Optimize screen sharing latency and frame rate

ios/QueueCube/Backend/API.swift

@@ -62,6 +62,9 @@ struct NowPlayingInfo: Codable
     let playingItem: MediaItem?
     let isPaused: Bool
     let volume: Int
+    let timePosition: Double?
+    let duration: Double?
+    let seekable: Bool?
 }
 
 actor API
@@ -173,6 +176,13 @@ actor API
             .post()
     }
 
+    public func seek(to time: Double) async throws {
+        try await request()
+            .path("/player/seek")
+            .body([ "time" : time ])
+            .post()
+    }
+    
     public func search(query: String) async throws -> FetchResult<[SearchResultItem]> {
         try await request()
             .pathString("/search?q=\(query.uriEncoded())")
@@ -255,10 +265,19 @@ actor API
     
     // MARK: - Types
     
-    enum Error: Swift.Error
+    enum Error: Swift.Error, LocalizedError
     {
         case apiNotConfigured
         case websocketError(Swift.Error)
+
+        var errorDescription: String? {
+            switch self {
+            case .apiNotConfigured:
+                "No server is configured."
+            case .websocketError(let error):
+                error.localizedDescription
+            }
+        }
     }
     
     enum StreamEvent {

ios/QueueCube/Backend/Utilities.swift

@@ -50,8 +50,9 @@ struct RequestBuilder
     }
     
     public func build() -> URLRequest {
-        var request = URLRequest(url: self.url)
+        var request = URLRequest(url: self.url, cachePolicy: .reloadIgnoringLocalCacheData)
         request.httpMethod = self.httpMethod.rawValue
+        request.setValue("no-cache", forHTTPHeaderField: "Cache-Control")
         if let body {
             request.setValue("application/json", forHTTPHeaderField: "Content-Type")
             request.httpBody = body
@@ -61,8 +62,7 @@ struct RequestBuilder
     }
     
     public func json<T: Decodable>() async throws -> T {
-        let urlRequest = self.build()
-        let (data, _) = try await URLSession.shared.data(for: urlRequest)
+        let data = try await responseData()
         return try JSONDecoder().decode(T.self, from: data)
     }
     
@@ -71,13 +71,24 @@ struct RequestBuilder
     }
     
     public func execute() async throws {
-        let urlRequest = self.build()
-        let (data, response) = try await URLSession.shared.data(for: urlRequest)
-        if let httpResponse = response as? HTTPURLResponse {
-            if httpResponse.statusCode != 200 {
-                print("POST error \(httpResponse.statusCode): \(String(data: data, encoding: .utf8)!)")
-            }
+        _ = try await responseData()
+    }
+
+    private func responseData() async throws -> Data {
+        let (data, response) = try await URLSession.shared.data(for: build())
+        guard let httpResponse = response as? HTTPURLResponse else {
+            throw RequestError.invalidResponse
         }
+
+        guard (200..<300).contains(httpResponse.statusCode) else {
+            let serverError = try? JSONDecoder().decode(ServerErrorResponse.self, from: data)
+            throw RequestError.httpError(
+                statusCode: httpResponse.statusCode,
+                message: serverError?.error
+            )
+        }
+
+        return data
     }
     
     public func websocket() -> URL {
@@ -93,6 +104,28 @@ struct RequestBuilder
         case post = "POST"
         case delete = "DELETE"
     }
+
+    private struct ServerErrorResponse: Decodable {
+        let error: String?
+    }
+
+    enum RequestError: Swift.Error, LocalizedError {
+        case invalidResponse
+        case httpError(statusCode: Int, message: String?)
+
+        var errorDescription: String? {
+            switch self {
+            case .invalidResponse:
+                "The server returned an invalid response."
+            case .httpError(let statusCode, let message):
+                if let message, !message.isEmpty {
+                    "Server error (\(statusCode)): \(message)"
+                } else {
+                    "Server error (\(statusCode)): \(HTTPURLResponse.localizedString(forStatusCode: statusCode))"
+                }
+            }
+        }
+    }
 }
 
 extension Color

ios/QueueCube/Views/AddMediaView.swift

@@ -20,12 +20,14 @@ struct AddMediaView: View
                         AutofocusingTextField(String(localized: "ADD_ANY_URL"), text: $model.fieldContents)
                             .autocapitalization(.none)
                             .autocorrectionDisabled()
+                            .frame(minWidth: 0.0, maxWidth: .infinity)
                         
                         PasteButton(payloadType: String.self) { payload in
                             guard let contents = payload.first else { return }
                             model.fieldContents = contents
                         }
                         .labelStyle(.iconOnly)
+                        .fixedSize()
                     }
                 }
                 
