feat:v3.0 to v2.1 (and v2.1 to v2.0)

[bingogome]

What this does

It converts back from v3.0 dataset to v2.1 in case you need back compatibility.

Examples:

Title	Label
Fixes #[issue]	(🐛 Bug)
Adds new dataset	(🗃️ Dataset)
Optimizes something	(⚡️ Performance)

How it was tested

Convert a dataset and visualize it using lerobot tools to confirm data validity.

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[Copilot]

Pull Request Overview

This PR adds functionality to convert LeRobot datasets from v3.0 format back to v2.1 format for backward compatibility. This is the reverse operation of the existing v2.1 to v3.0 conversion.

• Adds a new conversion script that transforms the consolidated v3.0 file layout back to the legacy per-episode structure of v2.1
• Implements reverse transformations for data files, video files, metadata, and configuration
• Provides command-line interface for dataset conversion with options for local directories and force conversion

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[5hadytru]

Hey y'all; thanks for the useful script! I ran into a bug (in the context of fine-tuning GR00T-N1.5-3B with the Isaac-GR00T repo) which I fixed by making the following changes to the v2.1-converted dataset's info.json. Old lines:

"data_path": "data/chunk-{chunk_index:03d}/episode_{episode_index:06d}.parquet",
"video_path": "videos/chunk-{chunk_index:03d}/{video_key}/episode_{episode_index:06d}.mp4",

New lines:

"data_path": "data/chunk-{episode_chunk:03d}/episode_{episode_index:06d}.parquet",
"video_path": "videos/chunk-{episode_chunk:03d}/{video_key}/episode_{episode_index:06d}.mp4",

And for stats.json, I removed the "count" entry for the "action" and "observation.state" entries. This now matches actual v2.1 metadata sufficiently for GR00T fine-tuning. I believe y'all need to change the "LEGACY_DATA_PATH_TEMPLATE" and "LEGACY_VIDEO_PATH_TEMPLATE" variables in y'all's script + probably something else.

[bingogome]

You probably also need a script from v2.1 to v2.0: checkout here.

[sumanth-nirmal]

Thanks for the converstion script, this will be really helpful as currently Nvidia Groot N1.5 expects the LeRobot format to be v2.1. However, can you also add support to convert the data sets locally from V3.0 to V2.1 instead of only supporting the datasets uploaded to Hugging Face?