feat(dataset tools): add trim_episode_start operation

[pkooij]

Title

feat(datasets): add trim_episode_start edit operation

Type / Scope

• Type: Feature
• Scope: datasets, scripts

Summary / Motivation

This PR adds a new dataset edit operation, trim_episode_start, to remove the first N seconds from episodes while keeping dataset invariants intact (frame indices, global indices, episode metadata, and stats). This is useful for removing startup/warm-up frames from collected data without manual dataset surgery. It also skips episodes that are too short to trim, so one short episode does not fail the full run.

Related issues

• Fixes / Closes: N/A
• Related: N/A

What changed

• Added trim_episode_start(...) in src/lerobot/datasets/dataset_tools.py.
• Added trim_episode_start operation wiring in src/lerobot/scripts/lerobot_edit_dataset.py.
• Added parser coverage for the new operation in tests/scripts/test_edit_dataset_parsing.py.
• Added trim behavior tests in tests/datasets/test_dataset_tools.py:
  • metadata/index consistency after trimming,
  • skipping too-short episodes,
  • failure when all selected episodes are too short.
• Video behavior: this operation currently performs logical trimming for videos by updating per-episode video timestamps in metadata; it does not re-encode/cut MP4 files.

Breaking changes: none.

How was this tested (or how to run locally)

• Tests added:

  • tests/datasets/test_dataset_tools.py
  • tests/scripts/test_edit_dataset_parsing.py

• Syntax checks run:

  python -m py_compile src/lerobot/datasets/dataset_tools.py src/lerobot/scripts/lerobot_edit_dataset.py tests/datasets/test_dataset_tools.py tests/scripts/test_edit_dataset_parsing.py

• Suggested local test run:

  pytest -q tests/scripts/test_edit_dataset_parsing.py tests/datasets/test_dataset_tools.py -k trim_episode_start

• Example CLI usage:

  python -m lerobot.scripts.lerobot_edit_dataset \
    --repo_id lerobot-data-collection/level2_final_quality3 \
    --new_repo_id lerobot-data-collection/level2_final_quality3_trim3s \
    --operation.type trim_episode_start \
    --operation.seconds 3.0

Checklist (required before merge)

• Linting/formatting run (pre-commit run -a)
• All tests pass locally (pytest)
• Documentation updated
• CI is green

Reviewer notes

• Please focus review on trim_episode_start index/metadata invariants and the skip-too-short behavior.
• Video handling is metadata-based (no video re-encoding); this preserves correctness for loading but does not reduce video file size.
• Anyone in the community is free to review the PR.

[s1lent4gnt]

It might be worth checking this work as well since it has the same intended use: #3024