fix(example-images): read real dimensions for imported videos, fixes #1115

Example videos added through the "Add examples" flow were stored with a
hardcoded 720x1280 entry. The dimension probe next to it only ran for
images (PIL cannot open .mp4/.webm files), so every video entry stayed
portrait regardless of the source. The showcase viewer then sizes its
container straight from that value (--media-aspect in showcase.css), so
landscape clips were letterboxed inside a 9:16 box. CivitAI-sourced
examples were unaffected because their dimensions come from the API.

PIL cannot read video containers, so add a dependency-free reader that
parses the container headers instead: moov/trak/tkhd for ISO base media
(with the sample description as a fallback), Segment/Tracks/Pixel* for
WebM/Matroska, and RIFF/WebP for animated examples saved with a video
extension. The sniffed signature decides which reader runs, so a .mp4
that is really WebM still reports the right size; the extension is only
a fallback. Both readers seek past mdat rather than reading it, so a
large file costs the same as a small one.

Imported entries now record the file's real size and keep the previous
placeholder only when the file cannot be parsed.

Existing libraries keep their wrong entries, so backfill them once via
the existing naming migration: bump CURRENT_NAMING_VERSION to 3 and
repair each model's empty-url entries from the files on disk, then sync
the scanner cache. Only entries with no remote url are touched -- those
have no other source, which makes the rewrite lossless -- and entries
already carrying the right size are left byte-identical, so the pass is
idempotent and a no-op for libraries that never imported a video.

tests/utils/test_example_images_migration.py

@@ -177,3 +177,156 @@ async def test_migrations_run_and_update_progress(tmp_path, monkeypatch):
     update_args = lora_scanner.update_calls[0]
     assert update_args[0] == str(metadata_path)
     assert update_args[2]["civitai"]["customImages"][0]["id"] == "short1234"
+
+
+@pytest.mark.asyncio
+async def test_v2_to_v3_migration_repairs_video_dimensions(tmp_path, monkeypatch):
+    """Upgrading a library already at v2 backfills local video dimensions once.
+
+    This mirrors the real upgrade path for issue #1115: the naming migration is
+    already done, but imported videos still carry the 720x1280 placeholder.
+    """
+
+    from tests.utils.test_video_dimension_probe import build_mp4
+
+    example_root = tmp_path / "example_images"
+    library_root = example_root / "main"
+    library_root.mkdir(parents=True)
+
+    progress_path = library_root / ".download_progress.json"
+    progress_path.write_text(json.dumps({"naming_version": 2}))
+
+    model_hash = "d" * 64
+    model_folder = library_root / model_hash
+    model_folder.mkdir()
+    # Landscape clip stored during the buggy import path.
+    (model_folder / "custom_land1.mp4").write_bytes(build_mp4(1280, 720))
+
+    model_file = tmp_path / "models" / "video.safetensors"
+    model_file.parent.mkdir()
+    model_file.write_text("weights", encoding="utf-8")
+
+    scanner = FakeScanner(
+        {
+            model_hash: {
+                "sha256": model_hash,
+                "file_path": str(model_file),
+                "civitai": {
+                    "images": [
+                        {"url": "https://example.com/remote.jpg", "type": "image", "width": 512, "height": 512}
+                    ],
+                    "customImages": [
+                        {"url": "", "id": "land1", "type": "video", "width": 720, "height": 1280}
+                    ],
+                },
+            }
+        }
+    )
+
+    async def fake_get_lora_scanner(cls):
+        return scanner
+
+    async def fake_get_checkpoint_scanner(cls):
+        return FakeScanner({})
+
+    monkeypatch.setattr(
+        migration_module.ServiceRegistry, "get_lora_scanner", classmethod(fake_get_lora_scanner)
+    )
+    monkeypatch.setattr(
+        migration_module.ServiceRegistry,
+        "get_checkpoint_scanner",
+        classmethod(fake_get_checkpoint_scanner),
+    )
+
+    monkeypatch.setattr(
+        migration_module.settings,
+        "get",
+        lambda key, default=None: str(example_root) if key == "example_images_path" else default,
+    )
+    monkeypatch.setattr(
+        migration_module,
+        "iter_library_roots",
+        lambda: [("main", str(library_root))],
+    )
+
+    saved_metadata = []
+
+    async def fake_save_metadata(path, metadata):
+        saved_metadata.append((path, metadata))
+        return True
+
+    async def fake_load_payload(path):
+        return {
+            "model_name": "Video",
+            "civitai": {
+                "images": [
+                    {"url": "https://example.com/remote.jpg", "type": "image", "width": 512, "height": 512}
+                ],
+                "customImages": [
+                    {"url": "", "id": "land1", "type": "video", "width": 720, "height": 1280}
+                ],
+            },
+        }
+
+    monkeypatch.setattr(
+        migration_module.MetadataManager, "save_metadata", staticmethod(fake_save_metadata)
+    )
+    monkeypatch.setattr(
+        migration_module.MetadataManager, "load_metadata_payload", staticmethod(fake_load_payload)
+    )
+
+    scheduled = []
+    original_create_task = asyncio.create_task
+
+    def capture_create_task(coro, *args, **kwargs):
+        task = original_create_task(coro, *args, **kwargs)
+        scheduled.append(task)
+        return task
+
+    monkeypatch.setattr(migration_module.asyncio, "create_task", capture_create_task)
+
+    await migration_module.ExampleImagesMigration.check_and_run_migrations()
+    await asyncio.gather(*scheduled)
+
+    assert len(saved_metadata) == 1
+    _path, payload = saved_metadata[0]
+    entry = payload["civitai"]["customImages"][0]
+    assert (entry["width"], entry["height"]) == (1280, 720)
+    # Remote-backed entry is untouched.
+    assert payload["civitai"]["images"][0]["width"] == 512
+
+    assert json.loads(progress_path.read_text())["naming_version"] == 3
+
+
+@pytest.mark.asyncio
+async def test_v3_migration_does_not_run_twice(tmp_path, monkeypatch):
+    """The version gate keeps the repair off the startup path after one run."""
+
+    example_root = tmp_path / "example_images"
+    library_root = example_root / "main"
+    library_root.mkdir(parents=True)
+    (library_root / ".download_progress.json").write_text(json.dumps({"naming_version": 3}))
+
+    monkeypatch.setattr(
+        migration_module.settings,
+        "get",
+        lambda key, default=None: str(example_root) if key == "example_images_path" else default,
+    )
+    monkeypatch.setattr(
+        migration_module,
+        "iter_library_roots",
+        lambda: [("main", str(library_root))],
+    )
+
+    called = []
+
+    async def spy_run_migrations(*args, **kwargs):
+        called.append(args)
+
+    monkeypatch.setattr(
+        migration_module.ExampleImagesMigration, "run_migrations", staticmethod(spy_run_migrations)
+    )
+
+    await migration_module.ExampleImagesMigration.check_and_run_migrations()
+
+    assert called == []