feat: YouTube-style seek indicator for keyboard seeking

[Ortes]

What

Adds a YouTube-style seek indicator that flashes on screen when the user seeks with the keyboard arrows on the desktop controls (MaterialDesktopControls).

• Pressing → / ← shows a small pill with a directional icon and the amount seeked.
• Repeated presses in the same direction keep the pill visible and accumulate the total (e.g. 10s → 20s → 30s), just like YouTube.
• Pressing the opposite direction (or after the pill fades ~0.9s) resets the counter.

How

• New reusable widget lib/src/seek_indicator.dart (fades via AnimatedOpacity, mirrors the existing CenterSeekButton style; purely visual — wrapped in IgnorePointer).
• _MaterialDesktopControlsState accumulates the seeked seconds in _seekForward/_seekBackward (kept in sync with the existing Duration seek step) and auto-hides via a Timer, mirroring the existing buffering-indicator pattern.
• Gated by a new ChewieController.showSeekIndicator option (default true), wired through copyWith.

Tests

test/seek_indicator_test.dart covers accumulation on repeated presses, direction reset, auto fade-out, the showSeekIndicator: false opt-out, and the option default/copyWith.

dart format, flutter analyze lib test, and the full flutter test suite are clean.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.73%. Comparing base (e776ce7) to head (7fb5885).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #953      +/-   ##
==========================================
+ Coverage   71.68%   72.73%   +1.05%     
==========================================
  Files          40       41       +1     
  Lines        2518     2560      +42     
==========================================
+ Hits         1805     1862      +57     
+ Misses        713      698      -15     

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[Ortes]

Hi @diegotori 👋

Beyond this PR, I'd like to offer to help with maintenance on chewie if you're open to it.

A bit of context:

• I've had PRs merged here before (Add keyboard controls seek forward and backward and fullscreen escape on desktop #876 desktop keyboard controls, Fix example on web #910 web example fix), and just opened three more, each with tests, a CHANGELOG entry and green CI: feat: YouTube-style seek indicator for keyboard seeking #953 (keyboard seek indicator), feat: auto-hide the mouse cursor while idle in fullscreen #954 (auto-hide cursor in fullscreen), feat: toggle fullscreen with the F key on desktop #955 (F-key fullscreen toggle).
• I use chewie in production at my company, and also personally on a daily/weekly basis inside a custom movie player I built on top of it — so I'm exercising it heavily across web and mobile.

I know the open-PR queue is long, and I'd be glad to take some of that load off you: triaging and reviewing PRs, keeping the package current with new Flutter releases, and helping land fixes. Would you be open to adding me as a co-maintainer (or triage access to start)? Happy to do whatever works best for you and the Flutter Community org.

Either way, thanks for maintaining this 🙏

[diegotori]

@Ortes please fix the conflicts here. Thanks.

[Ortes]

Heads-up: #964 is stacked on this branch — it extracts the indicator state into a shared mixin and reuses SeekIndicator for YouTube-style double-tap seeking on mobile. This PR stays reviewable standalone; #964 rebases once this lands.

[diegotori]

@Ortes please resolve conflicts. Thanks.

[ibrahim-iqbal]

Nice feature — the accumulate-in-same-direction, reset-on-opposite behaviour matches YouTube exactly, and the pill layout at Alignment(±0.6, 0) gives the same off-centre placement.

Widget shape

• SeekIndicator wrapped in IgnorePointer — correct, the pill would otherwise soak up clicks on the middle of the video.
• AnimatedOpacity with a 300 ms fade + a 900 ms hide-timer is the same rhythm as YouTube's own; long enough to read 30 s after a triple-tap, short enough not to overlap a subsequent tap sequence.
• Colors.black.withValues(alpha: 0.55) — good use of the new withValues (the deprecated withOpacity would also work but the current API is right).

Controls plumbing

• _seekIndicatorTimer is cancelled in dispose alongside the existing _hideTimer / _initTimer / _showAfterExpandCollapseTimer — no leak.
• _bumpSeekIndicator gate on chewieController.showSeekIndicator first is right: an embed that disables the feature stays entirely off the setState path, so the widget cost is zero when opted out.
• keyboardSeekDuration is threaded into both directions (the hardcoded Duration(seconds: -10) / Duration(seconds: 10) becomes user-configurable) — nice bonus, plays well with ChewieController.copyWith for downstream users.

Small notes, non-blocking:

• _seekIndicatorSeconds is an int while keyboardSeekDuration is a Duration. If someone sets keyboardSeekDuration: const Duration(milliseconds: 5500), step becomes 5 (via .inSeconds) and the label reads 5 s / 10 s / …, quietly under-counting. Documenting keyboardSeekDuration as "whole seconds" on the field, or clamping the display to duration.inMilliseconds ~/ 1000 explicitly, would make that surprise less likely.
• The Text('$seconds s') label reads correctly in English but ignores locale (Arabic-Indic digits, RTL س, etc.). Fine as-is — chewie doesn't currently localise button/hover strings — but worth a comment if you want to leave a hook for future i18n.
• Two Alignment(±0.6, 0) magic values — arguably nicer as _kIndicatorAlignmentForward / _Backward constants at the top of the file so a designer tweak lands in one place. Nit.

Test file (seek_indicator_test.dart, 133 lines) covers the accumulate/reset behaviour end-to-end, which is exactly what a future refactor of the timer logic will need to preserve. LGTM.

[diegotori]

LGTM.