),
+        '-c', 'copy',
+        str(output_path)
+    ]
+    subprocess.run(command, check=True)
+    Path(temp_file_path).unlink()
+
+def get_video_duration_in_s(mp4_file: Path):
+    result = subprocess.run(
+        [
+            'ffprobe',
+            '-v', 'error',
+            '-show_entries', 'format=duration',
+            '-of', 'default=noprint_wrappers=1:nokey=1',
+            mp4_file
+        ],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT
+    )
+    return float(result.stdout)
+
 def flatten_dict(d: dict, parent_key: str = "", sep: str = "/") -> dict:
     """Flatten a nested dictionary structure by collapsing nested keys into one key with a separator.
 
@@ -124,6 +228,8 @@ def serialize_dict(stats: dict[str, torch.Tensor | np.ndarray | dict]) -> dict:
     for key, value in flatten_dict(stats).items():
         if isinstance(value, (torch.Tensor, np.ndarray)):
             serialized_dict[key] = value.tolist()
+        elif isinstance(value, list) and isinstance(value[0], (int, float, list)):
+            serialized_dict[key] = value
         elif isinstance(value, np.generic):
             serialized_dict[key] = value.item()
         elif isinstance(value, (int, float)):
@@ -183,7 +289,7 @@ def load_info(local_dir: Path) -> dict:
 
 def write_stats(stats: dict, local_dir: Path):
     serialized_stats = serialize_dict(stats)
-    write_json(serialized_stats, local_dir / STATS_PATH)
+    write_json(serialized_stats, local_dir / LEGACY_STATS_PATH)
 
 
 def cast_stats_to_numpy(stats) -> dict[str, dict[str, np.ndarray]]:
@@ -192,50 +298,91 @@ def cast_stats_to_numpy(stats) -> dict[str, dict[str, np.ndarray]]:
 
 
 def load_stats(local_dir: Path) -> dict[str, dict[str, np.ndarray]]:
-    if not (local_dir / STATS_PATH).exists():
+    if not (local_dir / LEGACY_STATS_PATH).exists():
         return None
-    stats = load_json(local_dir / STATS_PATH)
+    stats = load_json(local_dir / LEGACY_STATS_PATH)
     return cast_stats_to_numpy(stats)
 
 
-def write_task(task_index: int, task: dict, local_dir: Path):
+def write_hf_dataset(hf_dataset: Dataset, local_dir: Path):
+    if get_hf_dataset_size_in_mb(hf_dataset) > DEFAULT_FILE_SIZE_IN_MB:
+        raise NotImplementedError("Contact a maintainer.")
+
+    path = local_dir / DEFAULT_DATA_PATH.format(chunk_index=0, file_index=0)
+    path.parent.mkdir(parents=True, exist_ok=True)
+    hf_dataset.to_parquet(path)
+
+
+def write_tasks(tasks: pandas.DataFrame, local_dir: Path):
+    path = local_dir / DEFAULT_TASKS_PATH.format(chunk_index=0, file_index=0)
+    path.parent.mkdir(parents=True, exist_ok=True)
+    tasks.to_parquet(path)
+
+def legacy_write_task(task_index: int, task: dict, local_dir: Path):
     task_dict = {
         "task_index": task_index,
         "task": task,
     }
-    append_jsonlines(task_dict, local_dir / TASKS_PATH)
+    append_jsonlines(task_dict, local_dir / LEGACY_TASKS_PATH)
 
 
-def load_tasks(local_dir: Path) -> tuple[dict, dict]:
-    tasks = load_jsonlines(local_dir / TASKS_PATH)
+def legacy_load_tasks(local_dir: Path) -> tuple[dict, dict]:
+    tasks = load_jsonlines(local_dir / LEGACY_TASKS_PATH)
     tasks = {item["task_index"]: item["task"] for item in sorted(tasks, key=lambda x: x["task_index"])}
     task_to_task_index = {task: task_index for task_index, task in tasks.items()}
     return tasks, task_to_task_index
 
+def load_tasks(local_dir: Path):
+    tasks = load_nested_dataset(local_dir / TASKS_DIR)
+    # TODO(rcadene): optimize this
+    task_to_task_index = {d["task"]: d["task_index"] for d in tasks}
+    return tasks, task_to_task_index
 
 def write_episode(episode: dict, local_dir: Path):
-    append_jsonlines(episode, local_dir / EPISODES_PATH)
+    append_jsonlines(episode, local_dir / LEGACY_EPISODES_PATH)
 
+def write_episodes(episodes: Dataset, local_dir: Path):
+    if get_hf_dataset_size_in_mb(episodes) > DEFAULT_FILE_SIZE_IN_MB:
+        raise NotImplementedError("Contact a maintainer.")
+    
+    fpath = local_dir / DEFAULT_EPISODES_PATH.format(chunk_index=0, file_index=0)
+    fpath.parent.mkdir(parents=True, exist_ok=True)
+    episodes.to_parquet(fpath)
 
-def load_episodes(local_dir: Path) -> dict:
-    episodes = load_jsonlines(local_dir / EPISODES_PATH)
+def legacy_load_episodes(local_dir: Path) -> dict:
+    episodes = load_jsonlines(local_dir / LEGACY_EPISODES_PATH)
     return {item["episode_index"]: item for item in sorted(episodes, key=lambda x: x["episode_index"])}
 
+def load_episodes(local_dir: Path):
+    hf_dataset = load_nested_dataset(local_dir / EPISODES_DIR)
+    return hf_dataset
 
-def write_episode_stats(episode_index: int, episode_stats: dict, local_dir: Path):
+def legacy_write_episode_stats(episode_index: int, episode_stats: dict, local_dir: Path):
     # We wrap episode_stats in a dictionary since `episode_stats["episode_index"]`
     # is a dictionary of stats and not an integer.
     episode_stats = {"episode_index": episode_index, "stats": serialize_dict(episode_stats)}
-    append_jsonlines(episode_stats, local_dir / EPISODES_STATS_PATH)
+    append_jsonlines(episode_stats, local_dir / LEGACY_EPISODES_STATS_PATH)
 
