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"""Visualize pixel-level differences between two videos."""
from __future__ import annotations
import argparse
import csv
import json
import subprocess
from pathlib import Path
import numpy as np
def run_json(cmd: list[str]) -> dict:
out = subprocess.check_output(cmd, text=True)
return json.loads(out)
def probe_video(path: Path) -> dict:
data = run_json(
[
"ffprobe",
"-v",
"error",
"-select_streams",
"v:0",
"-show_entries",
"stream=width,height,avg_frame_rate,nb_frames,duration",
"-of",
"json",
str(path),
]
)
stream = data["streams"][0]
return {
"width": int(stream["width"]),
"height": int(stream["height"]),
"avg_frame_rate": stream.get("avg_frame_rate", "0/1"),
"nb_frames": int(stream["nb_frames"]) if stream.get("nb_frames", "N/A").isdigit() else None,
"duration": float(stream.get("duration", 0.0)),
}
def parse_rate(rate: str) -> float:
num, den = rate.split("/")
return float(num) / float(den)
def open_reader(path: Path, width: int, height: int, fps: float | None = None, align: bool = False) -> subprocess.Popen:
cmd = [
"ffmpeg",
"-v",
"error",
"-i",
str(path),
]
if align:
if fps is None:
raise ValueError("fps is required when align=True")
cmd += ["-vf", f"scale={width}:{height}:flags=bicubic,fps={fps:.6f}"]
cmd += [
"-f",
"rawvideo",
"-pix_fmt",
"rgb24",
"-",
]
return subprocess.Popen(
cmd,
stdout=subprocess.PIPE,
)
def open_writer(path: Path, width: int, height: int, fps: float) -> subprocess.Popen:
return subprocess.Popen(
[
"ffmpeg",
"-y",
"-v",
"error",
"-f",
"rawvideo",
"-pix_fmt",
"rgb24",
"-s",
f"{width}x{height}",
"-r",
f"{fps:.6f}",
"-i",
"-",
"-an",
"-pix_fmt",
"yuv420p",
"-c:v",
"mpeg4",
"-q:v",
"2",
str(path),
],
stdin=subprocess.PIPE,
)
def read_frame(proc: subprocess.Popen, frame_bytes: int) -> bytes | None:
assert proc.stdout is not None
data = proc.stdout.read(frame_bytes)
if len(data) == 0:
return None
if len(data) != frame_bytes:
raise RuntimeError(f"Short frame read: expected {frame_bytes} bytes, got {len(data)}")
return data
def close_proc(proc: subprocess.Popen) -> None:
try:
proc.wait(timeout=5)
except subprocess.TimeoutExpired:
proc.kill()
proc.wait()
def make_heatmap(diff_mag: np.ndarray, changed: np.ndarray, show_all_diffs: bool) -> np.ndarray:
heat = np.zeros((*diff_mag.shape, 3), dtype=np.uint8)
visible_diff = diff_mag if show_all_diffs else np.where(changed, diff_mag, 0)
heat[..., 0] = visible_diff
heat[..., 1] = np.where(changed, np.clip(diff_mag // 3, 0, 255), 0).astype(np.uint8)
return heat
def compare_videos(args: argparse.Namespace) -> None:
original = args.original.resolve()
edited = args.edited.resolve()
output_dir = args.output_dir.resolve()
output_dir.mkdir(parents=True, exist_ok=True)
original_info = probe_video(original)
edited_info = probe_video(edited)
width = original_info["width"]
height = original_info["height"]
fps = parse_rate(original_info["avg_frame_rate"])
mismatch = (width, height) != (edited_info["width"], edited_info["height"])
fps_mismatch = original_info["avg_frame_rate"] != edited_info["avg_frame_rate"]
if (mismatch or fps_mismatch) and not args.align_edited_to_original:
raise ValueError(
"Video geometry mismatch. For strict pixel-by-pixel comparison, compare a final composited video "
"with the same resolution and fps as the original. To inspect a raw model output anyway, rerun with "
f"--align-edited-to-original. original={original_info}, edited={edited_info}"
)
frame_bytes = width * height * 3
max_frames = args.max_frames
if max_frames is None:
candidates = [original_info["nb_frames"]]
if not args.align_edited_to_original:
candidates.append(edited_info["nb_frames"])
candidates = [v for v in candidates if v is not None]
max_frames = min(candidates) if candidates else 10**12
reader_a = open_reader(original, width, height)
reader_b = open_reader(edited, width, height, fps=fps, align=args.align_edited_to_original)
writers = {
