migrate-from-video-thumbnail

Migrate to cached_video_thumbnail

Converts one-shot video -> image calls from the video_thumbnail family into engine requests. This is an API and semantics migration: results become cache-owned files instead of caller-owned bytes/paths, failures become typed exceptions instead of nulls/booleans, and every call becomes cached, scheduled, and cancellable. Mapping tables: api-mapping.md.

Step 0 - inspect before touching anything

1. Identify the source package and its call sites:

   grep -rn "video_thumbnail\|get_thumbnail_video\|fc_native_video_thumbnail" pubspec.yaml lib/ test/
   grep -rn "thumbnailData\|thumbnailFile\|getVideoThumbnail\|ImageFormat\." lib/ test/
   

2. Verify the old package's actual API in the consumer's resolved version (.pub-cache) - forks differ in return types (String? vs XFile).
3. Platform gate: cached_video_thumbnail supports Android (minSdk 24) and iOS (13+) only. fc_native_video_thumbnail also runs on macOS and Windows; flutter_video_thumbnail_plus has a web path. If the app builds those targets, keep the old package behind a platform branch for them or stop and surface the gap - do not silently drop platforms.
4. WebP gate: ImageFormat.WEBP has no equivalent (by design; only jpeg/png). Find WebP consumers downstream (file extensions, MIME types, upload endpoints) before converting them to jpeg.
5. Note where old code passed a thumbnailPath/destFile it later reads, moves, uploads, or deletes - file ownership changes below.

Step 1 - dependencies

In pubspec.yaml: add cached_video_thumbnail: ^0.1.0 (needs Dart SDK ^3.12, Flutter >= 3.44). Keep the old dependency until Step 4 verifies, so the migration is revertible file-by-file; remove it as the final commit.

Step 2 - convert call sites

Core translation (full parameter tables in the reference file):

// OLD (video_thumbnail / get_thumbnail_video)
final bytes = await VideoThumbnail.thumbnailData(
  video: url, imageFormat: ImageFormat.JPEG,
  maxWidth: 128, quality: 25, timeMs: 2000);

// NEW - widget display: skip bytes entirely, use the provider
Image(image: VideoThumbnailImage(
  VideoSource.network(Uri.parse(url)),
  spec: const ThumbnailSpec(maxWidth: 128, quality: 25,
      position: Duration(milliseconds: 2000)),
))

// NEW - when a file/bytes value is genuinely needed
final thumb = await ThumbnailEngine.instance.getThumbnail(
  VideoSource.network(Uri.parse(url)),
  spec: const ThumbnailSpec(maxWidth: 128, quality: 25,
      position: Duration(milliseconds: 2000)),
);
// thumb.filePath is ENGINE-OWNED cache; copy out if the caller needs
// ownership, readAsBytes only if bytes are truly required.

Decision per call site:

• Rendered in a widget -> VideoThumbnailImage (adds ImageCache dedup and scroll cancellation for free). Prefer this whenever possible.
• Needs a path/bytes (upload, share, save) -> getThumbnail + copy out of thumb.filePath.
• The old video: parameter was a String for BOTH urls and local paths: route to VideoSource.network(Uri.parse(s)) vs VideoSource.file(s) explicitly (file paths must be absolute). Asset support is new (VideoSource.asset) - old code that copied assets to temp files first can drop that workaround entirely.

Step 3 - semantic diffs reviewers must sign off on

• Null/bool -> exceptions: == null / if (!ok) checks become try/catch on ThumbnailException (plus ArgumentError for structurally invalid input, thrown synchronously).
• Frame choice changes: old packages seek exactly (slow); the new default exact: false snaps to the nearest keyframe. Feeds should keep the fast default even though pixels may differ from before; use exact: true only where the precise frame matters.
• Quality clamps: 1..100 now; literal quality: 0 (seen with old PNG calls) throws ArgumentError - drop it, quality is ignored for PNG.
• Sizing: old maxWidth/maxHeight 0-defaults decoded full frames; new spec is a fit-within box in physical px that never upscales. Feeds should now SET a box (see the integrate-feed-thumbnails skill).
• Caching changes retry behavior: repeat calls become cache hits (wasCached: true); failures fast-fail for negativeCacheTtl (60s) - user-initiated retries should await engine.evict(source) first.
• Do not delete/move thumb.filePath: LRU owns it. Old cleanup code that deleted thumbnailPath outputs must be removed or pointed at copies.
• Headers are supported (VideoSource.network(headers: ...)) but excluded from cache identity; evict when content changes.

Step 4 - validate

1. dart analyze clean; dart format changed files.
2. Run the app's existing tests. Tests that mocked the old package's method channel must move to the injectable fake engine - invoke the mock-thumbnail-engine skill.
3. On-device smoke test: one asset, one file, one network thumbnail, plus one deliberate failure (bad URL) proving the error path renders.
4. Remove the old dependency; dart pub get; re-run analyze + tests.

Failure handling / rollback

• Already-migrated call sites are recognizable by ThumbnailEngine / VideoThumbnailImage usage - skip them idempotently.
• If a call site cannot be migrated (WebP contract, desktop platform), leave it on the old package, isolate it behind an adapter, and report it in the summary rather than forcing a broken conversion.
• Rollback = revert the migration commits; keeping the old dependency until final verification makes this a pure git operation.

Example scenario

"Replace get_thumbnail_video in our chat app; thumbnails for received videos are saved next to the media file." -> getThumbnail + explicit copy to the media dir (ownership), VideoThumbnailImage for the bubbles, try/catch replacing XFile-null checks, retry buttons call evict first, WebP check (chat used jpeg - safe), old package removed after tests pass.