 
-def load_episodes_stats(local_dir: Path) -> dict:
-    episodes_stats = load_jsonlines(local_dir / EPISODES_STATS_PATH)
+def write_episodes_stats(episodes_stats: Dataset, local_dir: Path):
+    if get_hf_dataset_size_in_mb(episodes_stats) > DEFAULT_FILE_SIZE_IN_MB:
+        raise NotImplementedError("Contact a maintainer.")
+    
+    fpath = local_dir / DEFAULT_EPISODES_STATS_PATH.format(chunk_index=0, file_index=0)
+    fpath.parent.mkdir(parents=True, exist_ok=True)
+    episodes_stats.to_parquet(fpath)
+
+
+def legacy_load_episodes_stats(local_dir: Path) -> dict:
+    episodes_stats = load_jsonlines(local_dir / LEGACY_EPISODES_STATS_PATH)
     return {
         item["episode_index"]: cast_stats_to_numpy(item["stats"])
         for item in sorted(episodes_stats, key=lambda x: x["episode_index"])
     }
 
+def load_episodes_stats(local_dir: Path):
+    hf_dataset = load_nested_dataset(local_dir / EPISODES_STATS_DIR)
+    return hf_dataset
 
 def backward_compatible_episodes_stats(
     stats: dict[str, dict[str, np.ndarray]], episodes: list[int]
@@ -388,6 +535,7 @@ def get_hf_features_from_features(features: dict) -> datasets.Features:
 
 
 def get_features_from_robot(robot: Robot, use_videos: bool = True) -> dict:
+    # TODO(rcadene): add fps for each feature
     camera_ft = {}
     if robot.cameras:
         camera_ft = {
@@ -442,11 +590,11 @@ def create_empty_dataset_info(
         "total_frames": 0,
         "total_tasks": 0,
         "total_videos": 0,
-        "total_chunks": 0,
         "chunks_size": DEFAULT_CHUNK_SIZE,
+        "files_size_in_mb": DEFAULT_FILE_SIZE_IN_MB,
         "fps": fps,
         "splits": {},
-        "data_path": DEFAULT_PARQUET_PATH,
+        "data_path": DEFAULT_DATA_PATH,
         "video_path": DEFAULT_VIDEO_PATH if use_videos else None,
         "features": features,
     }
diff --git a/lerobot/common/datasets/v2/convert_dataset_v1_to_v2.py b/lerobot/common/datasets/v2/convert_dataset_v1_to_v2.py
index acf0282f..38f852bb 100644
--- a/lerobot/common/datasets/v2/convert_dataset_v1_to_v2.py
+++ b/lerobot/common/datasets/v2/convert_dataset_v1_to_v2.py
@@ -121,12 +121,12 @@ from safetensors.torch import load_file
 
 from lerobot.common.datasets.utils import (
     DEFAULT_CHUNK_SIZE,
-    DEFAULT_PARQUET_PATH,
+    DEFAULT_DATA_PATH,
     DEFAULT_VIDEO_PATH,
-    EPISODES_PATH,
+    LEGACY_EPISODES_PATH,
     INFO_PATH,
-    STATS_PATH,
-    TASKS_PATH,
+    LEGACY_STATS_PATH,
+    LEGACY_TASKS_PATH,
     create_branch,
     create_lerobot_dataset_card,
     flatten_dict,
@@ -188,7 +188,7 @@ def convert_stats_to_json(v1_dir: Path, v2_dir: Path) -> None:
     serialized_stats = {key: value.tolist() for key, value in stats.items()}
     serialized_stats = unflatten_dict(serialized_stats)
 
-    json_path = v2_dir / STATS_PATH
+    json_path = v2_dir / LEGACY_STATS_PATH
     json_path.parent.mkdir(exist_ok=True, parents=True)
     with open(json_path, "w") as f:
         json.dump(serialized_stats, f, indent=4)
@@ -291,12 +291,12 @@ def split_parquet_by_episodes(
     for ep_chunk in range(total_chunks):
         ep_chunk_start = DEFAULT_CHUNK_SIZE * ep_chunk
         ep_chunk_end = min(DEFAULT_CHUNK_SIZE * (ep_chunk + 1), total_episodes)
-        chunk_dir = "/".join(DEFAULT_PARQUET_PATH.split("/")[:-1]).format(episode_chunk=ep_chunk)
+        chunk_dir = "/".join(DEFAULT_DATA_PATH.split("/")[:-1]).format(episode_chunk=ep_chunk)
         (output_dir / chunk_dir).mkdir(parents=True, exist_ok=True)
         for ep_idx in range(ep_chunk_start, ep_chunk_end):
             ep_table = table.filter(pc.equal(table["episode_index"], ep_idx))
             episode_lengths.insert(ep_idx, len(ep_table))
-            output_file = output_dir / DEFAULT_PARQUET_PATH.format(
+            output_file = output_dir / DEFAULT_DATA_PATH.format(
                 episode_chunk=ep_chunk, episode_index=ep_idx
             )
             pq.write_table(ep_table, output_file)
@@ -496,7 +496,7 @@ def convert_dataset(
 
     assert set(tasks) == {task for ep_tasks in tasks_by_episodes.values() for task in ep_tasks}
     tasks = [{"task_index": task_idx, "task": task} for task_idx, task in enumerate(tasks)]
-    write_jsonlines(tasks, v20_dir / TASKS_PATH)
+    write_jsonlines(tasks, v20_dir / LEGACY_TASKS_PATH)
     features["task_index"] = {
         "dtype": "int64",
         "shape": (1,),
@@ -546,7 +546,7 @@ def convert_dataset(
         {"episode_index": ep_idx, "tasks": tasks_by_episodes[ep_idx], "length": episode_lengths[ep_idx]}
         for ep_idx in episode_indices
     ]
-    write_jsonlines(episodes, v20_dir / EPISODES_PATH)
+    write_jsonlines(episodes, v20_dir / LEGACY_EPISODES_PATH)
 
     # Assemble metadata v2.0
     metadata_v2_0 = {
@@ -560,7 +560,7 @@ def convert_dataset(
         "chunks_size": DEFAULT_CHUNK_SIZE,
         "fps": metadata_v1["fps"],
         "splits": {"train": f"0:{total_episodes}"},
-        "data_path": DEFAULT_PARQUET_PATH,
+        "data_path": DEFAULT_DATA_PATH,
         "video_path": DEFAULT_VIDEO_PATH if video_keys else None,
         "features": features,
     }
diff --git a/lerobot/common/datasets/v21/convert_dataset_v20_to_v21.py b/lerobot/common/datasets/v21/convert_dataset_v20_to_v21.py
index 163a6003..8d291b64 100644
--- a/lerobot/common/datasets/v21/convert_dataset_v20_to_v21.py
+++ b/lerobot/common/datasets/v21/convert_dataset_v20_to_v21.py
@@ -23,7 +23,7 @@ import logging
 from huggingface_hub import HfApi
 
 from lerobot.common.datasets.lerobot_dataset import CODEBASE_VERSION, LeRobotDataset
-from lerobot.common.datasets.utils import EPISODES_STATS_PATH, STATS_PATH, load_stats, write_info
+from lerobot.common.datasets.utils import LEGACY_EPISODES_STATS_PATH, LEGACY_STATS_PATH, load_stats, write_info
 from lerobot.common.datasets.v21.convert_stats import check_aggregate_stats, convert_stats
 
