Throttle VLC subtitle reapply

Summary

Dreamio was auto-selecting embedded VLC subtitle tracks correctly, but VLC buffering callbacks repeatedly reapplied the same track while it was already selected. The change keeps recovery behavior for real subtitle-selection drift and startup timing, while suppressing repeated no-op reapply writes from player state changes.

Changes Made

• Added a selected-track guard inside reapplyAutoSelectedSubtitleTrackIfNeeded.
• Kept delayed startup reapply attempts visible by passing shouldLogNoop: true for the 0.3, 1.0, 2.0, and 4.0 second retries.
• Changed debug logging to label reapply events as action=confirm for delayed no-op confirmations or action=recover when VLC had drifted away from the intended subtitle.

Context

The diagnostic log showed VLC auto-selecting English (SDH), then repeatedly logging reapply subtitle during buffering even though selected=3 never changed. The external OpenSubtitles load failure was non-critical in that trace, and the working subtitle came from the MKV itself.

Important Implementation Details

The VLC state delegate still calls the reapply helper during .buffering and .playing. The helper now checks mediaPlayer.currentVideoSubTitleIndex before writing. If the intended auto-selected track is already active, state-driven calls return without touching VLC or logging. Delayed startup retries intentionally keep their confirmation logging because those are bounded and useful for diagnosing timing-sensitive subtitle attachment.

Relevant Diff Snippets

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283 unmodified lines
    private func scheduleAutoSubtitleSelectionReapply(trackID: Int32) {
        [0.3, 1.0, 2.0, 4.0].forEach { delay in
            DispatchQueue.main.asyncAfter(deadline: .now() + delay) { [weak self] in
                self?.reapplyAutoSelectedSubtitleTrackIfNeeded(reason: "delayed-\(String(format: "%.1f", delay))")
            }
        }
    }

    private func reapplyAutoSelectedSubtitleTrackIfNeeded(reason: String) {
        guard !didUserSelectSubtitleTrack,
              let trackID = autoSelectedSubtitleTrackID,
              subtitleTracks.contains(where: { $0.id == trackID }) else {
            return
        }

        mediaPlayer.currentVideoSubTitleIndex = trackID
#if DEBUG
        print("[DreamioVLC] reapply subtitle id=\(trackID) reason=\(reason) selected=\(mediaPlayer.currentVideoSubTitleIndex)")
#endif
    }
#endif
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283 unmodified lines
    private func scheduleAutoSubtitleSelectionReapply(trackID: Int32) {
        [0.3, 1.0, 2.0, 4.0].forEach { delay in
            DispatchQueue.main.asyncAfter(deadline: .now() + delay) { [weak self] in
                self?.reapplyAutoSelectedSubtitleTrackIfNeeded(
                    reason: "delayed-\(String(format: "%.1f", delay))",
                    shouldLogNoop: true
                )
            }
        }
    }

    private func reapplyAutoSelectedSubtitleTrackIfNeeded(reason: String, shouldLogNoop: Bool = false) {
        guard !didUserSelectSubtitleTrack,
              let trackID = autoSelectedSubtitleTrackID,
              subtitleTracks.contains(where: { $0.id == trackID }) else {
            return
        }

        let selectedTrackID = mediaPlayer.currentVideoSubTitleIndex
        guard selectedTrackID != trackID || shouldLogNoop else {
            return
        }

        mediaPlayer.currentVideoSubTitleIndex = trackID
#if DEBUG
        let action = selectedTrackID == trackID ? "confirm" : "recover"
        print("[DreamioVLC] reapply subtitle id=\(trackID) reason=\(reason) action=\(action) selected=\(mediaPlayer.currentVideoSubTitleIndex)")
#endif
    }
#endif

Expected Impact for End-Users

Playback should behave the same when the embedded subtitle is successfully auto-selected. Debug logs should become much quieter during buffering, making real subtitle failures easier to spot. If VLC drops the subtitle selection, Dreamio will still reapply the intended auto-selected track.

Validation

• Ran xcodebuild -workspace Dreamio.xcworkspace -scheme Dreamio -destination 'generic/platform=iOS Simulator' build.
• The build succeeded. Xcode emitted the existing MobileVLCKit run-script output warning and AppIntents metadata skip warning, neither related to this change.

Issues, Limitations, and Mitigations

• This was validated with a simulator build, not a live Stremio playback session against the exact South Park stream from the provided log.
• The OpenSubtitles external subtitle load failure is separate. This change addresses VLC reapply spam after embedded subtitle auto-selection, not remote subtitle download reliability.
• Delayed retry logs remain by design, but they are bounded to four scheduled checks.

Follow-up Work

No follow-up issue is required for this specific buffering log noise. A separate issue would be appropriate if external OpenSubtitles subtitle downloads still fail for streams without embedded subtitles.