@@ -98,6 +100,7 @@ struct SearchMediaView: View
                 
                 AutofocusingTextField(String(localized: "SEARCH_FOR_MEDIA"), text: $searchText, onSubmit: performSearch)
                     .focused($searchFieldFocused)
+                    .frame(minWidth: 0.0, maxWidth: .infinity)
                 
                 if !searchText.isEmpty {
                     Button {

ios/QueueCube/Views/AutofocusingTextField.swift

@@ -29,6 +29,8 @@ struct AutofocusingTextField: UIViewRepresentable
         tf.delegate = context.coordinator
         tf.returnKeyType = .done
         tf.setContentHuggingPriority(.defaultHigh, for: .vertical)
+        tf.setContentHuggingPriority(.defaultLow, for: .horizontal)
+        tf.setContentCompressionResistancePriority(.defaultLow, for: .horizontal)
         tf.autocorrectionType = .no
         tf.autocapitalizationType = .none
         return tf
@@ -64,6 +66,12 @@ struct AutofocusingTextField: UIViewRepresentable
 }
 
 final class FirstResponderTextField: UITextField {
+    override var intrinsicContentSize: CGSize {
+        var size = super.intrinsicContentSize
+        size.width = UIView.noIntrinsicMetric
+        return size
+    }
+
     override func didMoveToSuperview() {
         super.didMoveToSuperview()
         becomeFirstResponder()

ios/QueueCube/Views/ContentView.swift

@@ -24,7 +24,7 @@ struct ContentView: View
             .sheet(isPresented: $model.isNowPlayingSheetPresented) {
                 NowPlayingView(model: model.nowPlayingViewModel)
                     .presentationBackground(.regularMaterial)
-                    .presentationDetents([ .height(320.0) ])
+                    .presentationDetents([ .height(390.0) ])
             }
             .sheet(isPresented: $model.isAddMediaSheetPresented) {
                 AddMediaView(model: $model.addMediaViewModel)
@@ -73,8 +73,13 @@ extension ContentView
                 model.nowPlayingViewModel.title = nowPlaying.playingItem?.title
                 model.nowPlayingViewModel.subtitle = nowPlaying.playingItem?.filename
                 
-                model.nowPlayingViewModel.isPlaying = !nowPlaying.isPaused
                 model.nowPlayingViewModel.volume = Double(nowPlaying.volume) / 100.0
+                model.nowPlayingViewModel.syncPlaybackPosition(
+                    nowPlaying.timePosition,
+                    duration: nowPlaying.duration,
+                    isPlaying: !nowPlaying.isPaused,
+                    isSeekable: nowPlaying.seekable ?? false
+                )
                 model.playlistModel.isPlaying = !nowPlaying.isPaused
                 model.favoritesModel.isPlaying = !nowPlaying.isPaused
             }

ios/QueueCube/Views/MainView.swift

@@ -78,6 +78,14 @@ class MainViewModel
             try await api.previous()
         }
 
+        nowPlayingViewModel.onSeek = { [weak self] model, time in
+            Task {
+                await self?.withModificationsViaAPI { api in
+                    try await api.seek(to: time)
+                }
+            }
+        }
+        
         nowPlayingViewModel.onSheetDismiss = { [weak self] _ in
             self?.isNowPlayingSheetPresented = false
         }
@@ -411,4 +419,3 @@ extension View {
         modifier(ErrorDisplayModifier(error: error))
     }
 }
-

ios/QueueCube/Views/NowPlayingMiniView.swift

@@ -20,6 +20,7 @@ struct NowPlayingMiniView: View {
     
     var body: some View {
         let playPauseImageName = model.isPlaying ? "pause.fill" : "play.fill"
+        let containerShape = RoundedRectangle(cornerRadius: 12.0, style: .continuous)
         let tapGesture = DragGesture(minimumDistance: 0)
             .updating($tapGestureState) { _, state, _ in
                 state = true
@@ -28,41 +29,52 @@ struct NowPlayingMiniView: View {
                 onTap()
             }
 
-        HStack {
-            VStack(alignment: .leading) {
-                if let title = model.title, !title.isEmpty {
-                    Text(title)
-                        .font(.caption)
-                        .lineLimit(1)
-                        .bold()
+        VStack(spacing: 0.0) {
+            HStack {
+                VStack(alignment: .leading) {
+                    if let title = model.title, !title.isEmpty {
+                        Text(title)
+                            .font(.caption)
+                            .lineLimit(1)
+                            .bold()
+                    }
+
+                    if let subtitle = model.subtitle, !subtitle.isEmpty {
+                        Text(subtitle)
+                            .lineLimit(1)
+                            .font(.caption)
+                            .foregroundStyle(.secondary)
+                    }
+
+                    if nothingQueued {
+                        Text(.notPlaying)
+                            .font(.caption)
+                            .foregroundStyle(.secondary)
+                    }
                 }
                 
-                if let subtitle = model.subtitle, !subtitle.isEmpty {
-                    Text(subtitle)
-                        .lineLimit(1)
-                        .font(.caption)
-                        .foregroundStyle(.secondary)
-                }
+                Spacer()
                 
