docs: add teaching examples and video project

show/video/verify.py

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+"""Check rendered media, matching captions, and frozen benchmark provenance."""
+import argparse
+import hashlib
+import json
+from pathlib import Path
+
+import av
+
+HERE = Path(__file__).resolve().parent
+parser = argparse.ArgumentParser()
+parser.add_argument('--quality', default='final', choices=['preview', 'final'])
+parser.add_argument('--scene', default='SlimeFilm')
+args = parser.parse_args()
+name = f'{args.scene}-{args.quality}'
+report = json.loads((HERE / f'output/{name}.render.json').read_text())
+timeline = json.loads((HERE / f'output/{name}.timeline.json').read_text())
+for source, digest in report['source_sha256'].items():
+    assert hashlib.sha256((HERE/source).read_bytes()).hexdigest() == digest, f'changed after render: {source}'
+data = json.loads((HERE/'data/benchmarks.json').read_text())
+for record in (data,):
+    path = HERE/record['source']
+    assert hashlib.sha256(path.read_bytes()).hexdigest() == record['source_sha256'], f'benchmark source changed: {path}'
+for cue in timeline['cues']:
+    assert 0 <= cue['start'] < cue['end'] <= timeline['duration']+.1
+for a,b in zip(timeline['cues'],timeline['cues'][1:]):
+    assert a['end'] <= b['start']+.01, 'overlapping captions'
+assert len(timeline['cues']) == report['caption_count']
+with av.open(str(HERE/'output'/report['file'])) as container:
+    stream = container.streams.video[0]
+    expected = (854,480) if args.quality == 'preview' else (1920,1080)
+    assert (stream.width,stream.height) == expected
+    duration = float(stream.duration*stream.time_base)
+    assert abs(duration-timeline['duration']) < .15, 'video and caption timelines differ'
+    frames = sum(1 for _ in container.decode(stream))
+    assert frames > 0
+print(f'OK: {report["file"]}; {frames} decoded frames; {len(timeline["cues"])} captions; source hashes match')