"changed_mask": open_writer(output_dir / "changed_mask.mp4", width, height, fps),
"diff_heatmap": open_writer(output_dir / "diff_heatmap.mp4", width, height, fps),
"diff_overlay": open_writer(output_dir / "diff_overlay.mp4", width, height, fps),
}
rows: list[dict[str, int | float]] = []
total_changed = 0
total_pixels = 0
threshold = args.threshold
try:
for frame_index in range(max_frames):
raw_a = read_frame(reader_a, frame_bytes)
raw_b = read_frame(reader_b, frame_bytes)
if raw_a is None or raw_b is None:
break
a = np.frombuffer(raw_a, dtype=np.uint8).reshape((height, width, 3))
b = np.frombuffer(raw_b, dtype=np.uint8).reshape((height, width, 3))
absdiff = np.abs(a.astype(np.int16) - b.astype(np.int16)).astype(np.uint8)
diff_mag = absdiff.max(axis=2)
changed = diff_mag > threshold
changed_count = int(changed.sum())
total_changed += changed_count
total_pixels += width * height
mask_rgb = np.repeat((changed.astype(np.uint8) * 255)[:, :, None], 3, axis=2)
heat = make_heatmap(diff_mag, changed, args.heatmap_all_diffs)
overlay = a.copy()
overlay[changed] = (overlay[changed].astype(np.uint16) // 3 + np.array([170, 0, 0], dtype=np.uint16)).clip(0, 255).astype(np.uint8)
assert writers["changed_mask"].stdin is not None
assert writers["diff_heatmap"].stdin is not None
assert writers["diff_overlay"].stdin is not None
writers["changed_mask"].stdin.write(mask_rgb.tobytes())
writers["diff_heatmap"].stdin.write(heat.tobytes())
writers["diff_overlay"].stdin.write(overlay.tobytes())
rows.append(
{
"frame": frame_index,
"changed_pixels": changed_count,
"total_pixels": width * height,
"changed_ratio": changed_count / (width * height),
"mean_abs_diff": float(absdiff.mean()),
"max_abs_diff": int(absdiff.max()),
}
)
finally:
for writer in writers.values():
if writer.stdin is not None:
writer.stdin.close()
close_proc(writer)
close_proc(reader_a)
close_proc(reader_b)
with (output_dir / "per_frame_stats.csv").open("w", newline="", encoding="utf-8") as handle:
fieldnames = ["frame", "changed_pixels", "total_pixels", "changed_ratio", "mean_abs_diff", "max_abs_diff"]
writer = csv.DictWriter(handle, fieldnames=fieldnames)
writer.writeheader()
writer.writerows(rows)
summary = {
"original": str(original),
"edited": str(edited),
"original_info": original_info,
"edited_info": edited_info,
"threshold": threshold,
"heatmap_all_diffs": args.heatmap_all_diffs,
"align_edited_to_original": args.align_edited_to_original,
"compared_frames": len(rows),
"changed_pixels": total_changed,
"total_pixels": total_pixels,
"changed_ratio": total_changed / total_pixels if total_pixels else 0.0,
"outputs": {
"changed_mask": str(output_dir / "changed_mask.mp4"),
"diff_heatmap": str(output_dir / "diff_heatmap.mp4"),
"diff_overlay": str(output_dir / "diff_overlay.mp4"),
"per_frame_stats": str(output_dir / "per_frame_stats.csv"),
},
}
(output_dir / "summary.json").write_text(json.dumps(summary, indent=2), encoding="utf-8")
print(json.dumps(summary, indent=2))
def parse_args() -> argparse.Namespace:
parser = argparse.ArgumentParser(description="Create pixel-level video difference visualizations.")
parser.add_argument("--original", type=Path, required=True)
parser.add_argument("--edited", type=Path, required=True)
parser.add_argument("--output-dir", type=Path, required=True)
parser.add_argument("--threshold", type=int, default=2, help="Per-channel max RGB diff threshold before a pixel counts as changed.")
parser.add_argument(
"--heatmap-all-diffs",
action="store_true",
help="Show every nonzero diff in diff_heatmap. By default, diff_heatmap only shows pixels above --threshold.",
)
parser.add_argument("--max-frames", type=int)
parser.add_argument(
"--align-edited-to-original",
action="store_true",
help="Scale and resample the edited video to the original resolution/fps before comparing. Use for raw model outputs.",
)
return parser.parse_args()
if __name__ == "__main__":
compare_videos(parse_args())
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