-                if nothingQueued {
-                    Text(.notPlaying)
-                        .font(.caption)
-                        .foregroundStyle(.secondary)
+                Button(action: { model.onPlayPause(model) }) { Image(systemName: playPauseImageName) }
+                    .imageScale(.large)
+                    .padding(12.0)
+            }
+            .padding(EdgeInsets(top: 4.0, leading: 14.0, bottom: 4.0, trailing: 10.0))
+
+            if model.seekablePlaybackDuration != nil {
+                TimelineView(.periodic(from: .now, by: 1.0)) { context in
+                    ProgressView(value: model.playbackProgress(at: context.date) ?? 0.0)
+                        .progressViewStyle(.linear)
+                        .tint(.accentColor)
                 }
             }
-            
-            Spacer()
-            
-            Button(action: { model.onPlayPause(model) }) { Image(systemName: playPauseImageName) }
-                .imageScale(.large)
-                .padding(12.0)
         }
-        .padding(EdgeInsets(top: 4.0, leading: 14.0, bottom: 4.0, trailing: 10.0))
         .background(
-            RoundedRectangle(cornerRadius: 12)
+            containerShape
                 .fill(tapGestureState ? .ultraThinMaterial : .bar)
                 .stroke(.ultraThinMaterial, lineWidth: 1.0)
         )
+        .clipShape(containerShape)
         .shadow(color: .black.opacity(0.15), radius: 14.0, y: 2.0)
         .gesture(tapGesture)
     }

ios/QueueCube/Views/NowPlayingView.swift

@@ -5,6 +5,7 @@
 //  Created by James Magahern on 3/3/25.
 //
 
+import Foundation
 import SwiftUI
 
 @Observable
@@ -14,17 +15,67 @@ class NowPlayingViewModel
     var onStop:         (NowPlayingViewModel) -> Void = { _ in }
     var onNext:         (NowPlayingViewModel) -> Void = { _ in }
     var onPrev:         (NowPlayingViewModel) -> Void = { _ in }
+    var onSeek:         (NowPlayingViewModel, Double) -> Void = { _, _ in }
     var onSheetDismiss: (NowPlayingViewModel) -> Void = { _ in }
     
     var isPlaying: Bool    = false
     var title:     String?  = ""
     var subtitle:  String?  = ""
     var volume:    Double  = 0.5
+    var timePosition: Double?
+    var duration: Double?
+    var isSeekable: Bool = false
     
     fileprivate var isSettingVolume: Bool = false
     fileprivate var settingVolume: Double = 0.0 {
         didSet { volume = settingVolume }
     }
+
+    fileprivate var isSettingPlaybackPosition: Bool = false
+    fileprivate var settingPlaybackPosition: Double = 0.0
+    private var playbackPositionSyncedAt = Date.now
+
+    var playbackDuration: Double? {
+        guard let duration, duration.isFinite, duration > 0 else { return nil }
+        return duration
+    }
+
+    var seekablePlaybackDuration: Double? {
+        guard isSeekable else { return nil }
+        return playbackDuration
+    }
+
+    var displayedPlaybackPosition: Double {
+        displayedPlaybackPosition(at: .now)
+    }
+
+    func displayedPlaybackPosition(at date: Date) -> Double {
+        var position = isSettingPlaybackPosition ? settingPlaybackPosition : (timePosition ?? 0.0)
+        if isPlaying && !isSettingPlaybackPosition {
+            position += max(date.timeIntervalSince(playbackPositionSyncedAt), 0.0)
+        }
+
+        guard position.isFinite else { return 0.0 }
+        return min(max(position, 0.0), playbackDuration ?? position)
+    }
+
+    func playbackProgress(at date: Date) -> Double? {
+        guard let seekablePlaybackDuration else { return nil }
+        return displayedPlaybackPosition(at: date) / seekablePlaybackDuration
+    }
+
+    func syncPlaybackPosition(_ position: Double?, duration: Double?, isPlaying: Bool, isSeekable: Bool) {
+        timePosition = position
+        self.duration = duration
+        self.isPlaying = isPlaying
+        self.isSeekable = isSeekable
+        playbackPositionSyncedAt = .now
+    }
+
+    fileprivate func seekOptimistically(to position: Double) {
+        timePosition = position
+        playbackPositionSyncedAt = .now
+    }
 }
 
 struct NowPlayingView: View
@@ -60,7 +111,31 @@ struct NowPlayingView: View
                     }
                 }
                 
-                Spacer(minLength: 24.0)
+                Spacer(minLength: 20.0)
+
+                if let duration = model.seekablePlaybackDuration {
+                    TimelineView(.periodic(from: .now, by: 1.0)) { context in
+                        VStack(spacing: 2.0) {
+                            Slider(
+                                value: playbackPositionBinding(at: context.date),
+                                in: 0.0...duration,
+                                onEditingChanged: playbackPositionEditingChanged
+                            )
+                            .disabled(nothingQueued)
+
+                            HStack {
+                                Text(formatTime(model.displayedPlaybackPosition(at: context.date)))
+                                Spacer()
+                                Text(formatTime(duration))
+                            }
+                            .font(.caption.monospacedDigit())
+                            .foregroundStyle(.secondary)
+                        }
+                    }
+                    .padding(.horizontal, 4.0)
+
+                    Spacer(minLength: 20.0)
+                }
                 
                 VStack {
                     HStack {
@@ -124,6 +199,38 @@ struct NowPlayingView: View
         }
     }
 
