feat(video quality): add maxFullResolutionParticipants (#7403)

Add a config option with the default value of 2, which will cap the max recv video quality to SD if there's more than 2 participants in the conference while in the tile view mode.

config.js

     // Sets the preferred resolution (height) for local video. Defaults to 720.
     // resolution: 720,
 
+    // How many participants while in the tile view mode, before the receiving video quality is reduced from HD to SD.
+    // Use -1 to disable.
+    // maxFullResolutionParticipants: 2
+
     // w3c spec-compliant video constraints to use for video capture. Currently
     // used by browsers that return true from lib-jitsi-meet's
     // util#browser#usesNewGumFlow. The constraints are independent from

react/features/base/config/configWhitelist.js

     'ignoreStartMuted',
     'liveStreamingEnabled',
     'localRecording',
+    'maxFullResolutionParticipants',
     'minParticipants',
     'nick',
     'openBridgeChannel',

react/features/video-quality/middleware.js

     setMaxReceiverVideoQuality,
     setPreferredVideoQuality
 } from '../base/conference';
+import { getParticipantCount } from '../base/participants';
 import { MiddlewareRegistry, StateListenerRegistry } from '../base/redux';
 import { shouldDisplayTileView } from '../video-layout';
 
         const { reducedUI } = state['features/base/responsive-ui'];
         const _shouldDisplayTileView = shouldDisplayTileView(state);
         const thumbnailSize = state['features/filmstrip']?.tileViewDimensions?.thumbnailSize;
+        const participantCount = getParticipantCount(state);
 
         return {
             displayTileView: _shouldDisplayTileView,
+            participantCount,
             reducedUI,
             thumbnailHeight: thumbnailSize?.height
         };
     },
-    /* listener */ ({ displayTileView, reducedUI, thumbnailHeight }, { dispatch, getState }) => {
-        const { maxReceiverVideoQuality } = getState()['features/base/conference'];
+    /* listener */ ({ displayTileView, participantCount, reducedUI, thumbnailHeight }, { dispatch, getState }) => {
+        const state = getState();
+        const { maxReceiverVideoQuality } = state['features/base/conference'];
+        const { maxFullResolutionParticipants = 2 } = state['features/base/config'];
+
         let newMaxRecvVideoQuality = VIDEO_QUALITY_LEVELS.HIGH;
 
         if (reducedUI) {
             newMaxRecvVideoQuality = VIDEO_QUALITY_LEVELS.LOW;
         } else if (displayTileView && !Number.isNaN(thumbnailHeight)) {
             newMaxRecvVideoQuality = getNearestReceiverVideoQualityLevel(thumbnailHeight);
+
+            // Override HD level calculated for the thumbnail height when # of participants threshold is exceeded
+            if (maxReceiverVideoQuality !== newMaxRecvVideoQuality && maxFullResolutionParticipants !== -1) {
+                const override
+                    = participantCount > maxFullResolutionParticipants
+                        && newMaxRecvVideoQuality > VIDEO_QUALITY_LEVELS.STANDARD;
+
+                logger.info(`The nearest receiver video quality level for thumbnail height: ${thumbnailHeight}, `
+                    + `is: ${newMaxRecvVideoQuality}, `
+                    + `override: ${String(override)}, `
+                    + `max full res N: ${maxFullResolutionParticipants}`);
+
+                if (override) {
+                    newMaxRecvVideoQuality = VIDEO_QUALITY_LEVELS.STANDARD;
+                }
+            }
         }
 
         if (maxReceiverVideoQuality !== newMaxRecvVideoQuality) {