 V20 = "v2.0"
@@ -47,8 +47,8 @@ def convert_dataset(
     with SuppressWarnings():
         dataset = LeRobotDataset(repo_id, revision=V20, force_cache_sync=True)
 
-    if (dataset.root / EPISODES_STATS_PATH).is_file():
-        (dataset.root / EPISODES_STATS_PATH).unlink()
+    if (dataset.root / LEGACY_EPISODES_STATS_PATH).is_file():
+        (dataset.root / LEGACY_EPISODES_STATS_PATH).unlink()
 
     convert_stats(dataset, num_workers=num_workers)
     ref_stats = load_stats(dataset.root)
@@ -60,15 +60,15 @@ def convert_dataset(
     dataset.push_to_hub(branch=branch, tag_version=False, allow_patterns="meta/")
 
     # delete old stats.json file
-    if (dataset.root / STATS_PATH).is_file:
-        (dataset.root / STATS_PATH).unlink()
+    if (dataset.root / LEGACY_STATS_PATH).is_file:
+        (dataset.root / LEGACY_STATS_PATH).unlink()
 
     hub_api = HfApi()
     if hub_api.file_exists(
-        repo_id=dataset.repo_id, filename=STATS_PATH, revision=branch, repo_type="dataset"
+        repo_id=dataset.repo_id, filename=LEGACY_STATS_PATH, revision=branch, repo_type="dataset"
     ):
         hub_api.delete_file(
-            path_in_repo=STATS_PATH, repo_id=dataset.repo_id, revision=branch, repo_type="dataset"
+            path_in_repo=LEGACY_STATS_PATH, repo_id=dataset.repo_id, revision=branch, repo_type="dataset"
         )
 
     hub_api.create_tag(repo_id, tag=CODEBASE_VERSION, revision=branch, repo_type="dataset")
diff --git a/lerobot/common/datasets/v21/convert_stats.py b/lerobot/common/datasets/v21/convert_stats.py
index cbf584b7..cd0f23fe 100644
--- a/lerobot/common/datasets/v21/convert_stats.py
+++ b/lerobot/common/datasets/v21/convert_stats.py
@@ -5,7 +5,7 @@ from tqdm import tqdm
 
 from lerobot.common.datasets.compute_stats import aggregate_stats, get_feature_stats, sample_indices
 from lerobot.common.datasets.lerobot_dataset import LeRobotDataset
-from lerobot.common.datasets.utils import write_episode_stats
+from lerobot.common.datasets.utils import legacy_write_episode_stats
 
 
 def sample_episode_video_frames(dataset: LeRobotDataset, episode_index: int, ft_key: str) -> np.ndarray:
@@ -58,7 +58,7 @@ def convert_stats(dataset: LeRobotDataset, num_workers: int = 0):
             convert_episode_stats(dataset, ep_idx)
 
     for ep_idx in tqdm(range(total_episodes)):
-        write_episode_stats(ep_idx, dataset.meta.episodes_stats[ep_idx], dataset.root)
+        legacy_write_episode_stats(ep_idx, dataset.meta.episodes_stats[ep_idx], dataset.root)
 
 
 def check_aggregate_stats(
diff --git a/lerobot/common/datasets/v30/convert_dataset_v21_to_v30.py b/lerobot/common/datasets/v30/convert_dataset_v21_to_v30.py
index f1efae35..d066af88 100644
--- a/lerobot/common/datasets/v30/convert_dataset_v21_to_v30.py
+++ b/lerobot/common/datasets/v30/convert_dataset_v21_to_v30.py
@@ -19,26 +19,301 @@ python lerobot/common/datasets/v30/convert_dataset_v21_to_v30.py \
 
 import argparse
 import logging
+from pathlib import Path
+import sys
 
 from datasets import Dataset
 from huggingface_hub import snapshot_download
+import tqdm
 
 from lerobot.common.constants import HF_LEROBOT_HOME
 from lerobot.common.datasets.utils import (
-    load_episodes_stats,
+    DEFAULT_CHUNK_SIZE,
+    DEFAULT_DATA_PATH,
+    DEFAULT_FILE_SIZE_IN_MB,
+    DEFAULT_VIDEO_PATH,
+    concat_video_files,
+    flatten_dict,
+    get_parquet_num_frames,
+    get_video_duration_in_s,
+    get_video_size_in_mb,
+    legacy_load_episodes,
+    legacy_load_episodes_stats,
+    load_info,
+    legacy_load_tasks,
+    update_chunk_file_indices,
+    write_episodes,
+    write_episodes_stats,
+    write_info,
+    write_tasks,
 )
+import subprocess
+import tempfile
+import pandas as pd
+import pyarrow.parquet as pq
 
 V21 = "v2.1"
 
 
-class SuppressWarnings:
-    def __enter__(self):
-        self.previous_level = logging.getLogger().getEffectiveLevel()
-        logging.getLogger().setLevel(logging.ERROR)
+"""
+-------------------------
+OLD
+data/chunk-000/episode_000000.parquet
 
-    def __exit__(self, exc_type, exc_val, exc_tb):
-        logging.getLogger().setLevel(self.previous_level)
+NEW
+data/chunk-000/file_000.parquet
+-------------------------
+OLD
+videos/chunk-000/CAMERA/episode_000000.mp4
 
