feat(encode-comparison): encode middle clip across CRF values

encode_comparison.py

@@ -0,0 +1,77 @@
+#!/usr/bin/env python3.11
+import argparse
+import logging
+import subprocess
+from pathlib import Path
+
+
+def parse_args() -> argparse.Namespace:
+    parser = argparse.ArgumentParser(
+        description="Encode middle 1-min slice of video with multiple CRF values.",
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
+    )
+    parser.add_argument("video", type=Path, help="Input video file")
+    parser.add_argument("--codec", choices=["x264", "x265"], default="x265", help="Codec to use")
+    parser.add_argument("--crf", nargs="+", type=int, default=[15, 20, 25, 30, 35, 40], help="CRF values")
+    return parser.parse_args()
+
+
+def read_video_duration(video_path: Path) -> float:
+    cmd = [
+        "ffprobe",
+        "-v",
+        "error",
+        "-show_entries",
+        "format=duration",
+        "-of",
+        "default=noprint_wrappers=1:nokey=1",
+        str(video_path),
+    ]
+    result = subprocess.run(cmd, capture_output=True, text=True, check=True)
+    return float(result.stdout.strip())
+
+
+def encode_clip(clip_path: Path, codec: str, crf: int, out_path: Path) -> Path:
+    # clip_path is actually the input video, we encode the middle slice on the fly
+    total_duration = read_video_duration(clip_path)
+    slice_duration = 60
+    start = max(0, int(total_duration // 2 - slice_duration // 2))
+    if codec == "x264":
+        lib = "h264_videotoolbox"
+    else:
+        lib = "hevc_videotoolbox"
+    cmd = [
+        "ffmpeg",
+        "-y",
+        "-ss",
+        str(start),
+        "-t",
+        str(slice_duration),
+        "-i",
+        str(clip_path),
+        "-c:v",
+        lib,
+        "-q:v",
+        str(crf),
+        "-preset",
+        "medium",
+        "-c:a",
+        "copy",
+        str(out_path),
+    ]
+    logging.info(f"Encoding {out_path.name} with {lib} q:v={crf} (hwaccel) from middle slice")
+    subprocess.run(cmd, check=True)
+
+
+def main():
+    logging.basicConfig(level=logging.INFO, format="%(asctime)s %(levelname)s: %(message)s")
+    args = parse_args()
+    outdir = args.video.parent
+    outdir.mkdir(parents=True, exist_ok=True)
+    for crf in args.crf:
+        out_path = outdir / f"{args.video.stem}.{args.codec}_crf{crf}.mp4"
+        encode_clip(clip_path=args.video, codec=args.codec, crf=crf, out_path=out_path)
+
+
+if __name__ == "__main__":
+    main()