extract_frames.py

"""
Extract frames from the Motive Loop Closure Dataset raw video clips.

Usage:
  # Extract all sequences at 2 fps (default)
  python3 extract_frames.py

  # Extract a specific sequence
  python3 extract_frames.py --sequence v102_20260909_loop01

  # Custom frame rate and output root
  python3 extract_frames.py --fps 5 --frames-root ./frames_5fps

Outputs frames to:
  data/<sequence_id>/<role>/frames/<fps>fps/000001.jpg ...

Requirements: ffmpeg must be on PATH
"""
from __future__ import annotations
import argparse, subprocess, sys
from pathlib import Path

SCRIPT_DIR    = Path(__file__).parent
VIDEOS_DIR    = SCRIPT_DIR / "videos"
DATA_DIR      = SCRIPT_DIR / "data"
CLIP_DURATION = 180  # seconds


def extract(mp4: Path, out_dir: Path, fps: int):
    out_dir.mkdir(parents=True, exist_ok=True)
    existing = list(out_dir.glob("*.jpg"))
    if existing:
        print(f"    {out_dir.name}/ already has {len(existing)} frames — skipping")
        return len(existing)
    cmd = [
        "ffmpeg", "-y", "-i", str(mp4),
        "-vf", f"fps={fps}",
        "-q:v", "3",
        str(out_dir / "%06d.jpg"),
    ]
    result = subprocess.run(cmd, capture_output=True)
    if result.returncode != 0:
        print(f"    ERROR: ffmpeg failed:\n{result.stderr.decode()[-300:]}")
        return 0
    n = len(list(out_dir.glob("*.jpg")))
    print(f"    → {n} frames")
    return n


def main():
    ap = argparse.ArgumentParser(description=__doc__,
                                 formatter_class=argparse.RawDescriptionHelpFormatter)
    ap.add_argument("--fps",         type=int, default=2)
    ap.add_argument("--sequence",    default=None, help="Extract only this sequence")
    ap.add_argument("--frames-root", default=None,
                    help="Root for frame output (default: data/<seq>/<role>/frames/<fps>fps/)")
    args = ap.parse_args()

    sequences = sorted(DATA_DIR.iterdir()) if DATA_DIR.exists() else []
    if args.sequence:
        sequences = [DATA_DIR / args.sequence]

    total_frames = 0
    for seq_dir in sequences:
        if not seq_dir.is_dir():
            continue
        print(f"\n[{seq_dir.name}]")
        for role in ("origin", "revisit"):
            role_dir = seq_dir / role
            if not role_dir.exists():
                continue
            # Find the mp4 in videos/
            # filename pattern: v{vehicle}_{role}_{YYYYMMDD_HHMMSS}_front_facing.mp4
            parts = seq_dir.name.split("_")          # v102, 20260909, loop01
            vehicle = parts[0][1:]                   # "102"
            date    = parts[1]                       # "20260909"
            mp4s = sorted(VIDEOS_DIR.glob(f"v{vehicle}_{role}_*_front_facing.mp4"))
            # Match by date
            mp4s = [m for m in mp4s if date in m.name]
            if not mp4s:
                print(f"  [{role}] no MP4 found in videos/ — download it first")
                continue
            mp4 = mp4s[0]
            if args.frames_root:
                out_dir = Path(args.frames_root) / seq_dir.name / role
            else:
                out_dir = role_dir / "frames" / f"{args.fps}fps"
            print(f"  [{role}] {mp4.name} @ {args.fps} fps")
            total_frames += extract(mp4, out_dir, args.fps)

    print(f"\nDone. {total_frames:,} frames extracted.")


if __name__ == "__main__":
    main()