"""Stream-copy an .mkv into an .mp4 so Discord can play it inline (no re-encode)."""
import subprocess
from pathlib import Path


def remux_to_mp4(src: Path, dst: Path, timeout: int = 1800) -> bool:
    cmd = [
        "ffmpeg", "-v", "error", "-y", "-i", str(src),
        "-map", "0:v", "-map", "0:a?", "-c", "copy",
        "-movflags", "+faststart", str(dst),
    ]
    try:
        result = subprocess.run(cmd, capture_output=True, timeout=timeout)
        ok = result.returncode == 0 and dst.exists() and dst.stat().st_size > 0
    except (OSError, subprocess.TimeoutExpired):
        ok = False
    if not ok:
        dst.unlink(missing_ok=True)
    return ok