Dreamio turn documentation · May 26, 2026

Fix VLC Range Cache for MKV Streams

Removed the blanket Matroska/WebM cache bypass so direct-file MKV streams can use Dreamio's local range cache when the origin server confirms byte-range support.

Summary

Dreamio was refusing to range-cache MKV streams before checking the server. That made Torrentio and Real-Debrid MKV playback open in direct mode, so seek prefetch could not run. The cache probe now lets normal HTTP range capability decide whether the local cache should be used.

Changes Made

Removed the hard-coded cache bypass for .mkv, .mk3d, .mka, .mks, and .webm URLs.
Kept the existing non-HTTP and HLS playlist fallbacks intact.
Updated the range probe regression test so MKV URLs are cacheable when the server returns Accept-Ranges: bytes and a valid Content-Length.

Context

The diagnostic logs showed [DreamioVLC] cache fallback reason=tail-index-container, followed by opening mode=direct and direct-mode seek logs. That fallback came from an extension check, not a failed HTTP range probe. Because many debrid MKV streams do support byte ranges, the app was leaving useful buffering behavior on the table.

Important Implementation Details

The probe still requires either a HEAD response with byte-range support and content length, or a successful GET Range: bytes=0-0 response.
If an MKV origin ignores range requests, Dreamio still falls back to direct playback through the existing range-probe-status-... path.
The expected debug signal for a compatible MKV is now [DreamioVLC] opening mode=local-cache, and seeks should include byteOffset=....

Relevant Diff Snippets

Dreamio/ProgressiveHTTPRangeCache.swift

-8

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        guard !url.path.lowercased().hasSuffix(".m3u8") else {
            return HTTPRangeProbeResult(isCacheable: false, contentLength: nil, fallbackReason: "hls-playlist")
        }
        guard !Self.shouldBypassCache(for: url) else {
            return HTTPRangeProbeResult(isCacheable: false, contentLength: nil, fallbackReason: "tail-index-container")
        }

        if let head = try? await response(for: request(method: "HEAD")),
           (200..<400).contains(head.statusCode) {
            let acceptsRanges = header("Accept-Ranges", in: head)?.lowercased().contains("bytes") == true
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        response.value(forHTTPHeaderField: name)
    }

    private static func shouldBypassCache(for url: URL) -> Bool {
        let extensionName = url.pathExtension.lowercased()
        return ["mkv", "mk3d", "mka", "mks", "webm"].contains(extensionName)
    }
}

enum HTTPRangeCacheError: Error {271 unmodified lines
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        guard !url.path.lowercased().hasSuffix(".m3u8") else {
            return HTTPRangeProbeResult(isCacheable: false, contentLength: nil, fallbackReason: "hls-playlist")
        }
        if let head = try? await response(for: request(method: "HEAD")),
           (200..<400).contains(head.statusCode) {
            let acceptsRanges = header("Accept-Ranges", in: head)?.lowercased().contains("bytes") == true
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        response.value(forHTTPHeaderField: name)
    }

}

enum HTTPRangeCacheError: Error {

Tests/StreamResolverTests.swift

-8+13

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        testRangeCacheForegroundMissFetchesAlignedChunks()
        await testRangeCacheForegroundMissReprioritizesPrefetch()
        await testRangeCacheHitFollowsActualPostSeekReadArea()
        await testRangeProbeBypassesTailIndexContainers()
        await testRangeProbeFallsBackWhenServerIgnoresRange()
        await testRangeFetcherPreservesHeaders()
        print("StreamResolverTests passed")
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        try? await Task.sleep(nanoseconds: 50_000_000)
    }

    private static func testRangeProbeBypassesTailIndexContainers() async {
        var requestCount = 0
        MockURLProtocol.handler = { request in
            requestCount += 1
            let response = HTTPURLResponse(
                url: request.url!,
                statusCode: 206,
                httpVersion: nil,
                headerFields: ["Content-Range": "bytes 0-0/20"]
            )!
            return (Data([1]), response)
        }

        let fetcher = HTTPRangeRemoteFetcher(
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        )
        let probe = await fetcher.probe()

        assertEqual(probe.isCacheable, false)
        assertEqual(probe.fallbackReason, "tail-index-container")
        assertEqual(requestCount, 0)
        MockURLProtocol.handler = nil
    }