+    private func playbackPositionBinding(at date: Date) -> Binding<Double> {
+        Binding(
+            get: { model.displayedPlaybackPosition(at: date) },
+            set: { model.settingPlaybackPosition = $0 }
+        )
+    }
+
+    private func playbackPositionEditingChanged(_ editing: Bool) {
+        if editing {
+            model.settingPlaybackPosition = model.displayedPlaybackPosition
+            model.isSettingPlaybackPosition = true
+        } else if model.isSettingPlaybackPosition {
+            let position = model.settingPlaybackPosition
+            model.seekOptimistically(to: position)
+            model.isSettingPlaybackPosition = false
+            model.onSeek(model, position)
+        }
+    }
+
+    private func formatTime(_ time: Double) -> String {
+        let totalSeconds = max(Int(time), 0)
+        let hours = totalSeconds / 3_600
+        let minutes = (totalSeconds % 3_600) / 60
+        let seconds = totalSeconds % 60
+
+        if hours > 0 {
+            return String(format: "%d:%02d:%02d", hours, minutes, seconds)
+        }
+
+        return String(format: "%d:%02d", minutes, seconds)
+    }
+    
     // MARK: - Types
     
     private enum Buttons: Int, CaseIterable, Identifiable {

web/backend/src/MediaPlayer.ts

@@ -375,29 +375,27 @@ export class MediaPlayer {
             siteName: "Screen Sharing",
         });
 
-        // Special options for mpv to better handle screen sharing (AI recommended...)
+        // Start from mpv's maintained low-latency profile, then keep only a
+        // couple of frames of demuxed data ready for smooth 60 fps playback.
         await this.loadFile(url, "replace", false, [
-            "demuxer-lavf-o=fflags=+nobuffer+discardcorrupt",  // Reduce buffering and discard corrupt frames
-            "demuxer-lavf-o=analyzeduration=100000",           // Reduce analyze duration
-            "demuxer-lavf-o=probesize=1000000",                // Reduce probe size
-            "untimed=yes",                                     // Ignore timing info
-            "cache=no",                                        // Disable cache
-            "force-seekable=yes",                              // Force seekable
-            "no-cache=yes",                                    // Disable cache
-            "demuxer-max-bytes=500K",                          // Limit demuxer buffer
-            "demuxer-readahead-secs=0.1",                      // Reduce readahead
-            "hr-seek=no",                                      // Disable high-res seeking
-            "video-sync=display-resample",                     // Better sync mode
-            "video-latency-hacks=yes",                         // Enable latency hacks
-            "audio-sync=yes",                                  // Enable audio sync
-            "audio-buffer=0.1",                                // Reduce audio buffer
-            "audio-channels=stereo",                           // Force stereo audio
-            "audio-samplerate=44100",                          // Match sample rate
-            "audio-format=s16",                                // Use 16-bit audio
+            "profile=low-latency",
+            "cache=no",
+            "force-seekable=no",
+            "demuxer-readahead-secs=0.05",
+            "demuxer-max-bytes=256K",
+            "demuxer-mkv-probe-start-time=no",
+            "vd-lavc-threads=2",
+            "vd-lavc-fast=yes",
+            "audio-buffer=0",
+            "pulse-buffer=20",
+            "pipewire-buffer=20",
+            "alsa-buffer-time=20000",
+            "initial-audio-sync=no",
         ]);
 
-        // Make sure it's playing
-        setTimeout(() => this.play(), 100);
+        // loadfile normally unpauses, but make that explicit without adding the
+        // previous fixed 100 ms startup delay.
+        await this.play();
     }
 
     public async play() {
@@ -475,13 +473,18 @@ export class MediaPlayer {
     private async loadFile(url: string, mode: string, fetchMetadata: boolean = true, options: string[] = []) {
         this.lastLoadCandidate = url;
         this.playbackErrors.delete(url);
-        this.modify(UserEvent.PlaylistUpdate, () => this.writeCommand("loadfile", [url, mode, "-1", options.join(',')]));
+        const loadPromise = this.modify(
+            UserEvent.PlaylistUpdate,
+            () => this.writeCommand("loadfile", [url, mode, "-1", options.join(',')]),
+        );
 
         if (fetchMetadata && this.shouldFetchLinkPreview(url)) {
             this.fetchMetadataAndNotify(url).catch(error => {
                 console.warn(`Failed to fetch metadata for ${this.loggableUrl(url)}:`, error);
             });
         }
+
+        await loadPromise;
     }
 
     private async modify<T>(event: UserEvent, func: () => Promise<T>): Promise<T> {

web/backend/src/server.ts

@@ -26,6 +26,7 @@ import { searchInvidious, fetchThumbnail } from "./InvidiousAPI";
 import { PlaylistItem } from './types';
 import { PassThrough } from "stream";
 import { AddressInfo } from "net";
+import { WebSocket } from "ws";
 
