diff --git a/libs/hbb_common/protos/message.proto b/libs/hbb_common/protos/message.proto
index ca12eb908..dac137e1c 100644
--- a/libs/hbb_common/protos/message.proto
+++ b/libs/hbb_common/protos/message.proto
@@ -663,6 +663,7 @@ message Misc {
     PluginRequest plugin_request = 25;
     PluginFailure plugin_failure = 26;
     uint32 full_speed_fps = 27;
+    uint32 auto_adjust_fps = 28;
   }
 }
 
diff --git a/libs/scrap/src/common/codec.rs b/libs/scrap/src/common/codec.rs
index 84eb1c43e..fac5f82d7 100644
--- a/libs/scrap/src/common/codec.rs
+++ b/libs/scrap/src/common/codec.rs
@@ -535,11 +535,10 @@ pub fn codec_thread_num() -> usize {
         info = format!("cpu loadavg:{}", avg.one);
         res = (((max as f64) - avg.one) * 0.5).round() as usize;
     }
-    res = if res > 0 && res <= max / 2 {
-        res
-    } else {
-        std::cmp::max(1, max / 2)
-    };
+    res = std::cmp::min(res, max / 2);
+    if res == 0 {
+        res = 1;
+    }
     // avoid frequent log
     let log = match THREAD_LOG_TIME.lock().unwrap().clone() {
         Some(instant) => instant.elapsed().as_secs() > 1,
diff --git a/src/client/io_loop.rs b/src/client/io_loop.rs
index fb0bba5a9..b4e311227 100644
--- a/src/client/io_loop.rs
+++ b/src/client/io_loop.rs
@@ -895,7 +895,9 @@ impl<T: InvokeUiSession> Remote<T> {
         }
         // decrease judgement
         let debounce = if decode_fps > 10 { decode_fps / 2 } else { 5 }; // 500ms
-        let should_decrease = len >= debounce && len > ctl.last_queue_size + 5; // exceed debounce or still caching
+        let should_decrease = len >= debounce // exceed debounce
+            && len > ctl.last_queue_size + 5 // still caching
+            && !ctl.last_custom_fps.unwrap_or(i32::MAX) < limited_fps as i32; // NOT already set a smaller one
 
         // increase judgement
         if len <= 1 {
@@ -919,10 +921,15 @@ impl<T: InvokeUiSession> Remote<T> {
             }
             // send custom fps
             let mut misc = Misc::new();
-            misc.set_option(OptionMessage {
-                custom_fps,
-                ..Default::default()
-            });
+            if version > hbb_common::get_version_number("1.2.1") {
+                // avoid confusion with custom image quality fps
+                misc.set_auto_adjust_fps(custom_fps as _);
+            } else {
+                misc.set_option(OptionMessage {
+                    custom_fps,
+                    ..Default::default()
+                });
+            }
             let mut msg = Message::new();
             msg.set_misc(misc);
             self.sender.send(Data::Message(msg)).ok();
diff --git a/src/server/connection.rs b/src/server/connection.rs
index 39a87547e..cb993301e 100644
--- a/src/server/connection.rs
+++ b/src/server/connection.rs
@@ -1940,6 +1940,10 @@ impl Connection {
                         .lock()
                         .unwrap()
                         .user_full_speed_fps(self.inner.id(), fps),
+                    Some(misc::Union::AutoAdjustFps(fps)) => video_service::VIDEO_QOS
+                        .lock()
+                        .unwrap()
+                        .user_auto_adjust_fps(self.inner.id(), fps),
                     _ => {}
                 },
                 Some(message::Union::AudioFrame(frame)) => {
diff --git a/src/server/video_qos.rs b/src/server/video_qos.rs
index 18b5f50de..dda15fd55 100644
--- a/src/server/video_qos.rs
+++ b/src/server/video_qos.rs
@@ -31,6 +31,7 @@ struct Delay {
 #[derive(Default, Debug, Copy, Clone)]
 struct UserData {
     full_speed_fps: Option<u32>,
+    auto_adjust_fps: Option<u32>,
     custom_fps: Option<u32>,
     quality: Option<(i64, Quality)>, // (time, quality)
     delay: Option<Delay>,
@@ -90,11 +91,15 @@ pub enum RefreshType {
 
 impl VideoQoS {
     pub fn spf(&self) -> Duration {
-        Duration::from_secs_f32(1. / (self.fps as f32))
+        Duration::from_secs_f32(1. / (self.fps() as f32))
     }
 
     pub fn fps(&self) -> u32 {
-        self.fps
+        if self.fps >= MIN_FPS && self.fps <= MAX_FPS {
+            self.fps
+        } else {
+            FPS
+        }
     }
 
     pub fn store_bitrate(&mut self, bitrate: u32) {
@@ -118,6 +123,12 @@ impl VideoQoS {
         let user_fps = |u: &UserData| {
             // full_speed_fps
             let mut fps = u.full_speed_fps.unwrap_or_default() * 9 / 10;
+            // auto adjust fps
+            if let Some(auto_adjust_fps) = u.auto_adjust_fps {
+                if fps == 0 || auto_adjust_fps < fps {
+                    fps = auto_adjust_fps;
+                }
+            }
             // custom_fps
             if let Some(custom_fps) = u.custom_fps {
                 if fps == 0 || custom_fps < fps {
@@ -128,7 +139,7 @@ impl VideoQoS {
             if let Some(delay) = u.delay {
                 fps = match delay.state {
                     DelayState::Normal => fps,
-                    DelayState::LowDelay => fps,
+                    DelayState::LowDelay => fps * 3 / 4,
                     DelayState::HighDelay => fps / 2,
                     DelayState::Broken => fps / 4,
                 }
@@ -181,7 +192,11 @@ impl VideoQoS {
             if delay != DelayState::Normal {
                 match self.quality {
                     Quality::Best => {
-                        quality = Quality::Balanced;
+                        quality = if delay == DelayState::Broken {
+                            Quality::Low
+                        } else {
+                            Quality::Balanced
+                        };
                     }
                     Quality::Balanced => {
                         quality = Quality::Low;
@@ -259,6 +274,21 @@ impl VideoQoS {
         self.refresh(None);
     }
 
+    pub fn user_auto_adjust_fps(&mut self, id: i32, fps: u32) {
+        if let Some(user) = self.users.get_mut(&id) {
+            user.auto_adjust_fps = Some(fps);
+        } else {
+            self.users.insert(
+                id,
+                UserData {
+                    auto_adjust_fps: Some(fps),
+                    ..Default::default()
+                },
+            );
+        }
+        self.refresh(None);
+    }
+
     pub fn user_image_quality(&mut self, id: i32, image_quality: i32) {
         // https://github.com/rustdesk/rustdesk/blob/d716e2b40c38737f1aa3f16de0dec67394a6ac68/src/server/video_service.rs#L493
         let convert_quality = |q: i32| {