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        testRangeCacheForegroundMissFetchesAlignedChunks()
        await testRangeCacheForegroundMissReprioritizesPrefetch()
        await testRangeCacheHitFollowsActualPostSeekReadArea()
        await testRangeProbeAllowsRangeCacheForMKVWhenServerSupportsRanges()
        await testRangeProbeFallsBackWhenServerIgnoresRange()
        await testRangeFetcherPreservesHeaders()
        print("StreamResolverTests passed")
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        try? await Task.sleep(nanoseconds: 50_000_000)
    }

    private static func testRangeProbeAllowsRangeCacheForMKVWhenServerSupportsRanges() async {
        var requestCount = 0
        MockURLProtocol.handler = { request in
            requestCount += 1
            assertEqual(request.httpMethod, "HEAD")
            let response = HTTPURLResponse(
                url: request.url!,
                statusCode: 200,
                httpVersion: nil,
                headerFields: [
                    "Accept-Ranges": "bytes",
                    "Content-Length": "20"
                ]
            )!
            return (Data(), response)
        }

        let fetcher = HTTPRangeRemoteFetcher(
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        )
        let probe = await fetcher.probe()

        assertEqual(probe.isCacheable, true)
        assertEqual(probe.contentLength, 20)
        assertEqual(probe.fallbackReason, nil)
        assertEqual(requestCount, 1)
        MockURLProtocol.handler = nil
    }

Expected Impact for End-Users

Compatible MKV direct-file streams should start through Dreamio's local range cache instead of direct VLC mode. Backward and forward skips can now prime nearby bytes, which should reduce stalls after seeking on supported servers.

Validation

Passed swiftc Dreamio/StreamCandidate.swift Dreamio/StreamResolver.swift Dreamio/ProgressiveHTTPRangeCache.swift Dreamio/ExternalSubtitleTrackParser.swift Tests/StreamResolverTests.swift -o /tmp/StreamResolverTests && /tmp/StreamResolverTests
Passed DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer xcodebuild -workspace Dreamio.xcworkspace -scheme Dreamio -configuration Debug -sdk iphonesimulator build

Issues, Limitations, and Mitigations

This does not guarantee every MKV will use the cache. Servers that lack byte-range support, omit content length, reject range requests, or fail the local cache server setup still fall back to direct VLC playback. That is intentional so playback continues instead of failing hard.

Follow-up Work

Test the original Torrentio/Real-Debrid South Park stream on device and confirm logs show opening mode=local-cache.
If startup is slower on some MKV sources, consider measuring HEAD latency and falling back to the tiny range probe sooner.
Improve external subtitle auto-selection so English does not lose to the first parsed subtitle track.

New Changes as of May 26, 2026 at 8:16 AM

Summary of changes

Added a short timeout to the range-cache probe path so a slow HEAD or tiny range request cannot prevent native playback from starting.

Why this change was made

Device logs showed the MKV stream reached [DreamioVLC] cache-probe but never logged either opening mode=local-cache or opening mode=direct before the native-player startup timeout. The cache probe was waiting too long before any VLC media was opened.

Code diffs

Dreamio/ProgressiveHTTPRangeCache.swift

-4+7

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        self.session = session
    }

    func probe() async -> HTTPRangeProbeResult {
        guard ["http", "https"].contains(url.scheme?.lowercased() ?? "") else {
            return HTTPRangeProbeResult(isCacheable: false, contentLength: nil, fallbackReason: "non-http-url")
        }
        guard !url.path.lowercased().hasSuffix(".m3u8") else {
            return HTTPRangeProbeResult(isCacheable: false, contentLength: nil, fallbackReason: "hls-playlist")
        }
        if let head = try? await response(for: request(method: "HEAD")),
           (200..<400).contains(head.statusCode) {
            let acceptsRanges = header("Accept-Ranges", in: head)?.lowercased().contains("bytes") == true
            let length = header("Content-Length", in: head).flatMap(Int64.init)
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            }
        }

        var tinyRequest = request(method: "GET")
        tinyRequest.setValue("bytes=0-0", forHTTPHeaderField: "Range")
        do {
            let (data, response) = try await session.data(for: tinyRequest)
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        return response as? HTTPURLResponse
    }

