Dreamio turn record

Queue VLC Subtitles Until Media Start

Fixed a startup race introduced by the real local range buffer: subtitle candidates can now arrive during the cache probe and wait safely until VLC has an active media item.

Issue dreamio-qyh May 25, 2026 Native playback

Summary

The native VLC backend now queues external subtitle candidates received before media startup completes. Once the local-cache or direct VLC media item is created and playback begins, the queued candidates are flushed through the existing subtitle attachment path.

Changes Made

Added a pending subtitle queue and URL set to VLCNativePlaybackBackend.
Reset the queue and startup flag for each new playback request.
Marked media as started inside startVLCMedia, then flushed queued subtitles.
Kept the existing attachment, dedupe, delayed refresh, display-name preservation, and auto-selection behavior intact.

Context

The logs showed subtitle attachments happening after cache-probe but before opening mode=local-cache. With the real range cache, VLC media creation is delayed by the async probe and local server setup. The native player still forwarded buffered subtitles immediately, so addPlaybackSlave was called while VLC had no active media item.

Important Implementation Details

The fix treats pre-media subtitle candidates as valid work, not duplicates. Candidates queued during startup are not inserted into attachedSubtitleURLs; they are held separately so the later flush can attach them normally once VLC is ready.

When subtitles arrive after media startup, behavior is unchanged. They still attach immediately and use the existing delayed refresh timers to wait for VLC to expose external subtitle tracks.

Relevant Diff Snippets

Rendered with @pierre/diffs/ssr from the one-file patch for Dreamio/VLCNativePlaybackBackend.swift.

Dreamio/VLCNativePlaybackBackend.swift

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    private var lastLoggedState: String?
    private var lastBufferingLogTime: Date?
    private var attachedSubtitleURLs = Set<URL>()
    private var didAutoSelectSubtitleTrack = false
    private var didUserSelectSubtitleTrack = false
    private var autoSelectedSubtitleTrackID: Int32?
20 unmodified lines
#if canImport(MobileVLCKit)
        playbackStartupTask?.cancel()
        attachedSubtitleURLs.removeAll()
        didAutoSelectSubtitleTrack = false
        didUserSelectSubtitleTrack = false
        autoSelectedSubtitleTrackID = nil
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        print("[DreamioVLC] opening mode=\(playbackMode) cachingMs=\(cachingMilliseconds) url=\(URLRedactor.redactedURLString(url.absoluteString))")
#endif
        mediaPlayer.play()
    }

    private func addRemoteHeaders(to media: VLCMedia, request: NativePlaybackRequest) {
10 unmodified lines
    }

    private func attachSubtitles(_ candidates: [SubtitleCandidate]) -> Int {
        var attachedCount = 0
        var duplicateCount = 0
        let baselineTrackIDs = Set(rawSubtitleTracks().filter { $0.id >= 0 }.map(\.id))
36 unmodified lines
        return attachedCount
    }

    private func rawSubtitleTracks() -> [SubtitleTrack] {
        let names = mediaPlayer.videoSubTitlesNames as? [String] ?? []
        let indexes = mediaPlayer.videoSubTitlesIndexes as? [NSNumber] ?? []27 unmodified lines
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    private var lastLoggedState: String?
    private var lastBufferingLogTime: Date?
    private var attachedSubtitleURLs = Set<URL>()
    private var pendingSubtitleCandidates: [SubtitleCandidate] = []
    private var pendingSubtitleURLs = Set<URL>()
    private var hasStartedMedia = false
    private var didAutoSelectSubtitleTrack = false
    private var didUserSelectSubtitleTrack = false
    private var autoSelectedSubtitleTrackID: Int32?
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#if canImport(MobileVLCKit)
        playbackStartupTask?.cancel()
        attachedSubtitleURLs.removeAll()
        pendingSubtitleCandidates.removeAll()
        pendingSubtitleURLs.removeAll()
        hasStartedMedia = false
        didAutoSelectSubtitleTrack = false
        didUserSelectSubtitleTrack = false
        autoSelectedSubtitleTrackID = nil
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        print("[DreamioVLC] opening mode=\(playbackMode) cachingMs=\(cachingMilliseconds) url=\(URLRedactor.redactedURLString(url.absoluteString))")
#endif
        mediaPlayer.play()
        hasStartedMedia = true
        flushPendingSubtitleCandidates()
    }