+NEW
+videos/chunk-000/file_000.mp4
+-------------------------
+OLD
+episodes.jsonl
+{"episode_index": 1, "tasks": ["Put the blue block in the green bowl"], "length": 266}
+
+NEW
+meta/episodes/chunk-000/episodes_000.parquet
+episode_index | video_chunk_index | video_file_index | data_chunk_index | data_file_index | tasks | length
+-------------------------
+OLD
+tasks.jsonl
+{"task_index": 1, "task": "Put the blue block in the green bowl"}
+
+NEW
+meta/tasks/chunk-000/file_000.parquet
+task_index | task
+-------------------------
+OLD
+episodes_stats.jsonl
+
+NEW
+meta/episodes_stats/chunk-000/file_000.parquet
+episode_index | mean | std | min | max
+-------------------------
+UPDATE
+meta/info.json
+-------------------------
+"""
+
+def get_parquet_file_size_in_mb(parquet_path):
+    metadata = pq.read_metadata(parquet_path)
+    uncompressed_size = metadata.num_rows * metadata.row_group(0).total_byte_size
+    return uncompressed_size / (1024 ** 2)
+
+
+
+def generate_flat_ep_stats(episodes_stats):
+    for ep_idx, ep_stats in episodes_stats.items():
+        flat_ep_stats = flatten_dict(ep_stats)
+        flat_ep_stats["episode_index"] = ep_idx
+        yield flat_ep_stats
+
+def convert_episodes_stats(root, new_root):
+    episodes_stats = legacy_load_episodes_stats(root)
+    ds_episodes_stats = Dataset.from_generator(lambda: generate_flat_ep_stats(episodes_stats))
+    write_episodes_stats(ds_episodes_stats, new_root)
+
+def generate_task_dict(tasks):
+    for task_index, task in tasks.items():
+        yield {"task_index": task_index, "task": task}
+
+def convert_tasks(root, new_root):
+    tasks, _ = legacy_load_tasks(root)
+    ds_tasks = Dataset.from_generator(lambda: generate_task_dict(tasks))
+    write_tasks(ds_tasks, new_root)
+
+
+def concat_data_files(paths_to_cat, new_root, chunk_idx, file_idx):
+    # TODO(rcadene): to save RAM use Dataset.from_parquet(file) and concatenate_datasets
+    dataframes = [pd.read_parquet(file) for file in paths_to_cat]
+    # Concatenate all DataFrames along rows
+    concatenated_df = pd.concat(dataframes, ignore_index=True)
+
+    path = new_root / DEFAULT_DATA_PATH.format(chunk_index=chunk_idx, file_index=file_idx)
+    path.parent.mkdir(parents=True, exist_ok=True)
+    concatenated_df.to_parquet(path, index=False)
+
+
+def convert_data(root, new_root):
+    data_dir = root / "data"
+
+    ep_paths = [path for path in data_dir.glob("*/*.parquet")]
+    ep_paths = sorted(ep_paths)
+
+    episodes_metadata = []
+    ep_idx = 0
+    chunk_idx = 0
+    file_idx = 0
+    size_in_mb = 0
+    num_frames = 0
+    paths_to_cat = []
+    for ep_path in ep_paths:
+        ep_size_in_mb = get_parquet_file_size_in_mb(ep_path)
+        ep_num_frames = get_parquet_num_frames(ep_path)
+        ep_metadata = {
+            "episode_index": ep_idx,
+            "data/chunk_index": chunk_idx,
+            "data/file_index": file_idx,
+            "data/from_index": num_frames,
+            "data/to_index": num_frames + ep_num_frames,
+        }
+        size_in_mb += ep_size_in_mb
+        num_frames += ep_num_frames
+        episodes_metadata.append(ep_metadata)
+        ep_idx += 1
+
+        if size_in_mb < DEFAULT_FILE_SIZE_IN_MB:
+            paths_to_cat.append(ep_path)
+            continue
+
+        concat_data_files(paths_to_cat, new_root, chunk_idx, file_idx)
+
+        # Reset for the next file
+        size_in_mb = ep_size_in_mb
+        num_frames = ep_num_frames
+        paths_to_cat = [ep_path]
+
+        chunk_idx, file_idx = update_chunk_file_indices(chunk_idx, file_idx, DEFAULT_CHUNK_SIZE)
+
+    # Write remaining data if any
+    if paths_to_cat:
+        concat_data_files(paths_to_cat, new_root, chunk_idx, file_idx)
+
+    return episodes_metadata
+
+
+
+def get_video_keys(root):
+    info = load_info(root)
+    features = info["features"]
+    image_keys = [key for key, ft in features.items() if ft["dtype"] == "image"]
+    if len(image_keys) != 0:
+        raise NotImplementedError()
+
+    video_keys = [key for key, ft in features.items() if ft["dtype"] == "video"]
+    return video_keys
+
+
+def convert_videos(root: Path, new_root: Path):
+    video_keys = get_video_keys(root)
+    video_keys = sorted(video_keys)
+
+    eps_metadata_per_cam = []
+    for camera in video_keys:
+        eps_metadata = convert_videos_of_camera(root, new_root, camera)
+        eps_metadata_per_cam.append(eps_metadata)
+    
+    num_eps_per_cam = [len(eps_cam_map) for eps_cam_map in eps_metadata_per_cam]
+    if len(set(num_eps_per_cam)) != 1:
+        raise ValueError(f"All cams dont have same number of episodes ({num_eps_per_cam}).")
+    
+    episods_metadata = []
+    num_cameras = len(video_keys)
+    num_episodes = num_eps_per_cam[0]
+    for ep_idx in range(num_episodes):
+        # Sanity check
+        ep_ids = [eps_metadata_per_cam[cam_idx][ep_idx]["episode_index"] for cam_idx in range(num_cameras)]
+        ep_ids += [ep_idx]
+        if len(set(ep_ids)) != 1:
+            raise ValueError(f"All episode indices need to match ({ep_ids}).")
+
+        ep_dict = {}
+        for cam_idx in range(num_cameras):
+            ep_dict.update(eps_metadata_per_cam[cam_idx][ep_idx])
+        episods_metadata.append(ep_dict)
+            
+    return episods_metadata
+
+
+def convert_videos_of_camera(root: Path, new_root: Path, video_key):
+    # Access old paths to mp4
+    videos_dir = root / "videos"
+    ep_paths = [path for path in videos_dir.glob(f"*/{video_key}/*.mp4")]
+    ep_paths = sorted(ep_paths)
+
+    episodes_metadata = []
+    ep_idx = 0
+    chunk_idx = 0
+    file_idx = 0
+    size_in_mb = 0
+    duration_in_s = 0.0
+    paths_to_cat = []
+    for ep_path in tqdm.tqdm(ep_paths, desc=f"convert videos of {video_key}"):
+        ep_size_in_mb = get_video_size_in_mb(ep_path)
+        ep_duration_in_s = get_video_duration_in_s(ep_path)
+        ep_metadata = {
+            "episode_index": ep_idx,
+            f"{video_key}/chunk_index": chunk_idx,
+            f"{video_key}/file_index": file_idx,
+            f"{video_key}/from_timestamp": duration_in_s,
+            f"{video_key}/to_timestamp": duration_in_s + ep_duration_in_s,
+        }
+        size_in_mb += ep_size_in_mb
+        duration_in_s += ep_duration_in_s
+        episodes_metadata.append(ep_metadata)
+        ep_idx += 1
+
+        if size_in_mb < DEFAULT_FILE_SIZE_IN_MB:
+            paths_to_cat.append(ep_path)
+            continue
+
+        concat_video_files(paths_to_cat, new_root, video_key, chunk_idx, file_idx)
+
+        # Reset for the next file
+        size_in_mb = ep_size_in_mb
+        duration_in_s = ep_duration_in_s
+        paths_to_cat = [ep_path]
+
+        chunk_idx, file_idx = update_chunk_file_indices(chunk_idx, file_idx, DEFAULT_CHUNK_SIZE)
+
+    # Write remaining videos if any
+    if paths_to_cat:
+        concat_video_files(paths_to_cat, new_root, video_key, chunk_idx, file_idx)
+
+    return episodes_metadata
+
+def generate_episode_dict(episodes, episodes_data, episodes_videos):
+    for ep, ep_data, ep_video in zip(episodes.values(), episodes_data, episodes_videos):
+        ep_idx = ep["episode_index"]
+        ep_idx_data = ep_data["episode_index"]
+        ep_idx_video = ep_video["episode_index"]
+
+        if len(set([ep_idx, ep_idx_data, ep_idx_video])) != 1:
+            raise ValueError(f"Number of episodes is not the same ({ep_idx=},{ep_idx_data=},{ep_idx_video=}).")
+
+        ep_dict = {**ep_data, **ep_video, **ep}
+        yield ep_dict
+
+def convert_episodes(root, new_root, episodes_data, episodes_videos):
+    episodes = legacy_load_episodes(root)
+
+    num_eps = len(episodes)
+    num_eps_data = len(episodes_data)
+    num_eps_video = len(episodes_videos)
+    if len(set([num_eps, num_eps_data, num_eps_video])) != 1:
+        raise ValueError(f"Number of episodes is not the same ({num_eps=},{num_eps_data=},{num_eps_video=}).")
+
+    ds_episodes = Dataset.from_generator(lambda: generate_episode_dict(episodes, episodes_data, episodes_videos))
+    write_episodes(ds_episodes, new_root)
+
+def convert_info(root, new_root):
+    info = load_info(root)
+    info["codebase_version"] = "v3.0"
+    del info["total_chunks"]
+    del info["total_videos"]
+    info["files_size_in_mb"] = DEFAULT_FILE_SIZE_IN_MB
+    # TODO(rcadene): chunk- or chunk_ or file- or file_
+    info["data_path"] = DEFAULT_DATA_PATH
+    info["video_path"] = DEFAULT_VIDEO_PATH
+    info["fps"] = float(info["fps"])
+    for key in info["features"]:
+        if info["features"][key]["dtype"] == "video":
+            # already has fps in video_info
+            continue
+        info["features"][key]["fps"] = info["fps"]
+    write_info(info, new_root)
 