 const app = express();
 app.use(express.json());
@@ -43,6 +44,21 @@ const mediaPlayer = new MediaPlayer();
 // Create a shared stream that both endpoints can access
 let activeScreenshareStream: PassThrough | null = null;
 let activeScreenshareMimeType: string | null = null;
+let activeScreenshareSocket: WebSocket | null = null;
+const screenshareStreamsClosedByViewer = new WeakSet<PassThrough>();
+
+const SCREENSHARE_STREAM_HIGH_WATER_MARK = 32 * 1024;
+
+const getScreenshareContentType = (mimeType: unknown): string => {
+    if (typeof mimeType !== "string") {
+        return "application/octet-stream";
+    }
+
+    const contentType = mimeType.split(";", 1)[0].trim().toLowerCase();
+    return contentType === "video/webm" || contentType === "video/mp4"
+        ? contentType
+        : "application/octet-stream";
+};
 
 const withErrorHandling = (func: (req: any, res: any) => Promise<any>) => {
     return async (req: any, res: any) => {
@@ -158,75 +174,104 @@ apiRouter.ws("/events", (ws, req) => {
 // using the fact that QueueCube/MPV is based all around streaming URLs, so the active 
 // screenshare stream manifests as just another URL to play. 
 apiRouter.get("/screenshareStream", withErrorHandling(async (req, res) => {
-    res.setHeader("Content-Type", activeScreenshareMimeType || "video/mp4");
+    const screenshareStream = activeScreenshareStream;
+    if (!screenshareStream) {
+        res.status(503).send("No active screen sharing session");
+        return;
+    }
+
+    req.socket.setNoDelay(true);
+    res.setHeader("Content-Type", activeScreenshareMimeType || "application/octet-stream");
     res.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
     res.setHeader("Pragma", "no-cache");
     res.setHeader("Expires", "0");
     res.setHeader("Connection", "keep-alive");
     res.setHeader("Transfer-Encoding", "chunked");
+    res.setHeader("Accept-Ranges", "none");
+    res.flushHeaders();
 
-    if (!activeScreenshareStream) {
-        res.status(503).send("No active screen sharing session");
-        return;
-    }
-
-    // Handle client disconnection
-    req.on('close', () => {
+    res.on('close', () => {
+        screenshareStream.unpipe(res);
         console.log("Screenshare viewer disconnected");
+
+        // If mpv goes away unexpectedly, stop capture instead of leaving an
+        // unconsumed stream to build backpressure forever.
+        if (activeScreenshareStream === screenshareStream && !screenshareStream.writableEnded) {
+            screenshareStreamsClosedByViewer.add(screenshareStream);
+            activeScreenshareSocket?.close(1011, "Screen sharing viewer disconnected");
+        }
     });
 
-    // Configure stream for low latency
-    activeScreenshareStream.setMaxListeners(0);
-    
-    // Pipe with immediate flush
-    activeScreenshareStream.pipe(res, { end: false });
+    screenshareStream.pipe(res);
 }));
 
 apiRouter.ws("/screenshare", (ws, req) => {
-    const mimeType = req.query.mimeType as string;
+    const mimeType = getScreenshareContentType(req.query.mimeType);
     console.log("Screen sharing client connected with mimeType: " + mimeType);
-    ws.binaryType = "arraybuffer";
+    req.socket.setNoDelay(true);
 
-    let firstChunk = false;
+    // Supersede an old sender without allowing its close handler to tear down
+    // the new session.
+    const previousSocket = activeScreenshareSocket;
+    const previousStream = activeScreenshareStream;
+    activeScreenshareSocket = ws;
+    activeScreenshareMimeType = mimeType;
+    activeScreenshareStream = new PassThrough({
+        highWaterMark: SCREENSHARE_STREAM_HIGH_WATER_MARK,
+        allowHalfOpen: false,
+    });
+    const screenshareStream = activeScreenshareStream;
+    let waitingForDrain = false;
 
-    // Configure WebSocket for low latency
-    ws.setMaxListeners(0);
-    ws.binaryType = "arraybuffer";
+    previousStream?.end();
+    if (previousSocket && previousSocket.readyState === WebSocket.OPEN) {
+        previousSocket.close(1000, "A newer screen sharing session started");
+    }
+
+    // Start mpv while the browser starts its recorder, instead of waiting for a
+    // whole encoded chunk before beginning the HTTP connection and demux setup.
+    const port = (server.address() as AddressInfo).port;
+    const url = `http://127.0.0.1:${port}/api/screenshareStream`;
+    console.log(`Starting screen share stream at ${url}`);
+    mediaPlayer.initiateScreenSharing(url).catch((error: unknown) => {
+        console.error("Failed to start screen sharing:", error);
+        if (activeScreenshareSocket === ws) {
+            ws.close(1011, "Unable to start the media player");
+        }
+    });
 
     ws.on('message', (data: any) => {
         const buffer = data instanceof Buffer ? data : Buffer.from(data);
 
-        if (!firstChunk) {
-            firstChunk = true;
+        if (activeScreenshareStream !== screenshareStream) {
+            return;
+        }
 