    private func addRemoteHeaders(to media: VLCMedia, request: NativePlaybackRequest) {
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    }

    private func attachSubtitles(_ candidates: [SubtitleCandidate]) -> Int {
        guard hasStartedMedia else {
            let queued = queuePendingSubtitleCandidates(candidates)
#if DEBUG
            if !candidates.isEmpty {
                print("[DreamioVLC] subtitle candidates=\(candidates.count) queued=\(queued) reason=media-not-started")
            }
#endif
            return queued
        }

        var attachedCount = 0
        var duplicateCount = 0
        let baselineTrackIDs = Set(rawSubtitleTracks().filter { $0.id >= 0 }.map(\.id))
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        return attachedCount
    }

    private func queuePendingSubtitleCandidates(_ candidates: [SubtitleCandidate]) -> Int {
        var queuedCount = 0
        candidates.forEach { candidate in
            guard !attachedSubtitleURLs.contains(candidate.url),
                  !pendingSubtitleURLs.contains(candidate.url)
            else {
                return
            }

            pendingSubtitleURLs.insert(candidate.url)
            pendingSubtitleCandidates.append(candidate)
            queuedCount += 1
        }
        return queuedCount
    }

    private func flushPendingSubtitleCandidates() {
        guard !pendingSubtitleCandidates.isEmpty else {
            return
        }

        let candidates = pendingSubtitleCandidates
        pendingSubtitleCandidates.removeAll()
        pendingSubtitleURLs.removeAll()
#if DEBUG
        print("[DreamioVLC] flushing queued subtitles count=\(candidates.count)")
#endif
        _ = attachSubtitles(candidates)
    }

    private func rawSubtitleTracks() -> [SubtitleTrack] {
        let names = mediaPlayer.videoSubTitlesNames as? [String] ?? []
        let indexes = mediaPlayer.videoSubTitlesIndexes as? [NSNumber] ?? []

New Changes as of May 25, 2026 at 6:55 PM EDT

Summary of changes

After the queue fix landed, device logs showed the queued subtitles flushing after VLC media startup, but VLC still exposed no subtitle tracks. The remaining problem was the subtitle URL shape: Stremio provider download URLs are extensionless and VLC accepts them without creating visible external subtitle tracks.

The subtitle resolver now downloads resolvable subtitle bodies and caches them as local files with real subtitle extensions before handing them to VLC. Stremio download URLs are still parsed as candidates, but they are no longer treated as direct VLC-ready subtitle files.

Why this change was made

The native backend debug output showed ext=none for every attached Stremio subtitle and visible=0 after attachment. Caching the subtitle payload gives VLC a local .srt, .vtt, or .ass file, which is a more reliable attachment target than a provider download endpoint.

Code diffs

Dreamio/StreamResolver.swift

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final class SubtitleResolver: SubtitleResolving {
    private let session: URLSession

    init(session: URLSession = .shared) {
        self.session = session
    }

    func resolve(_ candidate: SubtitleCandidate) async -> SubtitleCandidate? {
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                return SubtitleCandidate(url: finalURL, label: candidate.label, language: candidate.language)
            }

            return Self.bestPlayableCandidate(
                from: data,
                responseURL: response.url,
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        }
    }

    static func bestPlayableCandidate(
        from data: Data,
        responseURL: URL?,
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        let lowercased = url.absoluteString.lowercased()
        return ["srt", "vtt", "ass", "ssa", "sub"].contains(url.pathExtension.lowercased())
            || [".srt?", ".vtt?", ".ass?", ".ssa?", ".sub?", ".srt&", ".vtt&", ".ass&", ".ssa&", ".sub&"].contains(where: lowercased.contains)
            || isStremioSubtitleDownloadURL(url)
    }

    private static func shouldResolve(_ url: URL) -> Bool {
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            || path.range(of: #"(^|/)download(/|$)"#, options: .regularExpression) != nil
    }

    private static func logRejected(_ candidate: SubtitleCandidate, responseURL: URL?, data: Data) -> SubtitleCandidate? {
#if DEBUG
        let responseDescription = responseURL.map { URLRedactor.redactedURLString($0.absoluteString) } ?? "none"34 unmodified lines
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final class SubtitleResolver: SubtitleResolving {
    private let session: URLSession
    private let cacheDirectory: URL

    init(
        session: URLSession = .shared,
        cacheDirectory: URL = FileManager.default.temporaryDirectory.appendingPathComponent("DreamioSubtitles", isDirectory: true)
    ) {
        self.session = session
        self.cacheDirectory = cacheDirectory
    }

