From 1887c262d5d76dabfbea1097ed4f00a514023b77 Mon Sep 17 00:00:00 2001
From: Yiannis Christodoulou <yiannis@web357.com>
Date: Sat, 18 Oct 2025 22:00:20 +0300
Subject: [PATCH] Improve subtitle restoration for mobile devices

Increases subtitle restoration attempts and uses exponential backoff to better support mobile devices where text tracks may load slowly. Adds logic to only warn when subtitle tracks are present but the desired language is not found, and improves error handling for native text track access.
---
 .../video-js/src/utils/UserPreferences.js     | 37 ++++++++++++++++---
 1 file changed, 31 insertions(+), 6 deletions(-)

diff --git a/frontend-tools/video-js/src/utils/UserPreferences.js b/frontend-tools/video-js/src/utils/UserPreferences.js
index 9d45de02..b3224968 100644
--- a/frontend-tools/video-js/src/utils/UserPreferences.js
+++ b/frontend-tools/video-js/src/utils/UserPreferences.js
@@ -340,9 +340,28 @@ class UserPreferences {
             // Set flag to prevent auto-save during restoration
             this.isRestoringSubtitles = true;
             // Multiple attempts with increasing delays to ensure text tracks are loaded
+            // Mobile devices need more time and attempts
+            const maxAttempts = 10; // Increased from 5 for mobile compatibility
             const attemptToApplySubtitles = (attempt = 1) => {
                 const textTracks = player.textTracks();
 
+                // Check if we have any subtitle tracks loaded yet
+                let hasSubtitleTracks = false;
+                for (let i = 0; i < textTracks.length; i++) {
+                    if (textTracks[i].kind === 'subtitles') {
+                        hasSubtitleTracks = true;
+                        break;
+                    }
+                }
+
+                // If no subtitle tracks found yet and we have attempts left, retry with longer delay
+                if (!hasSubtitleTracks && attempt < maxAttempts) {
+                    // Use exponential backoff: 100ms, 200ms, 400ms, 800ms, etc.
+                    const delay = Math.min(100 * Math.pow(1.5, attempt - 1), 1000);
+                    setTimeout(() => attemptToApplySubtitles(attempt + 1), delay);
+                    return;
+                }
+
                 // First, disable all subtitle tracks
                 for (let i = 0; i < textTracks.length; i++) {
                     const track = textTracks[i];
@@ -401,13 +420,17 @@ class UserPreferences {
                 // Clear the restoration flag after a longer delay to ensure all events have settled
                 setTimeout(() => {
                     this.isRestoringSubtitles = false;
-                }, 600); // Increased to 3 seconds
+                }, 600);
 
-                // If not found and we haven't tried too many times, try again
-                if (!found && attempt < 5) {
-                    setTimeout(() => attemptToApplySubtitles(attempt + 1), attempt * 50);
+                // If not found and we haven't tried too many times, try again with longer delay
+                if (!found && attempt < maxAttempts) {
+                    const delay = Math.min(100 * Math.pow(1.5, attempt - 1), 1000);
+                    setTimeout(() => attemptToApplySubtitles(attempt + 1), delay);
                 } else if (!found) {
-                    console.warn('Could not find subtitle track for language:', savedLanguage);
+                    // Only log warning if we had subtitle tracks but couldn't match the language
+                    if (hasSubtitleTracks) {
+                        console.warn('Could not find subtitle track for language:', savedLanguage);
+                    }
                     // Clear flag even if not found
                     this.isRestoringSubtitles = false;
                 }
@@ -428,7 +451,9 @@ class UserPreferences {
                     ttList.addEventListener('addtrack', onAddTrack, { once: true });
                     ttList.addEventListener('change', onChange, { once: true });
                 }
-            } catch (e) {}
+            } catch {
+                // Silently ignore errors accessing native text track list
+            }
         } else {
             // Ensure subtitles are off on load when not enabled
             try {