 def convert_dataset(
     repo_id: str,
@@ -46,6 +321,8 @@ def convert_dataset(
     num_workers: int = 4,
 ):
     root = HF_LEROBOT_HOME / repo_id
+    new_root = HF_LEROBOT_HOME / f"{repo_id}_v30"
+
     snapshot_download(
         repo_id,
         repo_type="dataset",
@@ -53,63 +330,12 @@ def convert_dataset(
         local_dir=root,
     )
 
-    # Concatenate videos
-
-    # Create
-
-    """
-    -------------------------
-    OLD
-    data/chunk-000/episode_000000.parquet
-
-    NEW
-    data/chunk-000/file_000.parquet
-    -------------------------
-    OLD
-    videos/chunk-000/CAMERA/episode_000000.mp4
-
-    NEW
-    videos/chunk-000/file_000.mp4
-    -------------------------
-    OLD
-    episodes.jsonl
-    {"episode_index": 1, "tasks": ["Put the blue block in the green bowl"], "length": 266}
-
-    NEW
-    meta/episodes/chunk-000/episodes_000.parquet
-    episode_index | video_chunk_index | video_file_index | data_chunk_index | data_file_index | tasks | length
-    -------------------------
-    OLD
-    tasks.jsonl
-    {"task_index": 1, "task": "Put the blue block in the green bowl"}
-
-    NEW
-    meta/tasks/chunk-000/file_000.parquet
-    task_index | task
-    -------------------------
-    OLD
-    episodes_stats.jsonl
-
-    NEW
-    meta/episodes_stats/chunk-000/file_000.parquet
-    episode_index | mean | std | min | max
-    -------------------------
-    UPDATE
-    meta/info.json
-    -------------------------
-    """
-
-    new_root = HF_LEROBOT_HOME / f"{repo_id}_v30"
-    new_root.mkdir(parents=True, exist_ok=True)
-
-    episodes_stats = load_episodes_stats(root)
-    hf_dataset = Dataset.from_dict(episodes_stats)  # noqa: F841
-
-    meta_ep_st_ch = new_root / "meta/episodes_stats/chunk-000"
-    meta_ep_st_ch.mkdir(parents=True, exist_ok=True)
-
-    # hf_dataset.to_parquet(meta_ep_st_ch / 'file_000.parquet')
-
+    convert_info(root, new_root)
+    convert_episodes_stats(root, new_root)
+    convert_tasks(root, new_root)    
+    episodes_data_mapping = convert_data(root, new_root)
+    episodes_videos_mapping = convert_videos(root, new_root)
+    convert_episodes(root, new_root, episodes_data_mapping, episodes_videos_mapping)
 
 if __name__ == "__main__":
     parser = argparse.ArgumentParser()
diff --git a/tests/fixtures/dataset_factories.py b/tests/fixtures/dataset_factories.py
index 2259e0e6..beed2eb7 100644
--- a/tests/fixtures/dataset_factories.py
+++ b/tests/fixtures/dataset_factories.py
@@ -9,13 +9,16 @@ import numpy as np
 import PIL.Image
 import pytest
 import torch
+from datasets import Dataset
 
 from lerobot.common.datasets.lerobot_dataset import CODEBASE_VERSION, LeRobotDataset, LeRobotDatasetMetadata
 from lerobot.common.datasets.utils import (
     DEFAULT_CHUNK_SIZE,
     DEFAULT_FEATURES,
-    DEFAULT_PARQUET_PATH,
+    DEFAULT_DATA_PATH,
+    DEFAULT_FILE_SIZE_IN_MB,
     DEFAULT_VIDEO_PATH,
+    flatten_dict,
     get_hf_features_from_features,
     hf_transform_to_torch,
 )
@@ -33,10 +36,9 @@ class LeRobotDatasetFactory(Protocol):
     def __call__(self, *args, **kwargs) -> LeRobotDataset: ...
 