    func resolve(_ candidate: SubtitleCandidate) async -> SubtitleCandidate? {
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                return SubtitleCandidate(url: finalURL, label: candidate.label, language: candidate.language)
            }

            if let cachedCandidate = cacheSubtitleDataIfNeeded(data, original: candidate) {
                return cachedCandidate
            }

            return Self.bestPlayableCandidate(
                from: data,
                responseURL: response.url,
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        }
    }

    private func cacheSubtitleDataIfNeeded(_ data: Data, original: SubtitleCandidate) -> SubtitleCandidate? {
        guard let subtitleType = Self.subtitleType(in: data) else {
            return nil
        }

        do {
            try FileManager.default.createDirectory(
                at: cacheDirectory,
                withIntermediateDirectories: true
            )
            let filename = "\(UUID().uuidString).\(subtitleType.fileExtension)"
            let fileURL = cacheDirectory.appendingPathComponent(filename)
            try data.write(to: fileURL, options: .atomic)
#if DEBUG
            print("[DreamioSubtitles] cached subtitle url=\(URLRedactor.redactedURLString(original.url.absoluteString)) file=\(fileURL.lastPathComponent)")
#endif
            return SubtitleCandidate(url: fileURL, label: original.label, language: original.language)
        } catch {
#if DEBUG
            print("[DreamioSubtitles] cache failure=\(error.localizedDescription) url=\(URLRedactor.redactedURLString(original.url.absoluteString))")
#endif
            return nil
        }
    }

    static func bestPlayableCandidate(
        from data: Data,
        responseURL: URL?,
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        let lowercased = url.absoluteString.lowercased()
        return ["srt", "vtt", "ass", "ssa", "sub"].contains(url.pathExtension.lowercased())
            || [".srt?", ".vtt?", ".ass?", ".ssa?", ".sub?", ".srt&", ".vtt&", ".ass&", ".ssa&", ".sub&"].contains(where: lowercased.contains)
    }

    private static func shouldResolve(_ url: URL) -> Bool {
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            || path.range(of: #"(^|/)download(/|$)"#, options: .regularExpression) != nil
    }

    private enum SubtitlePayloadType {
        case srt
        case vtt
        case ass

        var fileExtension: String {
            switch self {
            case .srt:
                return "srt"
            case .vtt:
                return "vtt"
            case .ass:
                return "ass"
            }
        }
    }

    private static func subtitleType(in data: Data) -> SubtitlePayloadType? {
        guard !data.isEmpty,
              let text = String(data: data.prefix(4096), encoding: .utf8)?
                .trimmingCharacters(in: .whitespacesAndNewlines),
              !text.isEmpty
        else {
            return nil
        }

        let lowercased = text.lowercased()
        if lowercased.hasPrefix("webvtt") {
            return .vtt
        }
        if lowercased.hasPrefix("[script info]")
            || lowercased.contains("\n[events]")
            || lowercased.contains("\r\n[events]") {
            return .ass
        }
        if lowercased.range(
            of: #"(?m)^\d+\s*[\r\n]+(?:\d{1,2}:)?\d{2}:\d{2}[,.]\d{3}\s*-->\s*(?:\d{1,2}:)?\d{2}:\d{2}[,.]\d{3}"#,
            options: .regularExpression
        ) != nil {
            return .srt
        }
        return nil
    }

    private static func logRejected(_ candidate: SubtitleCandidate, responseURL: URL?, data: Data) -> SubtitleCandidate? {
#if DEBUG
        let responseDescription = responseURL.map { URLRedactor.redactedURLString($0.absoluteString) } ?? "none"

Tests/StreamResolverTests.swift

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        testStremioSubtitleDownloadURLParsing()
        testOpenSubtitlesV3DownloadResponseResolution()
        testOpenSubtitlesNestedDownloadResponseResolution()
        await testSubtitleResolverDownloadJSONReturningLink()
        await testSubtitleResolverRedirectToDirectSubtitle()
        await testSubtitleResolverRejectsNonSubtitleAPIResponse()
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        assertEqual(candidates[0].url.absoluteString, "https://subs5.strem.io/en/download/subencoding-stremio-utf8/src-api/file/1952341941")
        assertEqual(candidates[0].label, "English")
        assertEqual(candidates[0].language, "eng")
        assert(SubtitleResolver.isDirectSubtitleFile(candidates[0].url), "Expected Stremio subtitle downloads to be attachable without another resolver hop")
    }