    private func request(method: String) -> URLRequest {
        var request = URLRequest(url: url)
        request.httpMethod = method
        headers.forEach { key, value in
            request.setValue(value, forHTTPHeaderField: key)
        }264 unmodified lines
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        self.session = session
    }

    func probe(timeoutInterval: TimeInterval = 3) async -> HTTPRangeProbeResult {
        guard ["http", "https"].contains(url.scheme?.lowercased() ?? "") else {
            return HTTPRangeProbeResult(isCacheable: false, contentLength: nil, fallbackReason: "non-http-url")
        }
        guard !url.path.lowercased().hasSuffix(".m3u8") else {
            return HTTPRangeProbeResult(isCacheable: false, contentLength: nil, fallbackReason: "hls-playlist")
        }
        if let head = try? await response(for: request(method: "HEAD", timeoutInterval: timeoutInterval)),
           (200..<400).contains(head.statusCode) {
            let acceptsRanges = header("Accept-Ranges", in: head)?.lowercased().contains("bytes") == true
            let length = header("Content-Length", in: head).flatMap(Int64.init)
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            }
        }

        var tinyRequest = request(method: "GET", timeoutInterval: timeoutInterval)
        tinyRequest.setValue("bytes=0-0", forHTTPHeaderField: "Range")
        do {
            let (data, response) = try await session.data(for: tinyRequest)
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        return response as? HTTPURLResponse
    }

    private func request(method: String, timeoutInterval: TimeInterval? = nil) -> URLRequest {
        var request = URLRequest(url: url)
        request.httpMethod = method
        if let timeoutInterval {
            request.timeoutInterval = timeoutInterval
        }
        headers.forEach { key, value in
            request.setValue(value, forHTTPHeaderField: key)
        }

Dreamio/VLCNativePlaybackBackend.swift

-1+1

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                return
            }
            let fetcher = HTTPRangeRemoteFetcher(url: request.playbackURL, headers: request.headers)
            let probe = await fetcher.probe()
            guard !Task.isCancelled else {
                return
            }77 unmodified lines
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                return
            }
            let fetcher = HTTPRangeRemoteFetcher(url: request.playbackURL, headers: request.headers)
            let probe = await fetcher.probe(timeoutInterval: 1.5)
            guard !Task.isCancelled else {
                return
            }

Tests/StreamResolverTests.swift

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        await testRangeCacheForegroundMissReprioritizesPrefetch()
        await testRangeCacheHitFollowsActualPostSeekReadArea()
        await testRangeProbeAllowsRangeCacheForMKVWhenServerSupportsRanges()
        await testRangeProbeFallsBackWhenServerIgnoresRange()
        await testRangeFetcherPreservesHeaders()
        print("StreamResolverTests passed")
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        MockURLProtocol.handler = nil
    }

    private static func byteRange(fromHeader header: String, contentLength: Int64) -> HTTPByteRange {
        let value = header.replacingOccurrences(of: "bytes=", with: "")
        let pieces = value.split(separator: "-", maxSplits: 1).map(String.init)43 unmodified lines
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        await testRangeCacheForegroundMissReprioritizesPrefetch()
        await testRangeCacheHitFollowsActualPostSeekReadArea()
        await testRangeProbeAllowsRangeCacheForMKVWhenServerSupportsRanges()
        await testRangeProbeAppliesRequestTimeout()
        await testRangeProbeFallsBackWhenServerIgnoresRange()
        await testRangeFetcherPreservesHeaders()
        print("StreamResolverTests passed")
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        MockURLProtocol.handler = nil
    }

    private static func testRangeProbeAppliesRequestTimeout() async {
        MockURLProtocol.handler = { request in
            assertEqual(request.timeoutInterval, 1.5)
            let response = HTTPURLResponse(
                url: request.url!,
                statusCode: 200,
                httpVersion: nil,
                headerFields: [
                    "Accept-Ranges": "bytes",
                    "Content-Length": "20"
                ]
            )!
            return (Data(), response)
        }

        let fetcher = HTTPRangeRemoteFetcher(
            url: URL(string: "https://cdn.example.test/show.mkv")!,
            headers: [:],
            session: mockSession()
        )
        let probe = await fetcher.probe(timeoutInterval: 1.5)

        assertEqual(probe.isCacheable, true)
        MockURLProtocol.handler = nil
    }

    private static func byteRange(fromHeader header: String, contentLength: Int64) -> HTTPByteRange {
        let value = header.replacingOccurrences(of: "bytes=", with: "")
        let pieces = value.split(separator: "-", maxSplits: 1).map(String.init)

Related issues or PRs

Beads issue: dreamio-btc. This follows the earlier dreamio-3sw MKV cache enablement work.

