Fix for dynacast error

Author: MaxHeimbrock

livekit/src/room/track/local_video_track.rs

@@ -370,17 +370,19 @@ impl LocalVideoTrack {
 
         let mut changed = false;
         for encoding in &mut params.encodings {
-            let quality = crate::options::video_quality_for_rid_or_default(&encoding.rid);
+            // The SFU addresses layers by spatial index (0 = Low), so a
+            // single rid-less encoding is addressed as Low, not High.
+            let rid = if encoding.rid.is_empty() { "q" } else { encoding.rid.as_str() };
+            let quality = crate::options::video_quality_for_rid_or_default(rid);
 
-            let should_active = qualities
-                .iter()
-                .find(|q| q.quality == quality as i32)
-                .map(|q| q.enabled)
-                .unwrap_or(false);
+            // A quality missing from the update is left untouched.
+            let Some(subscribed) = qualities.iter().find(|q| q.quality == quality as i32) else {
+                continue;
+            };
 
-            if encoding.active != should_active {
+            if encoding.active != subscribed.enabled {
                 changed = true;
-                encoding.active = should_active;
+                encoding.active = subscribed.enabled;
             }
         }
 
@@ -394,11 +396,10 @@ impl LocalVideoTrack {
             })
             .collect();
 
-        sender
-            .set_parameters(params)
-            .map_err(|e| RoomError::Internal(format!("failed to set sender parameters: {}", e)))?;
-
         if changed {
+            sender.set_parameters(params).map_err(|e| {
+                RoomError::Internal(format!("failed to set sender parameters: {}", e))
+            })?;
             log::debug!("dynacast: layers changed -> [{}]", layers.join(", "));
         } else {
             log::debug!("dynacast: layers unchanged [{}]", layers.join(", "));