    private static func testContentRangeParsing() {
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        assertEqual(candidate?.language, "eng")
    }

    private static func testSubtitleResolverDownloadJSONReturningLink() async {
        MockURLProtocol.handlers = [
            "https://api.opensubtitles.com/api/v1/download/123": (
                200,
14 unmodified lines
    }

    private static func testSubtitleResolverRedirectToDirectSubtitle() async {
        MockURLProtocol.handlers = [
            "https://api.opensubtitles.com/api/v1/download/redirect": (
                200,
12 unmodified lines
    }

    private static func testSubtitleResolverRejectsNonSubtitleAPIResponse() async {
        MockURLProtocol.handlers = [
            "https://api.opensubtitles.com/api/v1/download/not-found": (
                200,15 unmodified lines
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        testStremioSubtitleDownloadURLParsing()
        testOpenSubtitlesV3DownloadResponseResolution()
        testOpenSubtitlesNestedDownloadResponseResolution()
        await testSubtitleResolverCachesStremioDownloadBody()
        await testSubtitleResolverDownloadJSONReturningLink()
        await testSubtitleResolverRedirectToDirectSubtitle()
        await testSubtitleResolverRejectsNonSubtitleAPIResponse()
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        assertEqual(candidates[0].url.absoluteString, "https://subs5.strem.io/en/download/subencoding-stremio-utf8/src-api/file/1952341941")
        assertEqual(candidates[0].label, "English")
        assertEqual(candidates[0].language, "eng")
        assert(!SubtitleResolver.isDirectSubtitleFile(candidates[0].url), "Expected Stremio subtitle downloads to be resolved before VLC attachment")
    }

    private static func testContentRangeParsing() {
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        assertEqual(candidate?.language, "eng")
    }

    private static func testSubtitleResolverCachesStremioDownloadBody() async {
        let sourceURL = "https://subs5.strem.io/en/download/subencoding-stremio-utf8/src-api/file/1952341941"
        let subtitleBody = """
        1
        00:00:01,000 --> 00:00:02,000
        Hello from Stremio

        """
        MockURLProtocol.handler = nil
        MockURLProtocol.handlers = [
            sourceURL: (
                200,
                URL(string: sourceURL)!,
                subtitleBody.data(using: .utf8)!
            )
        ]

        let cacheDirectory = FileManager.default.temporaryDirectory
            .appendingPathComponent("DreamioSubtitleResolverTests-\(UUID().uuidString)", isDirectory: true)
        defer {
            try? FileManager.default.removeItem(at: cacheDirectory)
        }

        let resolver = SubtitleResolver(session: mockSession(), cacheDirectory: cacheDirectory)
        let candidate = await resolver.resolve(SubtitleCandidate(
            url: URL(string: sourceURL)!,
            label: "English",
            language: "eng"
        ))

        assertEqual(candidate?.url.isFileURL, true)
        assertEqual(candidate?.url.pathExtension, "srt")
        assertEqual(candidate?.label, "English")
        assertEqual(candidate?.language, "eng")
        let cachedBody = try? String(contentsOf: candidate!.url, encoding: .utf8)
        assertEqual(cachedBody, subtitleBody)
    }

    private static func testSubtitleResolverDownloadJSONReturningLink() async {
        MockURLProtocol.handler = nil
        MockURLProtocol.handlers = [
            "https://api.opensubtitles.com/api/v1/download/123": (
                200,
14 unmodified lines
    }

    private static func testSubtitleResolverRedirectToDirectSubtitle() async {
        MockURLProtocol.handler = nil
        MockURLProtocol.handlers = [
            "https://api.opensubtitles.com/api/v1/download/redirect": (
                200,
12 unmodified lines
    }

    private static func testSubtitleResolverRejectsNonSubtitleAPIResponse() async {
        MockURLProtocol.handler = nil
        MockURLProtocol.handlers = [
            "https://api.opensubtitles.com/api/v1/download/not-found": (
                200,

Related issues or PRs

Related Beads issue: dreamio-771.

New Changes as of May 25, 2026 at 7:00 PM EDT

Summary of changes

Device logs showed Stremio subtitle downloads returning text, but the strict resolver detector rejected every body as text-without-direct-subtitle. The resolver now accepts plausible plain subtitle text from Stremio download endpoints and caches it as a local .srt file.