-            const port = (server.address() as AddressInfo).port;
-            const url = `http://localhost:${port}/api/screenshareStream`;
-            console.log(`Starting screen share stream at ${url}`);
-            
-            // Create new shared stream with immediate flush
-            activeScreenshareStream = new PassThrough({
-                highWaterMark: 1024 * 1024, // 1MB buffer
-                allowHalfOpen: false
-            });
-            
-            activeScreenshareStream.write(buffer);
-            mediaPlayer.initiateScreenSharing(url);
-        } else if (activeScreenshareStream) {
-            // Write with immediate flush
-            activeScreenshareStream.write(buffer, () => {
-                activeScreenshareStream?.cork();
-                activeScreenshareStream?.uncork();
+        if (!screenshareStream.write(buffer) && !waitingForDrain) {
+            waitingForDrain = true;
+            ws.pause();
+            screenshareStream.once('drain', () => {
+                waitingForDrain = false;
+                if (activeScreenshareStream === screenshareStream && ws.readyState === WebSocket.OPEN) {
+                    ws.resume();
+                }
             });
         }
     });
 
     ws.on('close', () => {
         console.log("Screen sharing client disconnected");
-        if (activeScreenshareStream) {
-            activeScreenshareStream.end();
+        if (activeScreenshareStream === screenshareStream) {
+            screenshareStream.end();
             activeScreenshareStream = null;
+            activeScreenshareMimeType = null;
+            activeScreenshareSocket = null;
+            if (!screenshareStreamsClosedByViewer.has(screenshareStream)) {
+                mediaPlayer.stop().catch((error: unknown) => {
+                    console.error("Failed to stop screen sharing:", error);
+                });
+            }
         }
-        mediaPlayer.stop();
     });
 });
 

web/frontend/src/api/player.tsx

@@ -203,7 +203,9 @@ export const API = {
 
   startScreenShare(mimeType: string): WebSocket {
     const protocol = window.location.protocol === 'https:' ? 'wss' : 'ws';
-    const ws = new WebSocket(`${protocol}://${window.location.host}/api/screenshare?mimeType=${mimeType}`);
+    const ws = new WebSocket(
+      `${protocol}://${window.location.host}/api/screenshare?mimeType=${encodeURIComponent(mimeType)}`,
+    );
     return ws;
   }
 };

web/frontend/src/hooks/useScreenShare.ts

@@ -1,6 +1,17 @@
 import { useState, useEffect, useRef, useCallback } from 'react';
 import { API } from '../api/player';
 
+const TARGET_FRAME_RATE = 60;
+const MAX_CAPTURE_WIDTH = 1920;
+const MAX_CAPTURE_HEIGHT = 1080;
+const RECORDER_TIMESLICE_MS = 16;
+const MIN_VIDEO_BIT_RATE = 2_500_000;
+const MAX_VIDEO_BIT_RATE = 8_000_000;
+const VIDEO_BITS_PER_PIXEL = 0.065;
+const SOCKET_BUFFER_TARGET_MS = 75;
+const MIN_SOCKET_BUFFER_BYTES = 32 * 1024;
+const MIN_RESUME_BUFFER_BYTES = 8 * 1024;
+
 interface UseScreenShareResult {
   isScreenSharing: boolean;
   isScreenSharingSupported: boolean;
@@ -8,15 +19,21 @@ interface UseScreenShareResult {
   stopScreenShare: () => void;
 }
 
-function getBestSupportedMimeType() {
-  // Ordered by preference (best first) - all of these include audio+video
-  const mimeTypes = [
-    'video/webm;codecs=vp9,opus',     // Best quality, good compression
-    'video/webm;codecs=vp8,opus',     // Good fallback, well supported
-    'video/webm;codecs=h264,opus',    // Better compatibility with some systems
-    'video/mp4;codecs=h264,aac',      // Good for Safari but may not be supported for MediaRecorder
-    'video/webm',                     // Generic fallback (browser will choose codecs)
-    'video/mp4'                       // Last resort
+function getBestSupportedMimeType(hasAudio: boolean): string | undefined {
+  // VP8 is substantially cheaper to encode than VP9 on most systems. Prefer it
+  // for real-time capture, then use hardware-friendly H.264 where available.
+  const mimeTypes = hasAudio ? [
+    'video/webm;codecs=vp8,opus',
+    'video/mp4;codecs=avc1.42E01E,mp4a.40.2',
+    'video/webm;codecs=vp9,opus',
+    'video/webm',
+    'video/mp4',
+  ] : [
+    'video/webm;codecs=vp8',
+    'video/mp4;codecs=avc1.42E01E',
+    'video/webm;codecs=vp9',
+    'video/webm',
+    'video/mp4',
   ];
 
   // Find the first supported mimetype
@@ -27,15 +44,42 @@ function getBestSupportedMimeType() {
     }
   }
 
