scripts/segment_audio.py

"""Segment full meeting audio into sentence-level clips and write Parquet shards.

For each meeting in metadata.csv, this script:
  1. Parses the SRT file to get (start, end, text) segments.
  2. Uses ffmpeg to extract each segment from the opus file (stream copy, no re-encoding).
  3. Batches segments and writes Parquet shards with embedded audio bytes.

Usage:
    python -m scripts.segment_audio [--workers N] [--shard-size N] [--out-dir DIR]
"""

import argparse
import collections
import csv
import itertools
import re
import subprocess
from concurrent.futures import FIRST_COMPLETED, ProcessPoolExecutor, wait
from dataclasses import dataclass
from pathlib import Path

from rich.console import Console
from rich.progress import (
    BarColumn,
    MofNCompleteColumn,
    Progress,
    SpinnerColumn,
    TextColumn,
    TimeElapsedColumn,
    TimeRemainingColumn,
)

REPO_ROOT = Path(__file__).resolve().parent.parent
DEFAULT_SHARD_SIZE = 5000
DEFAULT_WORKERS = 4

console = Console()


@dataclass
class SrtSegment:
    index: int
    start_seconds: float
    end_seconds: float
    text: str


def _ts_to_seconds(ts: str) -> float:
    """Convert SRT timestamp (HH:MM:SS,mmm) to seconds."""
    h, m, rest = ts.split(":")
    s, ms = rest.split(",")
    return int(h) * 3600 + int(m) * 60 + int(s) + int(ms) / 1000


def parse_srt(srt_path: Path) -> list[SrtSegment]:
    """Parse an SRT file into a list of timed segments."""
    try:
        content = srt_path.read_text(encoding="utf-8")
    except FileNotFoundError:
        return []

    segments: list[SrtSegment] = []
    blocks = re.split(r"\n\s*\n", content.strip())

    for block in blocks:
        lines = block.strip().split("\n")
        if len(lines) < 3:
            continue

        try:
            idx = int(lines[0].strip())
        except ValueError:
            continue

        ts_match = re.match(
            r"(\d{2}:\d{2}:\d{2},\d{3})\s*-->\s*(\d{2}:\d{2}:\d{2},\d{3})",
            lines[1].strip(),
        )
        if not ts_match:
            continue

        start = _ts_to_seconds(ts_match.group(1))
        end = _ts_to_seconds(ts_match.group(2))
        text = " ".join(l.strip() for l in lines[2:] if l.strip())

        if not text or end <= start:
            continue

        segments.append(SrtSegment(index=idx, start_seconds=start, end_seconds=end, text=text))

    return segments


def extract_segment_audio(opus_path: Path, start: float, duration: float) -> bytes | None:
    """Extract a segment from an opus file using ffmpeg stream copy.

    Returns the raw OGG/Opus bytes, or None on failure.
    """
    cmd = [
        "ffmpeg",
        "-v", "error",
        "-ss", f"{start:.3f}",
        "-i", str(opus_path),
        "-t", f"{duration:.3f}",
        "-c", "copy",
        "-f", "ogg",
        "pipe:1",
    ]
    try:
        result = subprocess.run(cmd, capture_output=True, timeout=30)
        if result.returncode != 0:
            return None
        if len(result.stdout) < 100:
            return None
        return result.stdout
    except (subprocess.TimeoutExpired, OSError):
        return None


def process_meeting(row: dict) -> list[dict]:
    """Process a single meeting: parse SRT, extract all audio segments."""
    video_id = row["id"]
    opus_path = REPO_ROOT / row["audio"]
    srt_path = REPO_ROOT / row["subtitles"]

    if not opus_path.exists():
        return []

    segments = parse_srt(srt_path)
    if not segments:
        return []

    results = []
    for seg in segments:
        duration = seg.end_seconds - seg.start_seconds
        audio_bytes = extract_segment_audio(opus_path, seg.start_seconds, duration)
        if audio_bytes is None:
            continue

        results.append({
            "video_id": video_id,
            "segment_id": seg.index,
            "audio": {"bytes": audio_bytes, "path": f"{video_id}_{seg.index:05d}.opus"},
            "text": seg.text,
            "start_time": round(seg.start_seconds, 3),
            "end_time": round(seg.end_seconds, 3),
            "duration": round(duration, 3),
        })