Why this change was made

The previous cache step only recognized classic indexed SRT, WebVTT, and ASS signatures. The live Stremio payloads appear to be subtitle-like text without matching that narrow signature, so they never reached VLC. This update keeps strict handling for general URLs while applying a provider-specific fallback for Stremio subtitle downloads.

Code diffs

Dreamio/StreamResolver.swift

-3+37

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    }

    private func cacheSubtitleDataIfNeeded(_ data: Data, original: SubtitleCandidate) -> SubtitleCandidate? {
        guard let subtitleType = Self.subtitleType(in: data) else {
            return nil
        }

100 unmodified lines
        }
    }

    private static func subtitleType(in data: Data) -> SubtitlePayloadType? {
        guard !data.isEmpty,
              let text = String(data: data.prefix(4096), encoding: .utf8)?
                .trimmingCharacters(in: .whitespacesAndNewlines),
17 unmodified lines
        ) != nil {
            return .srt
        }
        return nil
    }

    private static func logRejected(_ candidate: SubtitleCandidate, responseURL: URL?, data: Data) -> SubtitleCandidate? {
#if DEBUG
        let responseDescription = responseURL.map { URLRedactor.redactedURLString($0.absoluteString) } ?? "none"
7 unmodified lines
        } else {
            bodyKind = "unreadable"
        }
        print("[DreamioSubtitles] rejected candidate reason=\(bodyKind) url=\(URLRedactor.redactedURLString(candidate.url.absoluteString)) responseURL=\(responseDescription)")
#endif
        return nil
    }
}

protocol StreamResolving {96 unmodified lines
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    }

    private func cacheSubtitleDataIfNeeded(_ data: Data, original: SubtitleCandidate) -> SubtitleCandidate? {
        guard let subtitleType = Self.subtitleType(in: data, sourceURL: original.url) else {
            return nil
        }

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        }
    }

    private static func subtitleType(in data: Data, sourceURL: URL? = nil) -> SubtitlePayloadType? {
        guard !data.isEmpty,
              let text = String(data: data.prefix(4096), encoding: .utf8)?
                .trimmingCharacters(in: .whitespacesAndNewlines),
17 unmodified lines
        ) != nil {
            return .srt
        }
        if let sourceURL,
           isStremioSubtitleDownloadURL(sourceURL),
           isPlausiblePlainSubtitleText(text) {
            return .srt
        }
        return nil
    }

    private static func isPlausiblePlainSubtitleText(_ text: String) -> Bool {
        let lowercased = text.lowercased()
        guard !lowercased.hasPrefix("{"),
              !lowercased.hasPrefix("["),
              !lowercased.hasPrefix("<!doctype"),
              !lowercased.hasPrefix("<html"),
              !lowercased.hasPrefix("<?xml")
        else {
            return false
        }

        return lowercased.contains("-->")
            || lowercased.contains("<font")
            || lowercased.contains("{\\")
            || lowercased.contains("\\n")
            || lowercased.split(whereSeparator: \.isNewline).count > 1
    }

    private static func logRejected(_ candidate: SubtitleCandidate, responseURL: URL?, data: Data) -> SubtitleCandidate? {
#if DEBUG
        let responseDescription = responseURL.map { URLRedactor.redactedURLString($0.absoluteString) } ?? "none"
7 unmodified lines
        } else {
            bodyKind = "unreadable"
        }
        print("[DreamioSubtitles] rejected candidate reason=\(bodyKind) url=\(URLRedactor.redactedURLString(candidate.url.absoluteString)) responseURL=\(responseDescription) preview=\(rejectionPreview(data))")
#endif
        return nil
    }

#if DEBUG
    private static func rejectionPreview(_ data: Data) -> String {
        guard let text = String(data: data.prefix(180), encoding: .utf8) else {
            return "unreadable"
        }
        return text
            .replacingOccurrences(of: "\n", with: "\\n")
            .replacingOccurrences(of: "\r", with: "\\r")
    }
#endif
}

protocol StreamResolving {

Tests/StreamResolverTests.swift

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        testOpenSubtitlesV3DownloadResponseResolution()
        testOpenSubtitlesNestedDownloadResponseResolution()
        await testSubtitleResolverCachesStremioDownloadBody()
        await testSubtitleResolverDownloadJSONReturningLink()
        await testSubtitleResolverRedirectToDirectSubtitle()
        await testSubtitleResolverRejectsNonSubtitleAPIResponse()
453 unmodified lines
        assertEqual(cachedBody, subtitleBody)
    }

