fix: update innertube clients and fix HLS/DASH quality switching

- Update innertube client versions to match yt-dlp (android 21.02.35,
  ios 21.02.3, web 2.20260114.08.00, android_vr 1.65.10)
- Remove obsolete clients (android-test-suite, ios_vr)
- Replace tv_embedded with TVHTML5_SIMPLY (cn 75)
- Add new clients: web_embedded, mweb, tv
- Fix HLS freeze on quality switch: use nextLevel instead of
  currentLevel, handle bufferStalledError, stream proxy segments
  instead of buffering in memory
- Populate DASH quality selector with actual sources (no Auto)
- Render quality-select empty in template, let JS populate per mode

youtube/static/js/watch.dash.js

@@ -31,9 +31,34 @@ if (data.using_pair_sources) {
     avMerge = new AVMerge(video, srcPair, 0);
 }
 
-// Quality selector
+// Quality selector — populate with available sources
 const qs = document.getElementById('quality-select');
 if (qs) {
+  // Clear the HLS-oriented "Auto" default; DASH has discrete sources
+  qs.innerHTML = '';
+
+  // Add pair_sources (video+audio, used by AVMerge)
+  if (data['pair_sources'] && data['pair_sources'].length) {
+    data['pair_sources'].forEach(function(src, i) {
+      let opt = document.createElement('option');
+      opt.value = JSON.stringify({type: 'pair', index: i});
+      opt.textContent = src.quality_string;
+      if (i === data['pair_idx']) opt.selected = true;
+      qs.appendChild(opt);
+    });
+  }
+
+  // Add uni_sources (integrated video+audio, single file)
+  if (data['uni_sources'] && data['uni_sources'].length) {
+    data['uni_sources'].forEach(function(src, i) {
+      let opt = document.createElement('option');
+      opt.value = JSON.stringify({type: 'uni', index: i});
+      opt.textContent = src.quality_string;
+      if (!data['pair_sources'].length && i === data['uni_idx']) opt.selected = true;
+      qs.appendChild(opt);
+    });
+  }
+
   qs.addEventListener('change', function(e) {
     changeQuality(JSON.parse(this.value))
   });

youtube/static/js/watch.hls.js

@@ -26,7 +26,17 @@ function initHLSNative(manifestUrl) {
             lowLatencyMode: false,
             maxBufferLength: 30,
             maxMaxBufferLength: 60,
+            maxBufferHole: 0.5,
             startLevel: -1,
+            // Prevent stalls on quality switch: nudge playback past small gaps
+            nudgeMaxRetry: 5,
+            // Allow more time for segments coming through our proxy
+            fragLoadingTimeOut: 30000,
+            fragLoadingMaxRetry: 5,
+            fragLoadingRetryDelay: 1000,
+            levelLoadingTimeOut: 15000,
+            levelLoadingMaxRetry: 4,
+            levelLoadingRetryDelay: 1000,
         });
 
         window.hls = hls;
@@ -89,15 +99,26 @@ function initHLSNative(manifestUrl) {
                 console.error('HLS fatal error:', data.type, data.details);
                 switch(data.type) {
                     case Hls.ErrorTypes.NETWORK_ERROR:
+                        console.warn('HLS network error, attempting recovery...');
                         hls.startLoad();
                         break;
                     case Hls.ErrorTypes.MEDIA_ERROR:
+                        console.warn('HLS media error, attempting recovery...');
                         hls.recoverMediaError();
                         break;
                     default:
                         hls.destroy();
                         break;
                 }
+            } else {
+                // Non-fatal errors can still cause stalls, especially
+                // bufferStalledError after a quality switch through our proxy
+                console.warn('HLS non-fatal error:', data.type, data.details);
+                if (data.details === 'bufferStalledError') {
+                    // Buffer ran dry — HLS.js is waiting for data.
+                    // Nudge it to retry loading the current fragment.
+                    hls.startLoad();
+                }
             }
         });
 
@@ -122,13 +143,36 @@ function initPlayer() {
     initHLSNative(hls_manifest_url);
 
     const qualitySelect = document.getElementById('quality-select');
+    // Set initial Auto option while manifest loads
+    if (qualitySelect) {
+        qualitySelect.innerHTML = '<option value="-1" selected>Auto</option>';
+    }
     if (qualitySelect) {
         qualitySelect.addEventListener('change', function () {
             const level = parseInt(this.value);
 
             if (hls) {
-                hls.currentLevel = level;
-                console.log('Quality:', level === -1 ? 'Auto' : hls.levels[level]?.height + 'p');
+                const currentTime = video.currentTime;
+                const wasPaused = video.paused;
+
+                // Use nextLevel for smoother transition: it waits for the
+                // current segment to finish before switching, avoiding an
+                // abrupt buffer flush that starves the player.
+                if (level === -1) {
+                    // Back to auto — re-enable ABR
+                    hls.currentLevel = -1;
+                    console.log('Quality: Auto (ABR)');
+                } else {
+                    hls.nextLevel = level;
+                    console.log('Quality: switching to',
+                                hls.levels[level]?.height + 'p');
+                }
+
+                // If the video was already stalled, kick the loader
+                // so it starts fetching the new level immediately.
+                if (video.readyState < 3) {
+                    hls.startLoad(currentTime);
+                }
             }
         });
     }