    return results


def write_shard(segments: list[dict], shard_idx: int, out_dir: Path) -> Path:
    """Write a list of segment dicts as a Parquet shard with Audio feature."""
    from datasets import Audio, Dataset, Features, Value

    features = Features({
        "video_id": Value("string"),
        "segment_id": Value("int32"),
        "audio": Audio(),
        "text": Value("string"),
        "start_time": Value("float64"),
        "end_time": Value("float64"),
        "duration": Value("float64"),
    })

    ds = Dataset.from_dict(
        {k: [s[k] for s in segments] for k in segments[0]},
        features=features,
    )

    path = out_dir / f"train-{shard_idx:05d}.parquet"
    ds.to_parquet(path)
    return path


def _flush_buffer(buffer: collections.deque, shard_size: int, shard_idx: int,
                   out_dir: Path, *, force: bool = False) -> int:
    """Write complete shards from buffer. Returns updated shard_idx."""
    while len(buffer) >= shard_size or (force and buffer):
        n = min(shard_size, len(buffer))
        batch = [buffer.popleft() for _ in range(n)]
        shard_path = write_shard(batch, shard_idx, out_dir)
        console.print(
            f"  Wrote shard {shard_idx} ({n} segments) -> {shard_path.name}"
        )
        del batch
        shard_idx += 1
    return shard_idx


def main() -> None:
    parser = argparse.ArgumentParser(description="Segment audio and build Parquet shards")
    parser.add_argument("--workers", type=int, default=DEFAULT_WORKERS,
                        help="Number of parallel workers (default: %(default)s)")
    parser.add_argument("--shard-size", type=int, default=DEFAULT_SHARD_SIZE,
                        help="Segments per Parquet shard (default: %(default)s)")
    parser.add_argument("--out-dir", type=Path, default=REPO_ROOT / "segmented",
                        help="Output directory for Parquet shards")
    args = parser.parse_args()

    args.out_dir.mkdir(parents=True, exist_ok=True)

    src = REPO_ROOT / "metadata.csv"
    with open(src, encoding="utf-8", newline="") as f:
        reader = csv.DictReader(f)
        rows = list(reader)

    console.print(f"Processing {len(rows)} meetings with {args.workers} workers")
    console.print(f"Shard size: {args.shard_size} segments")
    console.print(f"Output: {args.out_dir}")

    buffer: collections.deque[dict] = collections.deque()
    shard_idx = 0
    total_segments = 0
    errors = 0
    meetings_done = 0
    max_in_flight = args.workers * 2

    progress = Progress(
        SpinnerColumn(),
        TextColumn("[progress.description]{task.description}"),
        BarColumn(),
        MofNCompleteColumn(),
        TimeElapsedColumn(),
        TimeRemainingColumn(),
        console=console,
    )

    with progress:
        task = progress.add_task("Meetings processed", total=len(rows))
        rows_iter = iter(rows)

        with ProcessPoolExecutor(max_workers=args.workers) as pool:
            active: dict = {}

            # Seed the pool with an initial batch of work
            for row in itertools.islice(rows_iter, max_in_flight):
                f = pool.submit(process_meeting, row)
                active[f] = row["id"]

            while active:
                done, _ = wait(active, return_when=FIRST_COMPLETED)

                for future in done:
                    video_id = active.pop(future)
                    try:
                        segments = future.result()
                        buffer.extend(segments)
                        total_segments += len(segments)
                        del segments
                    except Exception as e:
                        errors += 1
                        console.print(f"[red]Error processing {video_id}: {e}[/red]")

                    # Release the Future's internal result reference
                    future._result = None

                    meetings_done += 1
                    progress.advance(task)

                    # Submit next meeting to keep the pool fed
                    row = next(rows_iter, None)
                    if row is not None:
                        f = pool.submit(process_meeting, row)
                        active[f] = row["id"]

                # Flush complete shards after processing each batch of done futures
                shard_idx = _flush_buffer(
                    buffer, args.shard_size, shard_idx, args.out_dir
                )

    # Flush remaining segments
    shard_idx = _flush_buffer(
        buffer, args.shard_size, shard_idx, args.out_dir, force=True
    )

    console.print(f"\n[bold green]Done![/bold green]")
    console.print(f"  Total segments: {total_segments}")
    console.print(f"  Total shards:   {shard_idx}")
    console.print(f"  Errors:         {errors}")


if __name__ == "__main__":
    main()