-  // If none are supported, return null or a basic fallback
   console.warn('No preferred mime types supported by this browser');
-  return 'video/webm'; // Most basic fallback
+  return undefined;
+}
+
+function getTargetVideoBitRate(track: MediaStreamTrack): number {
+  const settings = track.getSettings();
+  const width = settings.width ?? MAX_CAPTURE_WIDTH;
+  const height = settings.height ?? MAX_CAPTURE_HEIGHT;
+  const frameRate = Math.min(settings.frameRate ?? TARGET_FRAME_RATE, TARGET_FRAME_RATE);
+  const target = width * height * frameRate * VIDEO_BITS_PER_PIXEL;
+
+  return Math.round(Math.min(MAX_VIDEO_BIT_RATE, Math.max(MIN_VIDEO_BIT_RATE, target)));
+}
+
+function getSocketBufferLimits(recorder: MediaRecorder) {
+  const bytesPerSecond = (recorder.videoBitsPerSecond + recorder.audioBitsPerSecond) / 8;
+  const maximum = Math.max(
+    MIN_SOCKET_BUFFER_BYTES,
+    Math.ceil(bytesPerSecond * SOCKET_BUFFER_TARGET_MS / 1000),
+  );
+
+  return {
+    maximum,
+    resumeAt: Math.max(MIN_RESUME_BUFFER_BYTES, Math.floor(maximum / 4)),
+  };
 }
 
 export const useScreenShare = (): UseScreenShareResult => {
   const [isScreenSharing, setIsScreenSharing] = useState(false);
   const [isScreenSharingSupported, setIsScreenSharingSupported] = useState(false);
   const screenShareSocketRef = useRef<WebSocket | null>(null);
+  const mediaRecorderRef = useRef<MediaRecorder | null>(null);
+  const mediaStreamRef = useRef<MediaStream | null>(null);
+  const backpressureTimerRef = useRef<number | null>(null);
+  const isStartingRef = useRef(false);
+  const sessionGenerationRef = useRef(0);
 
   // Check if screen sharing is supported
   useEffect(() => {
@@ -47,80 +91,205 @@ export const useScreenShare = (): UseScreenShareResult => {
   }, []);
 
   const stopScreenShare = useCallback(() => {
-    if (screenShareSocketRef.current) {
-      screenShareSocketRef.current.close();
-      screenShareSocketRef.current = null;
+    sessionGenerationRef.current += 1;
+    isStartingRef.current = false;
+
+    if (backpressureTimerRef.current !== null) {
+      window.clearInterval(backpressureTimerRef.current);
+      backpressureTimerRef.current = null;
     }
+
+    const recorder = mediaRecorderRef.current;
+    mediaRecorderRef.current = null;
+    if (recorder) {
+      recorder.ondataavailable = null;
+      recorder.onerror = null;
+      if (recorder.state !== 'inactive') {
+        recorder.stop();
+      }
+    }
+
+    const mediaStream = mediaStreamRef.current;
+    mediaStreamRef.current = null;
+    mediaStream?.getTracks().forEach((track) => {
+      track.onended = null;
+      track.stop();
+    });
+
+    const socket = screenShareSocketRef.current;
+    screenShareSocketRef.current = null;
+    if (socket) {
+      socket.onopen = null;
+      socket.onclose = null;
+      socket.onerror = null;
+      if (socket.readyState === WebSocket.CONNECTING || socket.readyState === WebSocket.OPEN) {
+        socket.close();
+      }
+    }
+
     setIsScreenSharing(false);
   }, []);
 
   const startScreenShare = useCallback(async () => {
+    if (isStartingRef.current || screenShareSocketRef.current) {
+      return;
+    }
+
+    isStartingRef.current = true;
+    const sessionGeneration = ++sessionGenerationRef.current;
+
     try {
       const mediaStream = await navigator.mediaDevices.getDisplayMedia({
-        video: true,
+        video: {
+          frameRate: { ideal: TARGET_FRAME_RATE, max: TARGET_FRAME_RATE },
+          width: { max: MAX_CAPTURE_WIDTH },
+          height: { max: MAX_CAPTURE_HEIGHT },
+        },
         audio: true,
       });
 
-      let mimeType = getBestSupportedMimeType();
-      console.log('Using MIME type:', mimeType);
+      // getDisplayMedia cannot be programmatically dismissed. If the user
+      // stopped or restarted while its picker was open, discard this result.
+      if (sessionGenerationRef.current !== sessionGeneration) {
+        mediaStream.getTracks().forEach((track) => track.stop());
+        return;
+      }
 
-      const mediaRecorder = new MediaRecorder(mediaStream, {
-        mimeType: mimeType,
-        videoBitsPerSecond: 2500000, // 2.5 Mbps
-        audioBitsPerSecond: 128000,  // 128 kbps
+      mediaStreamRef.current = mediaStream;
+
+      const videoTrack = mediaStream.getVideoTracks()[0];
+      if (!videoTrack) {
+        throw new Error('The selected source did not provide a video track');
+      }
+
+      // Favor smooth motion over static-text quality when the browser needs to
+      // trade capture resolution for frame rate.
+      videoTrack.contentHint = 'motion';
+      mediaStream.getAudioTracks().forEach((track) => {
+        track.contentHint = 'music';
       });
 