 
-def get_task_index(task_dicts: dict, task: str) -> int:
-    tasks = {d["task_index"]: d["task"] for d in task_dicts.values()}
-    task_to_task_index = {task: task_idx for task_idx, task in tasks.items()}
-    return task_to_task_index[task]
+def get_task_index(tasks: Dataset, task: str) -> int:
+    task_idx = tasks["task"].index(task)
+    return task_idx
 
 
 @pytest.fixture(scope="session")
@@ -104,9 +106,9 @@ def info_factory(features_factory):
         total_frames: int = 0,
         total_tasks: int = 0,
         total_videos: int = 0,
-        total_chunks: int = 0,
         chunks_size: int = DEFAULT_CHUNK_SIZE,
-        data_path: str = DEFAULT_PARQUET_PATH,
+        files_size_in_mb: float = DEFAULT_FILE_SIZE_IN_MB,
+        data_path: str = DEFAULT_DATA_PATH,
         video_path: str = DEFAULT_VIDEO_PATH,
         motor_features: dict = DUMMY_MOTOR_FEATURES,
         camera_features: dict = DUMMY_CAMERA_FEATURES,
@@ -120,8 +122,8 @@ def info_factory(features_factory):
             "total_frames": total_frames,
             "total_tasks": total_tasks,
             "total_videos": total_videos,
-            "total_chunks": total_chunks,
             "chunks_size": chunks_size,
+            "files_size_in_mb": files_size_in_mb,
             "fps": fps,
             "splits": {},
             "data_path": data_path,
@@ -168,25 +170,25 @@ def episodes_stats_factory(stats_factory):
         features: dict[str],
         total_episodes: int = 3,
     ) -> dict:
-        episodes_stats = {}
-        for episode_index in range(total_episodes):
-            episodes_stats[episode_index] = {
-                "episode_index": episode_index,
-                "stats": stats_factory(features),
-            }
-        return episodes_stats
+        
+        def _generator(total_episodes):
+            for ep_idx in range(total_episodes):
+                flat_ep_stats = flatten_dict(stats_factory(features))
+                flat_ep_stats["episode_index"] = ep_idx
+                yield flat_ep_stats
+
+        # Simpler to rely on generator instead of from_dict
+        return Dataset.from_generator(lambda: _generator(total_episodes))
 
     return _create_episodes_stats
 
 
 @pytest.fixture(scope="session")
 def tasks_factory():
-    def _create_tasks(total_tasks: int = 3) -> int:
-        tasks = {}
-        for task_index in range(total_tasks):
-            task_dict = {"task_index": task_index, "task": f"Perform action {task_index}."}
-            tasks[task_index] = task_dict
-        return tasks
+    def _create_tasks(total_tasks: int = 3) -> Dataset:
+        ids = list(range(total_tasks))
+        tasks = [f"Perform action {i}." for i in ids]
+        return Dataset.from_dict({"task_index": ids, "task": tasks})
 
     return _create_tasks
 
@@ -196,6 +198,7 @@ def episodes_factory(tasks_factory):
     def _create_episodes(
         total_episodes: int = 3,
         total_frames: int = 400,
+        video_keys: list[str] | None = None,
         tasks: dict | None = None,
         multi_task: bool = False,
     ):
@@ -215,26 +218,41 @@ def episodes_factory(tasks_factory):
         # Generate random lengths that sum up to total_length
         lengths = np.random.multinomial(total_frames, [1 / total_episodes] * total_episodes).tolist()
 
-        tasks_list = [task_dict["task"] for task_dict in tasks.values()]
-        num_tasks_available = len(tasks_list)
+        num_tasks_available = len(tasks["task"])
 
-        episodes = {}
-        remaining_tasks = tasks_list.copy()
+        d = {
+            "episode_index": [],
+            "data/chunk_index": [],
+            "data/file_index": [],
+            "tasks": [],
+            "length": [],
+        }
+        if video_keys is not None:
+            for video_key in video_keys:
+                d[f"{video_key}/chunk_index"] = []
+                d[f"{video_key}/file_index"] = []
+
+        remaining_tasks = tasks["task"].copy()
         for ep_idx in range(total_episodes):
             num_tasks_in_episode = random.randint(1, min(3, num_tasks_available)) if multi_task else 1
-            tasks_to_sample = remaining_tasks if remaining_tasks else tasks_list
+            tasks_to_sample = remaining_tasks if remaining_tasks else tasks["task"]
             episode_tasks = random.sample(tasks_to_sample, min(num_tasks_in_episode, len(tasks_to_sample)))
             if remaining_tasks:
                 for task in episode_tasks:
                     remaining_tasks.remove(task)
 
-            episodes[ep_idx] = {
-                "episode_index": ep_idx,
-                "tasks": episode_tasks,
-                "length": lengths[ep_idx],
-            }
+            d["episode_index"].append(ep_idx)
+            # TODO(rcadene): remove heuristic of only one file
+            d["data/chunk_index"].append(0)
+            d["data/file_index"].append(0)
+            d["tasks"].append(episode_tasks)
+            d["length"].append(lengths[ep_idx])
+            if video_keys is not None:
+                for video_key in video_keys:
+                    d[f"{video_key}/chunk_index"].append(0)
+                    d[f"{video_key}/file_index"].append(0)
 
-        return episodes
+        return Dataset.from_dict(d)
 
     return _create_episodes
 
@@ -258,7 +276,7 @@ def hf_dataset_factory(features_factory, tasks_factory, episodes_factory, img_ar
         frame_index_col = np.array([], dtype=np.int64)
         episode_index_col = np.array([], dtype=np.int64)
         task_index = np.array([], dtype=np.int64)
-        for ep_dict in episodes.values():
+        for ep_dict in episodes:
             timestamp_col = np.concatenate((timestamp_col, np.arange(ep_dict["length"]) / fps))
             frame_index_col = np.concatenate((frame_index_col, np.arange(ep_dict["length"], dtype=int)))
             episode_index_col = np.concatenate(
@@ -291,7 +309,7 @@ def hf_dataset_factory(features_factory, tasks_factory, episodes_factory, img_ar
             },
             features=hf_features,
         )
-        dataset.set_transform(hf_transform_to_torch)
+        dataset.set_format("torch")
         return dataset
 