Validation

Passed swiftc Dreamio/StreamCandidate.swift Dreamio/StreamResolver.swift Dreamio/ProgressiveHTTPRangeCache.swift Dreamio/ExternalSubtitleTrackParser.swift Tests/StreamResolverTests.swift -o /tmp/StreamResolverTests && /tmp/StreamResolverTests
Passed DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer xcodebuild -workspace Dreamio.xcworkspace -scheme Dreamio -configuration Debug -sdk iphonesimulator build

New Changes as of May 26, 2026 at 9:01 AM

Summary of changes

Changed VLC startup to open direct playback immediately instead of waiting for the range-cache probe.

Why this change was made

Device logs showed the probe request timing out and the native player still failing to start before the startup watchdog. The reliable behavior is to start VLC first, then revisit cache probing as a non-blocking optimization later.

Code diffs

Dreamio/VLCNativePlaybackBackend.swift

-53+9

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        lastLoggedState = nil
        lastBufferingLogTime = nil
#if DEBUG
        print("[DreamioVLC] cache-probe url=\(URLRedactor.redactedURLString(request.playbackURL.absoluteString))")
#endif
        playbackStartupTask = Task { [weak self] in
            guard let self else {
                return
            }
            let fetcher = HTTPRangeRemoteFetcher(url: request.playbackURL, headers: request.headers)
            let probe = await fetcher.probe(timeoutInterval: 1.5)
            guard !Task.isCancelled else {
                return
            }

            if probe.isCacheable, let contentLength = probe.contentLength, contentLength > 0 {
                do {
                    let session = ProgressiveHTTPRangeCacheSession(
                        fetcher: fetcher,
                        contentLength: contentLength,
                        durationProvider: { [weak self] in self?.duration ?? 0 }
                    )
                    let localURL = try await ProgressiveHTTPRangeCacheServer.shared.localURL(for: session)
                    await MainActor.run {
                        self.rangeCacheSession = session
                        session.prefetch(aroundByteOffset: 0)
                        self.startVLCMedia(
                            url: localURL,
                            request: request,
                            playbackMode: "local-cache",
                            cachingMilliseconds: 500,
                            includeRemoteHTTPOptions: false
                        )
                    }
                    return
                } catch {
#if DEBUG
                    print("[DreamioVLC] cache fallback reason=local-server-error-\(error)")
#endif
                }
            } else {
#if DEBUG
                print("[DreamioVLC] cache fallback reason=\(probe.fallbackReason ?? "unknown")")
#endif
            }

            await MainActor.run {
                self.startVLCMedia(
                    url: request.playbackURL,
                    request: request,
                    playbackMode: "direct",
                    cachingMilliseconds: 2500,
                    includeRemoteHTTPOptions: true
                )
            }
        }
#else
        onFailure?(NativePlaybackError.backendUnavailable)
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        lastLoggedState = nil
        lastBufferingLogTime = nil
#if DEBUG
        print("[DreamioVLC] cache fallback reason=startup-direct-preferred url=\(URLRedactor.redactedURLString(request.playbackURL.absoluteString))")
#endif
        startVLCMedia(
            url: request.playbackURL,
            request: request,
            playbackMode: "direct",
            cachingMilliseconds: 2500,
            includeRemoteHTTPOptions: true
        )
#else
        onFailure?(NativePlaybackError.backendUnavailable)
#endif

Related issues or PRs

Beads issue: dreamio-dd7. This supersedes the blocking startup probe behavior from the earlier MKV range-cache experiment.

Validation

Passed swiftc Dreamio/StreamCandidate.swift Dreamio/StreamResolver.swift Dreamio/ProgressiveHTTPRangeCache.swift Dreamio/ExternalSubtitleTrackParser.swift Tests/StreamResolverTests.swift -o /tmp/StreamResolverTests && /tmp/StreamResolverTests
Passed DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer xcodebuild -workspace Dreamio.xcworkspace -scheme Dreamio -configuration Debug -sdk iphonesimulator build