+      const hasAudio = mediaStream.getAudioTracks().length > 0;
+      const preferredMimeType = getBestSupportedMimeType(hasAudio);
+      const recorderOptions: MediaRecorderOptions = {
+        videoBitsPerSecond: getTargetVideoBitRate(videoTrack),
+      };
+
+      if (preferredMimeType) {
+        recorderOptions.mimeType = preferredMimeType;
+      }
+      if (hasAudio) {
+        recorderOptions.audioBitsPerSecond = 128_000;
+      }
+
+      const mediaRecorder = new MediaRecorder(mediaStream, recorderOptions);
+      mediaRecorderRef.current = mediaRecorder;
+      const mimeType = mediaRecorder.mimeType || preferredMimeType || 'application/octet-stream';
+      const socketBufferLimits = getSocketBufferLimits(mediaRecorder);
+      console.log(
+        `Screen sharing at up to ${TARGET_FRAME_RATE} fps, ${Math.round(mediaRecorder.videoBitsPerSecond / 1000)} kbps, using ${mimeType}`,
+      );
+
       // Connect to WebSocket
-      screenShareSocketRef.current = API.startScreenShare(mimeType);
+      const socket = API.startScreenShare(mimeType);
+      screenShareSocketRef.current = socket;
+      isStartingRef.current = false;
+
+      const resumeRecorderWhenDrained = () => {
+        if (screenShareSocketRef.current !== socket || mediaRecorderRef.current !== mediaRecorder) {
+          if (backpressureTimerRef.current !== null) {
+            window.clearInterval(backpressureTimerRef.current);
+            backpressureTimerRef.current = null;
+          }
+          return;
+        }
+
+        if (socket.bufferedAmount <= socketBufferLimits.resumeAt && mediaRecorder.state === 'paused') {
+          mediaRecorder.resume();
+          if (backpressureTimerRef.current !== null) {
+            window.clearInterval(backpressureTimerRef.current);
+            backpressureTimerRef.current = null;
+          }
+        }
+      };
+
+      const pauseRecorderForBackpressure = () => {
+        if (mediaRecorder.state === 'recording') {
+          mediaRecorder.pause();
+        }
+
+        if (backpressureTimerRef.current === null) {
+          backpressureTimerRef.current = window.setInterval(
+            resumeRecorderWhenDrained,
+            RECORDER_TIMESLICE_MS,
+          );
+        }
+      };
 
       // Set up WebSocket event handlers
-      screenShareSocketRef.current.onopen = () => {
+      socket.onopen = () => {
+        if (screenShareSocketRef.current !== socket) {
+          socket.close();
+          return;
+        }
+
         console.log('Screen sharing WebSocket connected');
         setIsScreenSharing(true);
-
-        mediaRecorder.start(100);
+        mediaRecorder.start(RECORDER_TIMESLICE_MS);
       };
 
-      screenShareSocketRef.current.onclose = () => {
+      socket.onclose = () => {
         console.log('Screen sharing WebSocket closed');
-        setIsScreenSharing(false);
-
-        // Stop all tracks when WebSocket is closed
-        mediaStream.getTracks().forEach(track => track.stop());
+        if (screenShareSocketRef.current === socket) {
+          stopScreenShare();
+        }
       };
 
-      screenShareSocketRef.current.onerror = (error) => {
+      socket.onerror = (error) => {
         console.error('Screen sharing WebSocket error:', error);
-        setIsScreenSharing(false);
+        if (screenShareSocketRef.current === socket) {
+          stopScreenShare();
+        }
+      };
 
-        // Stop all tracks on error
-        mediaStream.getTracks().forEach(track => track.stop());
+      mediaRecorder.onerror = (error) => {
+        console.error('Screen sharing recorder error:', error);
+        if (mediaRecorderRef.current === mediaRecorder) {
+          stopScreenShare();
+        }
       };
 
       // Send data over WebSocket when available
       mediaRecorder.ondataavailable = (event) => {
-        if (event.data && event.data.size > 0 && screenShareSocketRef.current && screenShareSocketRef.current.readyState === WebSocket.OPEN) {
-          screenShareSocketRef.current.send(event.data);
+        if (event.data.size > 0 && screenShareSocketRef.current === socket && socket.readyState === WebSocket.OPEN) {
+          socket.send(event.data);
+
+          // Browser WebSockets otherwise queue without a limit, turning a brief
+          // network slowdown into permanently stale playback. Pausing capture
+          // bounds that queue and resumes at the live edge once it drains.
+          if (socket.bufferedAmount >= socketBufferLimits.maximum) {
+            pauseRecorderForBackpressure();
+          }
         }
       };
 
       // Handle stream ending (user clicks "Stop sharing")
-      mediaStream.getVideoTracks()[0].onended = () => {
-        if (screenShareSocketRef.current) {
-          screenShareSocketRef.current.close();
-          screenShareSocketRef.current = null;
-        }
-        setIsScreenSharing(false);
-      };
+      videoTrack.onended = stopScreenShare;
 
     } catch (error) {
-      console.error('Error starting screen share:', error);
-      setIsScreenSharing(false);
+      if (sessionGenerationRef.current === sessionGeneration) {
+        console.error('Error starting screen share:', error);
+        stopScreenShare();
+      }
     }
-  }, []);
+  }, [stopScreenShare]);
+
+  useEffect(() => {
+    return () => stopScreenShare();
+  }, [stopScreenShare]);
 
   const toggleScreenShare = useCallback(async () => {
-    if (screenShareSocketRef.current) {
+    if (screenShareSocketRef.current || isStartingRef.current) {
       stopScreenShare();
     } else {
       await startScreenShare();