    private static func testSubtitleResolverDownloadJSONReturningLink() async {
        MockURLProtocol.handler = nil
        MockURLProtocol.handlers = [16 unmodified lines
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        testOpenSubtitlesV3DownloadResponseResolution()
        testOpenSubtitlesNestedDownloadResponseResolution()
        await testSubtitleResolverCachesStremioDownloadBody()
        await testSubtitleResolverCachesPlainStremioDownloadBody()
        await testSubtitleResolverDownloadJSONReturningLink()
        await testSubtitleResolverRedirectToDirectSubtitle()
        await testSubtitleResolverRejectsNonSubtitleAPIResponse()
453 unmodified lines
        assertEqual(cachedBody, subtitleBody)
    }

    private static func testSubtitleResolverCachesPlainStremioDownloadBody() async {
        let sourceURL = "https://subs5.strem.io/en/download/subencoding-stremio-utf8/src-api/file/1952341942"
        let subtitleBody = """
        00:01.000 --> 00:02.000
        Plain cue text without an index

        """
        MockURLProtocol.handler = nil
        MockURLProtocol.handlers = [
            sourceURL: (
                200,
                URL(string: sourceURL)!,
                subtitleBody.data(using: .utf8)!
            )
        ]

        let cacheDirectory = FileManager.default.temporaryDirectory
            .appendingPathComponent("DreamioSubtitleResolverTests-\(UUID().uuidString)", isDirectory: true)
        defer {
            try? FileManager.default.removeItem(at: cacheDirectory)
        }

        let resolver = SubtitleResolver(session: mockSession(), cacheDirectory: cacheDirectory)
        let candidate = await resolver.resolve(SubtitleCandidate(
            url: URL(string: sourceURL)!,
            label: "English",
            language: "eng"
        ))

        assertEqual(candidate?.url.isFileURL, true)
        assertEqual(candidate?.url.pathExtension, "srt")
        let cachedBody = try? String(contentsOf: candidate!.url, encoding: .utf8)
        assertEqual(cachedBody, subtitleBody)
    }

    private static func testSubtitleResolverDownloadJSONReturningLink() async {
        MockURLProtocol.handler = nil
        MockURLProtocol.handlers = [

Related issues or PRs

Related Beads issue: dreamio-8oe.

Expected Impact for End-Users

When an MKV stream opens through the real local range buffer, subtitles discovered before playback should still appear in the captions menu and be eligible for auto-selection once VLC exposes the track list. Stremio subtitle downloads should now reach VLC as local subtitle files rather than extensionless provider URLs, including plain cue-text payloads that do not match classic indexed SRT.

Validation

Ran git diff --check: passed.
Ran pod install to restore missing local CocoaPods support files in this worktree.
Ran xcodebuild -workspace Dreamio.xcworkspace -scheme Dreamio -destination 'generic/platform=iOS Simulator' -quiet build: passed.
Ran swiftc -parse-as-library -D DEBUG Dreamio/StreamCandidate.swift Dreamio/StreamResolver.swift Dreamio/ProgressiveHTTPRangeCache.swift Tests/StreamResolverTests.swift -o /tmp/StreamResolverTests && /tmp/StreamResolverTests: passed, including the Stremio subtitle cache tests for strict SRT and plain cue text.
The build still reports existing MobileVLCKit warnings about simulator deployment target and a run-script phase, but compilation succeeded.

Issues, Limitations, and Mitigations

This addresses the pre-media attachment race shown in the logs and the follow-on issue where extensionless Stremio subtitle download URLs were accepted by VLC without visible tracks. If a provider returns a compressed archive, a non-UTF-8 payload, HTML/XML, JSON without a direct subtitle link, or a format VLC cannot parse after local caching, that would still need a separate resolver enhancement.

Follow-up Work

Re-test on device with the South Park stream and confirm the log order changes to queued subtitles followed by flushing queued subtitles after opening mode=local-cache.
Re-test on device and look for [DreamioSubtitles] cached subtitle followed by VLC attachment logs with ext=srt, ext=vtt, or ext=ass. If rejection still occurs, inspect the new preview= field in the rejection log.
If tracks still do not appear after local caching, capture whether VLC receives file URLs and whether MobileVLCKit reports any subtitle import errors.