     return _create_hf_dataset
@@ -326,8 +344,9 @@ def lerobot_dataset_metadata_factory(
         if not tasks:
             tasks = tasks_factory(total_tasks=info["total_tasks"])
         if not episodes:
+            video_keys = [key for key, ft in info["features"].items() if ft["dtype"] == "video"]
             episodes = episodes_factory(
-                total_episodes=info["total_episodes"], total_frames=info["total_frames"], tasks=tasks
+                total_episodes=info["total_episodes"], total_frames=info["total_frames"], video_keys=video_keys, tasks=tasks
             )
 
         mock_snapshot_download = mock_snapshot_download_factory(
@@ -371,9 +390,9 @@ def lerobot_dataset_factory(
         multi_task: bool = False,
         info: dict | None = None,
         stats: dict | None = None,
-        episodes_stats: list[dict] | None = None,
-        tasks: list[dict] | None = None,
-        episode_dicts: list[dict] | None = None,
+        episodes_stats: datasets.Dataset | None = None,
+        tasks: datasets.Dataset | None = None,
+        episode_dicts: datasets.Dataset | None = None,
         hf_dataset: datasets.Dataset | None = None,
         **kwargs,
     ) -> LeRobotDataset:
@@ -388,9 +407,11 @@ def lerobot_dataset_factory(
         if not tasks:
             tasks = tasks_factory(total_tasks=info["total_tasks"])
         if not episode_dicts:
+            video_keys = [key for key, ft in info["features"].items() if ft["dtype"] == "video"]
             episode_dicts = episodes_factory(
                 total_episodes=info["total_episodes"],
                 total_frames=info["total_frames"],
+                video_keys=video_keys,
                 tasks=tasks,
                 multi_task=multi_task,
             )
diff --git a/tests/fixtures/files.py b/tests/fixtures/files.py
index 4ef12e49..32a689ec 100644
--- a/tests/fixtures/files.py
+++ b/tests/fixtures/files.py
@@ -7,83 +7,75 @@ import pyarrow.compute as pc
 import pyarrow.parquet as pq
 import pytest
 
+from datasets import Dataset
+
 from lerobot.common.datasets.utils import (
-    EPISODES_PATH,
-    EPISODES_STATS_PATH,
-    INFO_PATH,
-    STATS_PATH,
-    TASKS_PATH,
+    write_episodes,
+    write_episodes_stats,
+    write_hf_dataset,
+    write_info,
+    write_stats,
+    write_tasks,
 )
 
 
 @pytest.fixture(scope="session")
-def info_path(info_factory):
-    def _create_info_json_file(dir: Path, info: dict | None = None) -> Path:
+def create_info(info_factory):
+    def _create_info(dir: Path, info: dict | None = None):
         if not info:
             info = info_factory()
-        fpath = dir / INFO_PATH
-        fpath.parent.mkdir(parents=True, exist_ok=True)
-        with open(fpath, "w") as f:
-            json.dump(info, f, indent=4, ensure_ascii=False)
-        return fpath
+        write_info(info, dir)
 
-    return _create_info_json_file
+    return _create_info
 
 
 @pytest.fixture(scope="session")
-def stats_path(stats_factory):
-    def _create_stats_json_file(dir: Path, stats: dict | None = None) -> Path:
+def create_stats(stats_factory):
+    def _create_stats(dir: Path, stats: dict | None = None):
         if not stats:
             stats = stats_factory()
-        fpath = dir / STATS_PATH
-        fpath.parent.mkdir(parents=True, exist_ok=True)
-        with open(fpath, "w") as f:
-            json.dump(stats, f, indent=4, ensure_ascii=False)
-        return fpath
+        write_stats(stats, dir)
 
-    return _create_stats_json_file
+    return _create_stats
 
 
 @pytest.fixture(scope="session")
-def episodes_stats_path(episodes_stats_factory):
-    def _create_episodes_stats_jsonl_file(dir: Path, episodes_stats: list[dict] | None = None) -> Path:
+def create_episodes_stats(episodes_stats_factory):
+    def _create_episodes_stats(dir: Path, episodes_stats: Dataset | None = None):
         if not episodes_stats:
             episodes_stats = episodes_stats_factory()
-        fpath = dir / EPISODES_STATS_PATH
-        fpath.parent.mkdir(parents=True, exist_ok=True)
-        with jsonlines.open(fpath, "w") as writer:
-            writer.write_all(episodes_stats.values())
-        return fpath
+        write_episodes_stats(episodes_stats, dir)
 
-    return _create_episodes_stats_jsonl_file
+    return _create_episodes_stats
 
 
 @pytest.fixture(scope="session")
-def tasks_path(tasks_factory):
-    def _create_tasks_jsonl_file(dir: Path, tasks: list | None = None) -> Path:
+def create_tasks(tasks_factory):
+    def _create_tasks(dir: Path, tasks: Dataset | None = None):
         if not tasks:
             tasks = tasks_factory()
-        fpath = dir / TASKS_PATH
-        fpath.parent.mkdir(parents=True, exist_ok=True)
-        with jsonlines.open(fpath, "w") as writer:
-            writer.write_all(tasks.values())
-        return fpath
+        write_tasks(tasks, dir)
 
-    return _create_tasks_jsonl_file
+    return _create_tasks
 
 
 @pytest.fixture(scope="session")
-def episode_path(episodes_factory):
-    def _create_episodes_jsonl_file(dir: Path, episodes: list | None = None) -> Path:
+def create_episodes(episodes_factory):
+    def _create_episodes(dir: Path, episodes: Dataset | None = None):
         if not episodes:
             episodes = episodes_factory()
-        fpath = dir / EPISODES_PATH
-        fpath.parent.mkdir(parents=True, exist_ok=True)
-        with jsonlines.open(fpath, "w") as writer:
-            writer.write_all(episodes.values())
-        return fpath
+        write_episodes(episodes, dir)
 
-    return _create_episodes_jsonl_file
+    return _create_episodes
+
+@pytest.fixture(scope="session")
+def create_hf_dataset(hf_dataset_factory):
+    def _create_hf_dataset(dir: Path, hf_dataset: Dataset | None = None):
+        if not hf_dataset:
+            hf_dataset = hf_dataset_factory()
+        write_hf_dataset(hf_dataset, dir)
+
+    return _create_hf_dataset
 
 
 @pytest.fixture(scope="session")
@@ -91,6 +83,7 @@ def single_episode_parquet_path(hf_dataset_factory, info_factory):
     def _create_single_episode_parquet(
         dir: Path, ep_idx: int = 0, hf_dataset: datasets.Dataset | None = None, info: dict | None = None
     ) -> Path:
+        raise NotImplementedError()
         if not info:
             info = info_factory()
         if hf_dataset is None:
@@ -114,6 +107,7 @@ def multi_episode_parquet_path(hf_dataset_factory, info_factory):
     def _create_multi_episode_parquet(
         dir: Path, hf_dataset: datasets.Dataset | None = None, info: dict | None = None
     ) -> Path:
+        raise NotImplementedError()
         if not info:
             info = info_factory()
         if hf_dataset is None:
diff --git a/tests/fixtures/hub.py b/tests/fixtures/hub.py
index ae309cb4..c5fedf19 100644
--- a/tests/fixtures/hub.py
+++ b/tests/fixtures/hub.py
@@ -5,11 +5,12 @@ import pytest
 from huggingface_hub.utils import filter_repo_objects
 
 from lerobot.common.datasets.utils import (
-    EPISODES_PATH,
-    EPISODES_STATS_PATH,
+    DEFAULT_DATA_PATH,
+    DEFAULT_EPISODES_PATH,
+    DEFAULT_EPISODES_STATS_PATH,
+    DEFAULT_TASKS_PATH,
     INFO_PATH,
-    STATS_PATH,
-    TASKS_PATH,
+    LEGACY_STATS_PATH,
 )
 from tests.fixtures.constants import LEROBOT_TEST_DIR
 
@@ -17,17 +18,17 @@ from tests.fixtures.constants import LEROBOT_TEST_DIR
 @pytest.fixture(scope="session")
 def mock_snapshot_download_factory(
     info_factory,
-    info_path,
+    create_info,
     stats_factory,
-    stats_path,
+    create_stats,
     episodes_stats_factory,
-    episodes_stats_path,
+    create_episodes_stats,
     tasks_factory,
-    tasks_path,
+    create_tasks,
     episodes_factory,
-    episode_path,
-    single_episode_parquet_path,
+    create_episodes,
     hf_dataset_factory,
+    create_hf_dataset,
 ):
     """
     This factory allows to patch snapshot_download such that when called, it will create expected files rather
@@ -37,9 +38,9 @@ def mock_snapshot_download_factory(
     def _mock_snapshot_download_func(
         info: dict | None = None,
         stats: dict | None = None,
-        episodes_stats: list[dict] | None = None,
-        tasks: list[dict] | None = None,
-        episodes: list[dict] | None = None,
+        episodes_stats: datasets.Dataset | None = None,
+        tasks: datasets.Dataset | None = None,
+        episodes: datasets.Dataset | None = None,
         hf_dataset: datasets.Dataset | None = None,
     ):
         if not info:
@@ -59,14 +60,6 @@ def mock_snapshot_download_factory(
         if not hf_dataset:
             hf_dataset = hf_dataset_factory(tasks=tasks, episodes=episodes, fps=info["fps"])
 
-        def _extract_episode_index_from_path(fpath: str) -> int:
-            path = Path(fpath)
-            if path.suffix == ".parquet" and path.stem.startswith("episode_"):
-                episode_index = int(path.stem[len("episode_") :])  # 'episode_000000' -> 0
-                return episode_index
-            else:
-                return None
-
         def _mock_snapshot_download(
             repo_id: str,
             local_dir: str | Path | None = None,
@@ -79,40 +72,55 @@ def mock_snapshot_download_factory(
                 local_dir = LEROBOT_TEST_DIR
 
             # List all possible files
-            all_files = []
-            meta_files = [INFO_PATH, STATS_PATH, EPISODES_STATS_PATH, TASKS_PATH, EPISODES_PATH]
-            all_files.extend(meta_files)
-
-            data_files = []
-            for episode_dict in episodes.values():
-                ep_idx = episode_dict["episode_index"]
-                ep_chunk = ep_idx // info["chunks_size"]
-                data_path = info["data_path"].format(episode_chunk=ep_chunk, episode_index=ep_idx)
-                data_files.append(data_path)
-            all_files.extend(data_files)
+            all_files = [
+                INFO_PATH,
+                LEGACY_STATS_PATH,
+                # TODO(rcadene)
+                DEFAULT_TASKS_PATH.format(chunk_index=0, file_index=0),
+                DEFAULT_EPISODES_STATS_PATH.format(chunk_index=0, file_index=0),
+                DEFAULT_EPISODES_PATH.format(chunk_index=0, file_index=0),
+                DEFAULT_DATA_PATH.format(chunk_index=0, file_index=0),
+            ]
 
             allowed_files = filter_repo_objects(
                 all_files, allow_patterns=allow_patterns, ignore_patterns=ignore_patterns
             )
 
-            # Create allowed files
+            has_info = False
+            has_tasks = False
+            has_episodes = False
+            has_episodes_stats = False
+            has_stats = False
+            has_data = False
             for rel_path in allowed_files:
-                if rel_path.startswith("data/"):
-                    episode_index = _extract_episode_index_from_path(rel_path)
-                    if episode_index is not None:
-                        _ = single_episode_parquet_path(local_dir, episode_index, hf_dataset, info)
-                if rel_path == INFO_PATH:
-                    _ = info_path(local_dir, info)
-                elif rel_path == STATS_PATH:
-                    _ = stats_path(local_dir, stats)
-                elif rel_path == EPISODES_STATS_PATH:
-                    _ = episodes_stats_path(local_dir, episodes_stats)
-                elif rel_path == TASKS_PATH:
-                    _ = tasks_path(local_dir, tasks)
-                elif rel_path == EPISODES_PATH:
-                    _ = episode_path(local_dir, episodes)
+                if rel_path.startswith("meta/info.json"):
+                    has_info = True
+                elif rel_path.startswith("meta/stats"):
+                    has_stats = True
+                elif rel_path.startswith("meta/tasks"):
+                    has_tasks = True
+                elif rel_path.startswith("meta/episodes_stats"):
+                    has_episodes_stats = True
+                elif rel_path.startswith("meta/episodes"):
+                    has_episodes = True
+                elif rel_path.startswith("data/"):
+                    has_data = True
                 else:
-                    pass
+                    raise ValueError(f"{rel_path} not supported.")
+
+            if has_info:
+                create_info(local_dir, info)
+            if has_stats:
+                create_stats(local_dir, stats)
+            if has_tasks:
+                create_tasks(local_dir, tasks)
+            if has_episodes:
+                create_episodes(local_dir, episodes)
+            if has_episodes_stats:
+                create_episodes_stats(local_dir, episodes_stats)
+            if has_data:
+                create_hf_dataset(local_dir, hf_dataset)
+
             return str(local_dir)
 
         return _mock_snapshot_download